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In this installment of Woodworkers And Digital Photography we will focus on taking the picture, that is capturing the RAW file. Much of what we have discussed will come into play here. The emphasis is on getting the correct exposure and composition. In Part 6 we will learn to use Adobe Photoshop Lightroom to develop the RAW file and in Part 7 we will finish up by using Adobe Photoshop CS3 to create the portfolio print.

My Shop Does Not A Studio Make

My Shop - Note The Walls And Garage Door - The Lighting Is FluorescentIf your shop is anything like mine, it is not conducive to photography. Certainly a photographer would not model a studio after my shop. My walls are construction plywood. I have numerous windows on three sides and often (weather permitting) I have a garage door open to the shop. The ceilings are white. The lighting is fluorescent mixed with daylight streaming in the sides. Reflected light from the ceiling is mostly fluorescent. From the walls it is a combination of fluorescent and daylight, but because of the makeup of the walls it is mostly yellow to brown. I don’t use either flash or studio lights. The former would cast harsh shadows and the latter take to long to setup and take down.

Use Low ISOs To Capture A Noise Free Image

Notice Noise On Face & Chest Due To ISO 1600 SettingThe light level produced by the lighting described in the previous paragraph is low. To obtain correct exposure I must use a rather long exposure time, a large aperture (low f-stop) or a high ISO setting. We didn’t discuss ISO in detail, but suffice it to say that at higher ISO setting more noise enters the RAW file and becomes visible as randomly colored pixels. These noise pixels show up mostly in the darker areas of the picture since that is where the light level is lowest which produces the lowest signal/noise ratio. Hence, we will always use ISO 100 or 200, maybe on a rare occasion 400, but no higher. Note the noise in the face and chest area of the picture at right which was shot at ISO 1600.

Stick With f-stops Between f/8 And f/11 For Good Depth Of Field

That leaves us with a large aperture or a long shutter speed. We know that smaller apertures produce larger DOF which is what we want. So we might decide to use the smallest aperture possible. But there is another problem. Below about f/11 the aperture is so small that it tends to produce diffraction related anomalies. We will use between f/8 and f/11 which will yield the desired DOF and will not destroy the quality of the image. We start by selecting the aperture priority mode (Av on the mode dial) set it to the desired f/stop. Next we set the desired ISO. Now we are ready to mount the camera on a tripod. Though we haven’t discussed a tripod since I listed the necessary equipment in Part 1, it should be obvious by now that we will end up using a long shutter time making the tripod necessary to avoid camera shake that might be produced by hand holding.

Small Image & RGB HistogramIf you have a good zoom lens and the situation allows, use the lowest focal length. This will produce the largest DOF. Sometimes I have a problem with fixed work stations getting in the way and I end up having to use the telephoto (higher focal length) range to get my subject in the picture. This occurs mostly with large pieces.

Take A Test Picture And Adjust Exposure

Now is the time to adjust the tripod for height, focus the picture and set the camera to timed exposure. We can use either manual or auto focusing, both should work just fine. It may be useful to limit the auto focusing and exposure points to just one, whether the center point or one that is most appropriate for the composition. Next we depress the shutter button half way to get an exposure reading, set our feet, take a deep breath and completely depress the shutter button. We do not move until after the picture is recorded and the file is transferred to the storage device. Usually a red light is available on the camera to let us know when this has occurred.

The Histogram Is A Useful Tool To Assure Correct Exposure – But Only A Tool

Small Image, RGB & Brightness HistogramAt this point we have a test shot which we can view on the camera’s LCD. We don’t remove the camera from the tripod or alter the camera or tripod’s position to do this. We simply choose the preview button. At this point the picture is not the most important thing to preview, rather we want to look at the histogram. The Canon 40D has two styles of histogram preview; one displays a small image with three separate red, green and blue histograms (above left) while the other includes a gray scale brightness histogram (right).

Histograms are simple. Don’t let them intimidate you. The x axis represents the intensity level from darkest on the left to brightest on the right, or quantitatively 0 on the left and 255 on the right. This provides 256 buckets. To create the histogram each pixel in the picture is placed in the bucket that correctly represents its tone or brightness level. In a bright or high key picture there will be many pixels in buckets that crowd the right of the histogram. In a dark or low key picture there will be many pixels in buckets that crowd the left of the histogram. In an evenly lit scene with highlights and shadows there is likely to be a single hump curve with most pixels in buckets near the middle of the histogram. Still some histograms will have two or more humps. The amplitude of the histogram tells you how many pixels fall in each bucket, the y axis. There is no one correct histogram shape. But there are some things that one should look for in a histogram – most importantly is exposure and how much data was captured.

In the above histograms ignore the picture itself, it is just one I took as an example. Also, when taking this snapshot I used the automatic program mode (P on the Canon) so the camera chose the shutter speed and the f-stop and focusing was automatic. Ignore all of this. What I want you to do is click on each image to enlarge it and notice that the picture is underexposed. You can tell this because the histogram is too far to the left. Notice the histogram has five zones and only three and a half of the lowest zones are used. This shows up in both the RGB and brightness histograms. Not only is this picture underexposed but we are not capturing as much image information as the camera is capable of. In fact we are probably capturing less than half the information available. If this were a picture with lots of detail and a full range of tones we would sorely miss this information when we attempt to develop the RAW file. More on that later.

Adobe Photoshop Lightroom HistogramThe brightness histogram is a sort of amalgam of the red, green and blue histograms. The algorithm for producing the brightness histogram from the RGB histogram is not trivial and varies from camera manufacturer to manufacturer. But you can see the general relationship is consistent. At left is another histogram, this one is of the very same picture but produced by Adobe Photoshop Lightroom. This histogram also shows that the picture is underexposed though there are no vertical lines to give you an idea how much.

