Uncovering Hidden Details In the Shadows. There are usually significant details hidden under the weight of the darkest parts of an image. These darker details are very rich and revealing, and to some extent they are recoverable, but they must be carefully extrapolated. The reason why these details are hiding has to do with the default linear tone mapping that takes place in the camera when the image is being captured. While image sensors see light linearly, the human eye doesn’t!
Notice the illustration below. The reason the top gradation stripe looks “natural” is because that’s the way your eye registers light; pretty evenly distributed across the range. The bottom strip is how your camera parses that same volume of light.
Compared to human eyesight, digital camera sensors are biased in the way they capture light. It is a known fact that over half the luminance range captured by digital cameras favors the lightest tones in the picture while the darkest tones are quite slighted. When an image is opened in an image editing application, the highlight and quarter-tone detail is lavishly represented while the shadow/three-quarter tones are scantly recorded. Put simply, the image sensor is designed to dynamically record light. The brighter the light, the more information is recorded. Where I come from, this is called blatant discrimination!
It is for this reason that capture saved in RAW format can be a bit overexposed (when looking at the on-camera histogram). There is always more information present in the image than the histogram can reveal. Truth be known, the beloved histogram only displays the relative values of just 128 tones. Considering the fact that normal 24-bit color photos can display over 16,000,000 colored tones, there are more than enough tones to spread around without encountering objectionable “posterizing” effects.
Above, you see a published example of an image significantly lacking in shadow detail. To the left you see the histogram of that image. Notice that the shadow side of the histogram is not slammed up against the left side. This is a good sign. There is still room for adjustment.
Above you see that same image after the shadow tones have been moved into the middle tones, resulting in the whole image brightening and showing more detail. Notice the histogram to the left. In spite of this image being a second generation JPEG, there was ample detail in the shadow region that just needed to be opened.
Also notice that this shift of the shadow tones didn’t affect the quarter-tones and highlights. Remember, detail is a product of internal contrast. If you want to see shadow detail, you’ll have to “expose” the internal contrast within the shadow tones. The key to good photo interpretation is balance, and balance is governed by the type of lighting in the scene (high key, normal, low key, etc.) Learn to interpret the effective light range (either at exposure or during editing) and take bold steps to deliver both smooth transitions and visual detail.
What to do? Because of this “weighted” light range reality, three imperatives become evident for editing digital images. First, capture your images in your camera’s RAW format (perhaps in conjunction with a high-level JPEG format. Second, slightly overexpose your images. Remember, your camera is capturing vast levels of quarter tones and highlight detail. And third, get serious about spreading out the lower end of the contrast range in RAW Interpreter software like Camera Raw or Lightroom. The editing tools present in these nearly identical toolsets allows for significant internal contrast adjustments with absolutely no loss of detail.
Shadow detail is not nearly as fragile as some would purport. The lower range of the tonal range is quite visually robust. Don’t be afraid to push some of those three-quarter tones north toward the middle tones. Your images will thank you. One more note about shadow details; they actually need to be separated to display properly. Separate those tones and watch the details jump out.
If you really want to understand what makes color work, you need to understand how light behaves. And here’s where I can help you. I’ve created a very entertaining and easy-to-understand video series that will teach you these fundamentals and get you on track to capture and produce amazing color. http://gottaknowvideos.com