Calibrate Your Camera’s Histogram

If you have never done it, you should take several pictures with your camera, under various types and levels of light, and compare your camera’s histogram to the that of Photoshop Lightroom. If there is significant difference make a mental note of what it is and how much. Photoshop’s histogram is likely far more reliable than your camera’s, so in the future adjust your camera’s histogram mentally to correspond with Photoshop. For example, if my camera produced the histogram we see here, one and one half zones underexposed, but when viewed in Photoshop produced a histogram that showed correct exposure (all the way to the right without blowout), I would then mentally adjust all my camera’s histograms about one and one half zones to the right. Of course this is an extreme example to make the point and your camera is not likely to be that far off. Nor should you base a correction on the result of just one picture, but a number under various conditions. By the way, notice that Lightroom displays secondary color histograms, as well as red, green and blue histograms.

Adjust Exposure Until It Is Correct And You Are Capturing The Available Data

Two Stools With A Gray Card In The PictureWhat we have learned from this test shot is that we have to adjust the exposure, increase it in this case. I would try increasing it a full stop and take another test shot. Since we don’t want to change either ISO or f-stop we can use the camera’s exposure compensation setting to accomplish this. Alternatively the camera’s bracketing capability could be used. I usually do this until I get the histogram I like. I must be sure not to go too far, or I will blow out the brightest pixels, that is render them as pure white with no detail.

Next I take another test shot, this time with a gray card in the picture as shown right above. Click on the picture to see an unadjusted enlargement. Notice there is a little too much yellow and magenta. I can use the fact that the upper right hand corner of the card is 18% gray, the bottom two are pure black and pure white and the upper left is a neutral gray. When I process it in Lightroom I can correct this color imbalance which is called white balance correction. The nice thing about shooting RAW is that I can do this in the computer, I don’t have to worry about it at capture time in the camera. Besides, Lightroom is far better at this than the software in the camera.

Take The Picture

Two Stools Color Corrected For White BalanceFinally, if I were shooting for my portfolio, I would remove the gray card from the picture and take the actual shot. The picture at left is the same composition, but I left the gray card in so you can see the color after corrected in Lightroom for white balance. Nothing else has been done. Notice the grays, black and white in the card are now correct. Though it may not be obvious to you, since you don’t work in my shop, I can tell that the other colors are also correct. The advantages of a gray card are many, but this is especially true in mixed lighting conditions – it can save a lot of work and trial-and-error in the development process. I actually have done this enough that I have characterized my shop and have a white balance template in Lightroom called SRWW Shop. Now I can take a photo without a gray card test shot and simply apply SRWW Shop to it when I load my RAW files into Lightroom. We will discuss this white balance technique more in the next installment.

Once More On The Advantages Of Shooting RAW

Converted To JPEG In CameraOne last subject I want to discuss before ending this installment is the advantage of shooting RAW. We have discussed this before, I know, but now I want to show you an example. The picture at right is a jpeg just as it would look coming out of the camera. Most DSLRs have the ability to shoot both RAW and JPEG at the same time. This picture is the jpeg image. I adjusted for exposure and color corrected the RAW image in Lightroom in 16 bit per pixel mode and then converted it to a jpeg file. The jpeg image was adjusted for exposure and color corrected in Photoshop CS3 in jpeg 8 bit per pixel mode and saved.

A JPEG File Format Edited In CS3 And Saved As JPEGProcessed In A RAW File Format And Converted To JPEG FormatThe RAW processed image is at left and the jpeg processed image is at right. They are very similar, as close as I could get them.

RAW Processed JPEG HistogramJPEG Processed JPEG HistogramNow let’s compare the resulting histograms. The RAW processed jpeg histogram is at left. The JPEG processed jpeg histogram is at right. Both histograms were produced by Photoshop CS3. Note their general shape is the same, but the JPEG processed JPEG histogram has missing data or more accurately missing tones, which can manifest itself as banding, the abrupt steps in tones instead of smooth undetectable transitions. This is caused by the camera throwing away large amounts of information when it converted, in camera, from RAW to JPEG. The picture at left was taken from the camera as a RAW file, processed in a RAW format, and then after all exposure and color correction adjustments were made, converted to JPEG. Since this picture retained all its information through its processing the resulting JPEG has many more tones and isn’t likely to show banding. This is a graphic demonstration of why capturing and keeping as much information as possible until the very end is critical. That is one major benefit of RAW. The other major benefit of RAW is that you can always go back to the RAW file and re-develop your picture, perhaps differently to create a different interpretation.

So far we have captured a picture in RAW format that is correctly exposed. In the next installment we will develop the picture in Adobe Photoshop Lightroom. See you in Woodworkers And Digital Photography – Part 6.

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Kit Information From Clockworks.comIn Shaker Style Chain Driven Wall Clock I wrote about clockworks I purchased for a clock case I am designing and building. The clockworks came nicely packaged but with no information to help in the design of the clock case except for the picture at right. I called the company I purchased it from and they essentially said, sorry, there is none to be had. An exhaustive search on the Internet for a PDF file failed. Fortunately, with the help of AllExperts.com I was able to reach a clock expert. AllExperts.com put me in touch with Charles Barrett of Die Klockwerken Antique Clock Repair & Restoration. Charles was able to answer all my questions which are listed below:

  1. What is meant by 7 ½” swing?
    I assume it means if the case is more than 7 ½” wide (e.g. 8″ or more, it should not interfere with the bob.
  2. Do the weights fall below the pendulum for an 8 day period? If so, how room should I allow?
  3. How do you attach the gong so that the hammer (one hammer) can strike it appropriately? Can it hang from a board or will that kill the sound?
  4. How far back should the movement be from the plane of the dial?
  5. What cutouts are needed on the seatboard?

As I suspected, 7 1/2″ swing was the minimum distance of the internal wall required to make sure they did not interfere with the pendulum. Charles recommended at least 8″. Since my dial is 10 1/2″ wide which dictates the inside width of the case, there is plenty of room.

Another important question whose answer dictates the case dimensions is how far the weights must fall to provide full eight day clock operation. The skimpy information provided on the suppliers website says the pendulum will hang 34″ from the center of the dial. But does the weights fall below the pendulum and how much? Charles answered this way:

“The weights can fall below the pendulum and usually do for a 8-day run but it is hard to say just how long the critical length of the case drop should be to match the full 8-days. Reason being, is that it depends on the length of the weight shells. With that said, I would compensate a full length and a half weight shell length for max case length to achieve a full 8-day run.”

Coiled Gong, Mounting Rod & Back Of Movement Where You Can See The HammerThe weight shell length I measured to be 6″ which suggests the inside bottom of the case floor should be at least 34″ + 9″ or 43″ below the dial center. I decided to make the case height 51″ to accommodate this requirement.

I still haven’t figured out how I am going to mount the gong. As you can see from the picture it is a coil style gong. Charles answered question three as follows:

“Is the gong a coil gong or a rod type? In either event, be SURE that the gong is attached to the most dense part of the case (best if it is attached to the backboard of the clock case and be sure to use a REALLY solid hard wood for this since the mounting point of the gong is going to act as your sounding board.

The hammer strike point should be 1/4 to 1/6 of the length of the rod where the hammer strikes the portion of the rod CLOSEST to the mounted end of the rod–NOT the free end of the chime rod.

If it is a coiled gong, have the hammer strike the INSIDE portion of the flat portion of the coil closest to the mounting point.”

I think I will need to talk to him on the phone to unravel this one.

Question four I answered myself once I took careful measurements of all the important points. Also, I am using a 1/4″ backer board, called Dial Mount in my design drawings, which is different than just using the Clock Dial that came with the clockworks. But for reference here is what Charles said about the placement of the clockworks:

“The face should have come with the movement and is mounted to the movement by way of mounting pins on the back face of the dial that protrude through the front plate of the movement. When you close the door of the clock, be sure that you allow 1/4″ clearance measured from the end point of the hour pipe so that it doesn’t interfere with the glass door.”

The seat board is a critical item in the case design. Get it wrong and the clock will not work or will not align with the center of the clock dial. Either is catastrophic. Charles described the cutout requirements as follows:

“Seatboard will have cut-outs for a. chains/cables, b. short cutout for the leader travel on the rear of the seat board closest to the backboard of the case, c. mounting hold-downs for the movement in relation to the threaded posts that connect the front and rear plates together.”

The Seatboard Design Resulting From Careful Measurements

The Seatboard Design Resulting From Careful Measurements

Since I received no documentation I had to make measurements of the clockworks to precisely place these cutouts. This is tricky because the posts connecting the front and back plates together are not symmetrical relative to the center of the hour pipe (the pin that drives the hour hand), the hour pipe is not centered on the front plate, and the gears that support the chains are not symmetrical relative to the hour pipe. I used the center of the hour pipe and the front side of the front plate as reference points for the clockworks and the intersection of the center line and top front edge of the seatboard as reference points for it. After careful measurements, and allowances for tolerances, I came up with a seatboard design as shown.

Because these design choices are so critical to the operation of the clockworks I am going to build a mock-up that will allow me to actually see how well they serve the design. I’ll get back to you in Shaker Style Chain Driven Wall Clock – Part 3 on the results.

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In this installment we are going to focus on the RAW file format and explain why it is important to shoot in RAW versus JPEG. I shoot exclusively in RAW, no matter the type of photography I am shooting. You may discover that you may also want to shoot RAW after reading this blog. I also convert my camera’s native RAW format to DNG, a RAW file format developed and maintained by Adobe as a standard format. More on DNG in the Part 5 installment.

Capturing An Image On The Digital Negative – Sensor

Before getting into the tradeoffs of RAW vs JPEG we need to discuss a little about how a digital camera captures a picture. The sensor is the heart of the digital camera. It is a semiconductor chip designed as an array of light sensitive cells. As mentioned in Part 3, there are two types, CCD and CMOS. In today’s technology which type is used is not a significant factor in the resulting picture quality. We will not go into the details of differences here. In both technologies the sensor’s array has an aspect ration and size; some are full format size equal to a 35mm camera which is  actually 36 x 24mm, and some are smaller such as the Canon 40D which is 22.2 x 14.8mm. The former are typically found in professional DSLRs which sell for $2,000 or more. The latter are found in the high end amateur and prosumer DSLRs such as the Canon Rebel and the Canon 40D respectively. These Cameras range in price from $800 to $2,000. In the last installment we discussed in some detail the effects of a smaller format on lens behavior and image noise. For this installment, there is little difference between format sizes relative to shooting RAW versus JPEG.

The aspect ratio is something to consider. Most DSLRs that are not full format (35mm format) tend to favor an aspect ratio which is more inline with how we humans like to see things. A typical ratio is 1.5:1 and this translates to 3888 pixels by 2592 pixels in the Canon 40D which is a 10.1 mp camera.

Bayer Pattern and Blur Filters What the sensor size and aspect ratio mean is that the sensor, in the case of the Canon 40D, has 10.1 million light sensitive sites arranged in an array, 3888 sites by 2592 sites, on a semiconductor die that is 22.2mm by 14.8mm. These sites are NOT sensitive to color by themselves. They are sensitive only to light intensity; each site counts the number of photons striking it and converts this to a stored charge or voltage. To register color a mask of three filter colors – red, green and blue, the primary colors – is placed over the entire chip (die). This mask is arranged in such a way that only one red, or green or blue filter resides over a site. Further it is arranged in rows of alternating red and green followed by blue and green. This is called a Bayer pattern and it results in twice as many green filters as red or blue. This is because the human eye is much more sensitive to green than either red or blue. There are other filter methods of capturing color information on a sensor, but this is by far the most prevalent. See the figure above left for better understanding of the Bayer pattern.

In addition to the Bayer mask there is a blurring filter which blurs the image slightly, not so much that it can’t be corrected with software later, but enough to help capture color information. I will not discuss details of this but be aware that, because of the blur filter, all images have to be sharpened slightly to recapture their original sharpness.

One other feature of a DSLR we discussed earlier is the bit depth, that is the number of bits of resolving power in each pixel’s sense amplifier. This can be anywhere from 8 to 16 bits with most DSLRs having 10, 12, 14 or 16 bits, more commonly 12 or 14. The Canon 40D has 14, which means it can capture up to 16,384 levels of brightness in each pixel. After demosaicing this translates to up to 14 bits of (or 16,384) brightness levels per red, green  and blue channel. I say “up to” because whether it captures this much information depends on the scene and the exposure. More on this later.

Internal Processing When Shooting JPEG

One thing you may notice is that the Bayer pattern effectively cuts the number of pixels by a factor of three, that is, no pixel has all three colors, it only has information about red, green or blue. So does that mean the Canon 40D is a 3.3 mp camera? No. What the internal processor does is perform calculations on each pixel site, using information from its nearest neighbors, to reconstruct the pixel with full color information for that site. This interpolation step, called demosaicing, is a proprietary algorithm and may differ from manufacturer to manufacturer and even from model to model within a manufacturer’s line. Further, demosaicing is a complex algorithm which requires a lot of compute power and time, neither of which your camera has. The camera has to be ready for the next shot, hence the manufacturer has to make a tradeoff between burst rate and quality of processing algorithms.

I am not going to go through all the processing steps the camera performs when shooting JPEG. Suffice it to say there are many such as colorimetric interpretation, color space calculations, white balance, gamma adjustment, contrast adjustment, color adjustment, noise reduction and sharpening to name a few. Many of these are a function of settings the photographer directly chooses and some are secondary choices the camera makes.

After the aforementioned processing steps the internal processor performs an 8-bit conversion, JPEG compression and file storage. The level of JPEG compression is chosen by the photographer.

Finally, after all the above good work, the internal processor does the most sinful thing, it throws away every piece of RAW information (unless you choose shooting RAW + JPEG). You now have a JPEG file with 256 levels of brightness per color channel versus 16,384 and you have lost all information regarding original exposure, contrast, white balance, color saturation, sharpness, etc.

The RAW File – An Exposed Film And More

Imagine (if you are old enough) a 35mm film with the following qualities:

  • The film can be exposed at any ISO you choose within the camera’s ISO range.
  • Once exposed it need not be stored in a refrigerator to prevent its exposed contents from degrading. In fact, it can last for 100 – 200 years without degradation on a gold backed CD or DVD. It can last forever if the CD or DVD is reproduced regularly (say once every 100 years).
  • It can be developed over and over without changing the films content, that is, it always remains an exposed and undeveloped film even though it is processed (developed) any number of times.
  • You can process it a few ISO settings higher or lower than the ISO it was exposed at without loosing visible detail.
  • When processing (developing) you have complete control of all the steps applied to the equivalent JPEG capture from demosaicing on, and you can still produce JPEG images in the end.
  • The information available to correct any mistakes in shooting is far greater than in JPEG images.
  • Its dynamic range is greater than JPEG and can be manipulated to produce a High Dynamic Range print.
  • Each and every picture on the roll can be developed (over and over) with a different process, meaning different exposure, white balance, contrast etc.
  • All information concerning exposure (f/stop, shutter speed and ISO), camera make and model, date and time of exposure, copyright information and much more is contained in the file (this information is also available in the JPEG file).

 

Sounds good? Well that is exactly what RAW files are. Nearly a panacea for the photographer.

The Pros Of Shooting RAW vs JPEG

  1. All Processing, from demosaicing on, is done by RAW converter software on your desktop computer. Most RAW converter software packages, such as Lightroom and its Camera RAW engine, can take more time and use better algorithms than the camera can. Remember, as mentioned earlier, the camera has to be ready for the next shot, hence the manufacturer has to make tradeoffs between burst rate and quality of processing algorithms.
  2. RAW files are compressed using lossless compression techniques. This means all image information is forever available to the photographer or developer. JPEGs are stored as lossy compressed files. This means image information is discarded in favor of smaller storage file size and can never be recaptured.
  3. More control over many of the processing and exposure parameters. For example you can choose any white balance combination of temperature and tint. This is useful especially in mixed light environments. With JPEG shooting you typically have to choose between “Daylight”, “Overcast”, “Cloudy”, “Fluorescent” or some other discrete choice. For the woodworker who is shooting in a workshop with mixed fluorescent and daylight, this can be very important.
  4. With RAW a color space can be chosen anytime or changed at anytime. With JPEG a color space gamut has already been applied which may be inappropriate for the end use.
  5. RAW maintains its 12 bit or 14 bit information, whereas JPEG files are gamma compressed 8-bit data. JPEG suffers from information loss due to compression and its resultant artifacts, and in addition its 8-bit conversion can produce unwanted quantization artifacts.
  6. Because RAW files have more image data to begin with, large changes can be made without introducing artifacts, such as large changes in exposure. Such changes will almost always produce artifacts in JPEG images.
  7. The photographer can concentrate on image composition, focusing and exposure. All other decisions can be handled in processing (white balance, contrast, color balance, sharpness etc.). With JPEG you must make these decisions prior to capture.

The Cons Of Shooting RAW vs JPEG

  1. The largest drawback to shooting RAW is the large file size, typically 2–4 times that of JPEG. This means fewer pictures on a memory card between card changes. This can be a problem for sports or wedding photographers, but it is not a problem for the woodworker trying to capture images of his or her work.
  2. Since RAW images are much larger, fewer can fit in the cameras buffer before being written to the memory card and writing them to a card can take longer. This results in fewer pictures taken in a burst. Again, a problem for the sports photographer but not the woodworker.
  3. JPEG is a standard. RAW is not actually a file format, it varies from manufacturer to manufacturer, and even from model to model, and the file extension is usually not .raw but different for each manufacturer, and RAW is certainly not a standard. However, I will discuss in Part 5 how this is ameliorated by downloading the camera’s card and converting its RAW file at the same time to Adobe’s DNG RAW file format.
  4. Because RAW files are proprietary, it can take some time from camera introduction until a RAW file converter supplier can reverse engineer the file structure and support it. Adobe seems to do this in a matter of a few weeks, so this is not a big problem.
  5. RAW image workflow, the sequence of steps needed to process (develop) RAW images, can be significantly longer than JPEG. The tradeoff here is quality of image verses your time. If you spent significant time crafting a piece, I would suspect you want its entire beauty visible in your portfolio picture, and the relative time of developing to crafting is small.

I would like to discuss the RAW image bit depth in more detail so that we can have a better basis for determining correct exposure which we will discuss in the next installment. As mentioned earlier, RAW images capture large numbers of brightness or tone levels, in the case of the Canon 40D 14 bits worth. A little binary arithmetic is in order; 14 bits can represent any decimal number from 0 to 16,383 or 16,384 levels. Like decimal arithmetic, the most significant digits hold the most information. For example, if a decimal number has three digits left of the decimal point it can represent 1000 steps, 0 through 999. If there are only two digits it can represent 100 steps, 0 through 99. Finally if it has one digit 10 steps, 0 through 9. Note that as we lost a most significant digit we went from 1000 possible steps to 100 to 10. Clearly the highest order digit holds the most information.

In binary arithmetic you have the same situation except the only numbers are zero and one. If the most significant 14th bit is set to a one and the rest can change, you can have 8,192 steps (8,192 through 16,384). If the 14th bit is set to zero you can also have 8,192 steps (0 through 8,191). Now suppose the 14th bit is always zero and the 13th bit can change between zero and one? How many steps can you have? The answer is 4,096 in each case ranging from 0 through 4,095 with the 13th bit set to zero and 4,096 to 8,191 with the 13th bit set to one. If we were to leave the highest two bits pinned to zero we would have two groups of 2,048 steps and so on down to two steps when only the least significant bit can change and all the higher bits are pinned to zero. Now imagine that when any bit position is a one it is a bucket. The maximum number of steps that bucket can hold is a function of its position or order. The total number of steps is 16,384 for a 14 bit binary number. This is shown in the table below. Note that the sum of all numbers in the bottom row is 16,384.

 Bit Position vs Tonal Steps

So what is the significance of this and why are we spending so much time on it? Note that bit 14 can hold half the total tonal (brightness) information, while bit 13 can only hold one quarter the total tonal information, bit 12 one eight and so on. If you want to capture the most possible information in an image, you have to choose an exposure that will set all bits for some number of pixels, but leave no pixel asking for more tonal steps. If the exposure leaves some pixels asking for more tonal steps than 16,384, the camera can not accommodate it and the information is lost. This is called blowout in photographic parlance. Similarly, but more importantly, if no pixel sets bit 14 to a one, the most tonal steps the captured image can have is 8,192, the other 8,192 lost because bit 14 wasn’t used in the chosen exposure. If neither bit 13 nor 14 is set by any pixel, the maximum tonal range is 4096 steps, only one quarter of the camera’s capability. This is called underexposure in photographic parlance.

Note another point. JPEG files only have 8 bits of depth. From the above table you can see that means 256 steps of tonal information (the sum of the bottom numbers starting from 1 to 128). If a scene is captured in a RAW file with optimal exposure you must squeeze 16,384 tonal levels into 256 tonal levels in the conversion to JPEG. Imagine the loss of information. In the other extreme, if a scene is captured in a RAW file with a sub-optimal exposure that uses only the first 8 bits, then converting this to a JPEG is not a lot of information loss because 8 bits fit nicely into 8 bits. But hey, you didn’t capture much information to begin with.

If you recall, that is, if you did much 35mm film photography, you were taught to expose for the shadows and adjust for the highlights later. In digital photography it is just the opposite. You expose so that you use all of the bits available to you, but no more. This means exposing to correctly capture the highlights without overexposing (although when you shoot RAW you can overexpose a little and good RAW converters can use magic to recover a little). This exposure technique will be covered in the next installment when we discuss image capture which includes the introduction of tonal histograms.

Summary

Shooting RAW has many advantages and is the only way to maximize the image quality your DSLR is capable of. It comes at a some cost, but most of that cost is insignificant to the woodworker trying to capture the beauty of his or her work. It is not enough to shoot RAW to maximize the quality of your image, you must also expose your image so that it uses all the tonal range your camera is capable of; this means exposing for the highlights without blowing them out. Underexposure wastes large amounts of information which cannot be retrieved.

When you purchase an expensive DSLR, ask yourself, are you buying it for its ability to capture high quality images, or its superior conversion algorithms? If the answer is the former, most of that image quality may be thrown away when shooting JPEG. If the answer is the latter, sorry, you are fooling yourself. RAW converters, the really good ones at least, do a better job of developing RAW files than the camera, and cost a lot less.

See you in Woodworkers And Digital Photography – Part 5 where we will put Parts 1 – 4 together into a discussion of capturing images. Part 6 will begin a discussion of developing images using Adobe Photoshop Lightroom. Bye for now.


Mechanical Movement, Bob, Weight and ChainMy youngest daughter recently graduated from law school and passed the bar. Her swearing-in ceremony occurred on Friday December 12, 2008, the day of the Ice Storm 0f 2008. I was without power, and trees and power lines were down in my driveway, preventing me from attending. But the law marched on without me and she is now an attorney with a Boston law firm.

Kit Information From Clockworks.comMy gift to her for the effort and years she labored to achieve this event will be a Shaker style chain driven wall clock. The mechanical 8-day clockworks will be driven by weights and pendulum. The pendulum is 34” long from the dial center to the bottom of the swing. Hence, the clock case will be rater long, about 48”

The clock case design will be similar to the Tall Shaker Wall Clock shown on my Gallery page. However, the lower door panel will be glass so you can view the weights and pendulum – and of course the shelves will be removed. The clockworks are Hermle 241-080 ordered as a kit (see Hermle – Chain Driven – Gong Strike – Item #KIT10) from Clockworks. I was surprised to discover that Clockworks is located in Huntington, MA, not more than a few miles from Swamp Road Wood Works, home of Chiefwoodworker.

Wide SwingMost clockworks suppliers will tell you not to design or build a case until you have all hardware in hand (clock movement and other pieces). There is a good reason for this sage advise. The only installation instructions you receive is something akin to the picture shown at right above. You may have to click on the picture to enlarge it to see the information provided. The first question I asked myself is what is meant by 7 1/2” swing? There are are lot of other questions, like how big is the bob? How far back should the movement be from the plane of the dial? What cutouts are needed on the seatboard? How do you mount the movement to the seatboard? The chains in this picture appear to be in front of the pendulum; one hopes that is not true. The questions are many, and the only way to find out appears to be reverse engineering.

Narrow Swing Fortunately, I draw my plans in 3D using SketchUp. So I made a couple of quick drawings to get answers to the first question – what is meant by 7 1/2” swing? I figured there are two possible extremes, a wide swing shown in the SketchUp drawing at left, and a narrow swing shown at the drawing at right.

The wide swing has the bob extending beyond the clock dial edges, which means the inside width of the case would have to be wider than the clock dial. This seems unlikely to me. On the other hand, the narrow swing seems tool little a swing to drive the clock, but maybe not. Anyway, I sent these drawing to Clockworks and asked for clarification. Hopefully they can help.

If not, I will set the clock up in a makeshift case and take a number of measurements before beginning detailed drawings.

I will add updates to this post as I progress, so stay tuned.


I would like to repeat that this tutorial is directed at woodworkers, not photographers. What I will cover relates to how a woodworker can use photography to enhance his/her woodworking. Generally this means photographing stills for a portfolio, website, blog, or even capturing wood grain to use for texturing a SketchUp model. What we will not discuss, and what is not implied in anything I cover, is nature photography, portraiture, sports photography, macro photography etc. The camera, lenses, other accessories, techniques, software et al are often different between photographic styles. Today we are going to focus on the camera, or more specifically the camera body; its features and specifications that make it more suitable for woodworking photography.

Digital Single Lens Reflex – DSLR

The preferred camera, and the only one we will discuss here, is the Digital Single Lens Reflex or DSLR camera. These cameras are very similar to their 35mm cousins, although both SLR and DSLR have replaced largely mechanical  innards with almost entirely electronic innards these days. What is important about an SLR is that you see in the viewfinder exactly what the lens sees. In fact, the viewfinder is getting its image by redirecting a portion of the light that passes through the lens to the viewfinder with the aid of a mirror.

Not only does the viewfinder see what the lens sees but it can also see the depth-of-field (DOF) produced by the lens and its f/stop setting. This is accomplished by depressing a DOF preview button, available on most DSLR cameras. This button stops down the aperture diaphragm which allows you choose an f/stop that will produce the desired DOF which can be evaluated in the viewfinder.

Many DSLR cameras have an exposure mode selection that is essentially a DOF priority mode, much like aperture priority or shutter priority. On my Canon cameras it is called A-DEP for automatic depth-of-field. What A-DEP does is automatically choose an f/stop that will maximize the DOF for most of what is in the scene. It then chooses an ISO and shutter speed that will give correct exposure.

In both of these cases, either manual setting of f/stop or A-DEP, you are likely to end up with a small aperture and long shutter speed, because you will want the maximum DOF to ensure your woodworking piece is in total focus. Long shutter speed means camera blur unless a tripod is used, and that is why a tripod was listed as necessary equipment in Part 1. Almost all the photographing we will do as a “woodworker photographer” will be with a tripod.

While we are still on SLR features, many of the new DSLRs have a feature that allows you to see the image on the LCD instead of the viewfinder. On the Canon this is called Live View. Normally, when shooting hand held, I would never use this feature. But it does come in handy when the camera is mounted on a tripod, especially when the height of the viewfinder ends up higher or lower than eye level. It also allows both manual and auto focus. In addition, for manual focus, you can zoom the LCD 5X or 10X for easier and more accurate focusing. This is a really nice feature when shooting on a tripod.

ISO – As In Film Speed

ISO is an acronym for International Standards Organization (more precisely International Organization of Standards). In photography it refers to the standards adhered to by film manufacturers or digital camera manufacturers. Remember when you went to the drug store and bought ASA 100 film for outdoor shooting, or ASA 400 for indoor shooting? Well, ASA and ISO are equivalent arithmetic scales that define the amount of light a film required for correct exposure. ASA or ISO 100 film required twice as much light for correct exposure as did ASA or ISO 200, and four times as much as ASA or ISO 400. When digital cameras came along the manufacturers adhered to the same ISO standards for adjusting the “sense amp” levels on sensors. Don’t let the technical term “sense amp” throw you, it simply means sensitivity.

Three factors decide correct exposure: ISO setting, f/stop setting and shutter speed. Like f/stop and shutter speed, discussed in Part 2, ISO settings come in standard values as shown below:

100, 200, 400, 800, 1600, 3200, 6400, 12800

Some cameras may eventually go much higher than ISO 12800, but for now it is pretty much a useless setting save for emergencies. There are two things that should be obvious from this progression of numbers. First, each one is twice the previous in numerical value. Second, this doubling/halving relationship is very much like shutter speed and f/stop full steps. This is not a coincidence. As you go up in ISO, each step in value requires half the light for correct exposure as the previous value, and just the opposite as you go down. So for any lighting condition there is a very large combination of ISO, f/stop and shutter speed that will satisfy exposure. The photographer chooses different combinations depending on the artistic effect he or she is trying to produce in a print.

As woodworkers we will opt for ISO 100, 200 or 400 combined with a small aperture and long shutter speed. The low ISO ensures little noise or grain in the picture, the small aperture produces large DOF and the long shutter speed is the price we pay, the latter mitigated with the use of a tripod.

Exposure Modes

Like 35mm SLRs, DSLRs come with a rich set of exposure modes. My Canon 40D has the following:

  1. Portrait, Landscape, Close-up, Sports, Night Portrait, Flash Off
  2. P, Tv, Av, M & A-DEP
  3. Three Custom Modes C1, C2 & C3

Group 1. is called Image Zone or Non-Creative Zone meaning they are pretty much fully automatic. The photographer trusts the camera to produce a reasonable result. Group 3. can also be fully automatic but the photographer has a say in many of the settings, but not at the time of image capture. Group 2. is the creative modes or zones. P stands for Program Auto Exposure, Tv for shutter priority, Av for aperture priority, M for manual and A-DEP for automatic DOF.

We are interested in Av, M and A-DEP. Av allows you to choose an aperture setting and ISO manually. It then determines the correct shutter speed. Aperture priority means you give priority to the aperture and let the automatic exposure system choose a corresponding shutter speed. Of course, if you want to choose all three manually (aperture, shutter and ISO) you can use M. As mentioned before A-DEP, a sort of DOF priority mode, chooses both f/stop and shutter automatically, but gives priority to DOF. The internal microprocessor evaluates the scene and adjusts f/stop until nearly the entire scène is in focus. Then it chooses an appropriate shutter speed. Focusing  in any of these three modes can be either automatic or manual and can be achieved through the viewfinder or LCD providing your camera supports it.

File Format or JPEG vs. RAW

No matter what kind of photography I am doing, woodworking or any other, I always shoot RAW. Professional photographers will argue that this is wasteful in terms of file storage, development time, and even capture time if you are shooting sports scenes. But I am not a professional photographer, I am an adult, and I can shoot the way I want. Besides, I think I have good reasons to do so. First, let’s discuss what JPEG and RAW are. Every time you snap a picture with a DSLR an internal microprocessor captures information from the light sensitive sensor (electronic film), manipulates that information according to a number of algorithms and finally stores it on a memory chip according to some file structure. Common file structures are TIFF, JPEG, RAW, and many others I won’t mention here. RAW is actually a general classification of file types specified by each camera manufacturer. For example Canon uses .CRW and .CR2, Nikon’s RAW file is .NEF and Panasonic actually uses .RAW. There is only one quasi RAW standard and that is Adobe’s .DNG for digital negative. Adobe can take almost any RAW format and convert it to a .DNG RAW format with no loss of data. Adobe hopes one day it will be accepted as a standard and will be supported by all cameras so that a conversion isn’t necessary. It hasn’t happened yet.

You can mentally classify each file type by whether it is a compressed file or not, and whether the compression algorithm used is lossy or lossless. Most file formats are compressed to some degree. This helps to reduce storage space and improve transport time. Some compression algorithms compress files a lot, even to the point they sacrifice image content and quality, provided the end result is not too discerning by the eye.

TIFF (Tagged Image File Format) is a compressed file using lossless algorithms. It is used widely in desktop publishing, page layout and faxing applications. Of the three formats it is usually the largest. Many DSLR support or once supported TIFF, but are now focusing (no pun intended) on JPEG and native RAW.

RAW is a lot like TIFF in that it is compressed but using lossless algorithms, that is, the entire image content is preserved. RAW is generally compressed more than TIFF and hence smaller. But while TIFF is a standard, as mentioned RAW is different for each camera manufacturer. Why is that? Well it is probably equal parts of proprietary advantage, and different sensor technologies. Too complex for this tutorial, maybe another time.

JPEG (Joint Photographic Experts Group), like its motion picture equivalent MPEG (you guessed it – Motion Picture Experts Group), is a highly compressed file using lossy techniques. Many DSLRs allow you to choose levels of compression, sacrificing picture quality even more for smaller file size, hence more pictures on a memory card.

In most DSLR cameras RAW files are 3 to 4 times larger than their JPEG equivalent (equivalent in resolution, not quality). This is why JPEG is so popular. But there are a number of drawbacks to JPEG. First, JPEGs are highly processed by the camera. That is, depending on the Image Zone, custom setting, white balance and exposure you choose, the internal microprocessor “develops” the picture for you and then produces a JPEG file. Once the picture is developed, the original information is thrown away by your camera. It is akin to developing 35mm film. Once you put it through the chemical baths and develop it, you can’t go back. If you developed it poorly, sorry, deal with it!

RAW on the other hand is like exposed, but undeveloped 35mm film, but better; it lasts forever. You can develop it with a computer application such as Adobe Lightroom, but the development is non-destructive; the original file is left intact so that you can develop it again with a different “formula”. Try that with 35mm film.

Now some will argue that you can take a JPEG file and redevelop it in Lightroom or some other application. Not so fast! That is akin to taking a processed 35mm film (already developed), copying it via camera or scanner, and then developing that picture into a JPEG. The result is two layers of lost data. The point is, once you loose the information a camera throws away after creating a JPEG, you can’t get it back.

How much information are we talking about? Well there are three types of loses. The first is due to the compression which is lossy. The second is due to the choice of file format. The third is due to the fact that we developed the image, which means we made choices, perhaps bad ones, about exposure, color, contrast etc.

The file format is a big information loss, as is the developing. JPEG images are made up of pixels, the number of which depends on the resolution, e.g 10 megapixels. Each pixel has a Red, Green and Blue channel, and each channel is 8 bits deep. A little binary arithmetic says that is 256 tone levels per channel. RAW images on the other hand, are also made up of pixels with a Red, Green and Blue channel. But RAW images, depending on the camera manufacturer and the model, have from 10 to 14 bits per channel going to 16. My Canon 40D has 14. Again, binary arithmetic tells us that is 16,385 tones per channel compared to 256. Now before you say “Oh my God! I can’t believe the difference.”, even I have to admit not all that difference is perceived. The eye is a logarithmic beast. For example, shining twice as much light on a subject is not perceived by the eye as twice as bright. None the less this is a huge difference especially when it comes to artifacts introduced when we adjust color, white balance, contrast etc.

How this plays out will become more clear when we discuss Adobe Lightroom and image development. In fact, I may break the Adobe Lightroom installment into two installments to cover RAW vs. JPEG in more detail. I really feel strongly about RAW.

The Sensor – Digital Film

Perhaps the most important part of a digital camera is its sensor, that small rectangular semiconductor chip that lies on the focal plane of the camera. That is where the lens focuses the image, it is where the light intensity and color are registered and it is where the ISO speed is determined. More important than all of that, it is where the quality of the image is determined. You may read a lot about CCD (charged couple devices) vs. CMOS (complimentary metal oxide semiconductor) sensors. Go ahead and read it for education purposes, but in today’s technology world, both produce extremely good sensors. If I had to guess, CMOS will probably dominate or even eliminate CCD in the end, if for no other reason than the research infrastructure and manufacturing equipment infrastructure heavily favors CMOS. But as I said, if you buy a DSLR from one of the big guys (Canon, Nikon, Sony, Panasonic etc.) trust them to make the choice in technology. They are good at it.

What you want to look for are reviews by people like Digital Photography Review (www.dpreview.com) focusing on image quality. These people do a good job of quantifying the objective aspects of image quality. That said, here are a few things you can evaluate when comparing sensors:

  • Resolution – As stated earlier, 10 megapixel is probably more than you will need. If you go higher make sure the sensor is physically large enough to produce high quality images (more in a moment).
  • Bit Depth – Ideally you want 16 bits per channel, but 10 is ok, 12 better and 14 is great. Bit Depth determines the resolution of the sense amplifiers that detect the light falling on the sensor.
  • Sensor Dimensions – I am not talking about aspect ratio here. I mean the actual physical dimensions of the sensor. Other things being equal, bigger sensors, or more specifically, the larger the area per pixel of resolution, the better.

 

The second point above gets to the issue we discussed in the previous section on RAW vs. JPEG. We want a lot of tonal information in our RAW file. This will give us a lot of room to correct all kinds of problems in the final rendering without creating unwanted artifacts common when capturing only JPEG files. I will demonstrate this visually when we discuss RAW files and Adobe Lightroom further.

The first and third points above are similar in some respects. You know that you can purchase a 10 megapixel point-and-shoot camera for around $100. You will also spend about $1,000 for a 10 megapixel Canon 40D. What’s the difference? Well a lot of things including lens quality, body design, shutter speeds and quality, functionality etc. But one of the large differences is the physical dimensions of the sensor. Semiconductor real estate is very expensive. In point-and-shoot cameras the manufacturer can’t afford to use much of it. So the sensors are tiny. However, specs sell, so manufacturers have to offer a 10 megapixel specification, even for a $100 camera. The problem is that the area per pixel is very small, which means there isn’t much silicon (semiconductor) to sense light, hence low signal. However, that same small silicon can be heated more readily by surrounding circuits, hence more noise. This makes the Signal/Noise ratio low, not what you want for high quality images.

Higher end DSLRs use larger area chips to sense the same 10 megapixels. Hence large Signal/Noise ratios, producing higher quality images and higher ISOs. But even in high end DSLRs it is important that you compare square mm/megapixel. Here is an example:

  • Canon Rebel XTi, 10 mp, 22.2 x 14.8mm sensor, 12 bit depth, 32.9 sq mm/mp, very good image quality
  • Canon 40D, 10 mp, 22.2 x 14.8mm sensor, 14 bit depth, 32.9 sq mm/mp, great image quality
  • Canon 50D, 15mp, 22.3 x 14.9mm sensor, 14 bit depth, 22.2 sq mm/mp, great image quality but not as good as the 40D, especially in the higher ISO ranges (see www.dpreview.com)

 

While there are a lot of other differences between these three cameras, there are two that distinguish them one from another. The move from the Rebel to the 40D had more to do with bit depth. While the sensors were the same size, they weren’t the same sensors. I suspect the processing technology was improved in addition to improvements in the sense amplifier technology. The image quality improved as one would expect.

The move from the 40D to the 50D was kind of like the point-and-shoot tradeoff we discussed. In order to keep manufacturing costs consistent with the price range the silicon cost needed to be the same, hence the die size remained essentially the same. But to compete on specification the resolution was increased a whooping 50%. The image quality was actually slightly less than the 40D (more noise), though only in the higher ISOs. One has to wonder if this was a good tradeoff. Do we really need 15 megapixels in essentially a serious amateur/entry level professional camera? Isn’t image quality improvements with each generation more important? Don’t get me wrong, the 50D is an excellent camera, Digital Photography Review gave it their highest rating. But perhaps it could have been even better.

Exposure Metering

The last subject in this long camera installment I want to discuss is exposure metering. Most digital cameras have several metering modes, typically Evaluative, Center Weighted and Spot. These modes may have different names in different brands and models, but generally there is one mode that averages the entire scene and makes an exposure decision, a mode that looks at perhaps 30% of the scene around the center and makes an exposure decision and a mode that measures between 2 – 3% at the center and makes an exposure decision.

Spot metering is great. It allows you to choose a specific spot in the scene, perhaps a highlight, and expose for it. You can sample some number of spots and decide for yourself a correct exposure. The point is that it gives you options. The other two modes are more difficult to work with in terms of sampling a specific point or area. That said, the metering system in most DSLRs is quite good these days, so if your camera doesn’t support spot metering it is not a crisis.

In summary, the important features of a digital camera, as far as we woodworkers are concerned, are SLR technology, the ability to set ISO, support for Av aperture priority, DOF priority is a plus, LCD focusing, support for RAW files, a quality sensor and spot metering. It is now time to break. I will see you again in Woodworkers And Digital Photography – Part 4 where we will discuss RAW in more depth, especially as it relates to developing images in Adobe Lightroom.


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