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Index NX Gamma Tests

Mouse over to see how Capture NX resizes
Roll mouse over to see Capture NX resize gamma problem
Gamma encoded color spaces: Capture NX (2.3.2) takes a NEF, and converts it to a gamma encoded color space (like sRGB or AdobeRGB), and presents that to you within NX for editing. But, the only problem with this is that some (all?) adjustments within Capture NX are not gamma aware.

Why you should care: Not being 'gamma aware' means color shifts -- and since you are editing a NEF in the first place (instead of a JPEG), I am going to assume that you care about color accuracy.

An Example: Have you ever resized a photo for the web and noticed that you needed to brighten it slightly after resizing? If so, that was caused by your program not being gamma aware. Consider the calliphora photo to the right (original photo). Looks nice? It was resized in a gamma aware manner. But, roll your mouse over the photo to see how Capture NX resizes the photo.

Most people will never notice that NX Adjustments are not gamma aware. Most photos are well exposed and rarely heavily modified. But if your photo contains abrupt changes in contrast or color, or needs heavy editing, you will notice subtle shifts in color. I have noticed color shifts in several spots. (1) With D-Lighting, (2) in the recovery of extremely underexposed areas of photos, and (3) resizing photos smaller for the web.

Gamma Test Image
Classic Gamma Test Image: A classic gamma test is to create the image that you see to the right (green square over purple background) in your favorite image editing program and manipulate it (in NX, use this example.nef, produced with two colorize steps). The colors in this test image are very carefully chosen. The purple is RGB (255,0,255) and the green is RGB (0,255,0). These colors stay the same before/after gamma encoding/decoding. So we can then examine the averaged area between the purple and green to see if an photo editor is gamma aware.
It does not matter what color model you use! However, the internal RGB values in the color model must be set to the values as specified above. It is an ERROR to produce these RGB values in one color model and then convert the colors to a second color model (which will change the internal RGB values).

GOOD gamma aware result

BAD non-gamma aware result
Background: What happens when you rotate this test image? Some purple and green will have be 'averaged' together. Take the very simple case of one purple pixel (255,0,255) and one green pixel (0,255,0) that need to be averaged together. The result in a non-gamma aware program will be (128,128,128), which is half of 0+255 for red, green, and blue. But a gamma aware program would need to convert to linear (which is why the colors were chosen carefully -- the result is the same color), then averaged, which is (128,128,128), and then gamma encode that, resulting in (186,186,186). The results are obvious to see. (128,128,128) is dark color, whereas (186,186,186) is much lighter.

The Test: Rotate the test image by 5° and compare the results to what is expected from a gamma aware vs non-gamma aware program. A gamma aware program will have a pleasing white'ish blending. A non-gamma aware program will have an incorrect dark blending color.

Capture NX Test Results: Here are the test results for various Adjustments within Capture NX.

Distortion Control
Gaussian Blur

Given the dark blending seen, we can conclude the adjustments are not gamma aware. Given that these adjustments fail, I need to question if there are any adjustments within NX that are gamma aware.

Mouse over to see how Capture NX resizes
Mouse over to see how Capture NX resizes
More examples: There is an entire class of visual arts, called 'op art' (optical art) that is also noticeably affected, due to ultra-high contrast photos. Consider the op art photo seen far right. Roll the mouse over to see how Capture NX resizes and notice the color shift towards black. Also, a simple photo of zebras is also affected, due to the high contrast.
Why the shift towards black? Because a gamma unaware program will average black (0,0,0) and white (255,255,255) and produce an incorrect (128,128,128), which after gamma decoding by your physical CRT/LCD, equates to a linear color of (55,55,55), or gray at 22% intensity. However, a gamma aware program will average the two colors and produce (187,187,187), which after gamma decoding by your physical CRT/LCD, equates to a linear color of (128,128,128), which is gray at the proper 50% intensity.
Capture NX needs to be fixed: Presenting gamma encoded RGB to edit with non-gamma aware Adjustments is a design flaw, which only leads to shifts in color when the RGB values are edited -- as can be clearly seen in the above NX tests. Since many (all?) adjustments within NX are non-gamma aware in the first place, moving when gamma encoding takes place is the best way to fix NX. Currently gamma encoding in NX appears to be a hidden first step (when a NEF is converted to a color space -- and both the sRGB and AdobeRGB color spaces are gamma encoded color spaces).
How Nikon could easily fix Capture NX: Nikon needs to change when gamma encoding takes place within NX. And the solution to fix all of NX at once is deceptively simple. Gamma encoding in NX is currently a (hidden) automatic first step (with your screen/monitor being the gamma decoder). Instead, gamma encoding must instead be an automatic last step -- so that all adjustments work on linear color values.

See the fix for yourself! In NX: (a) add a first step with a gamma of .45 (Levels&Curves midpoint slider) to undo gamma correction and create a linear color space; (b) perform adjustments on these linear colors (like an image resize); (c) add a final step with a gamma encoding of 2.2.

Nikon Acknowledges the problem: I first reported the problem with Capture NX1 to Nikon in March of 2008, and again in February 2009 after I installed NX2. Nikon acknowledged that the gamma issue had been passed onto "Nikon QC".
Another very clever Gamma Test: Thanks to Eric Brasseur, who created a very extensive web page on the subject, for the following test image. Save the following specially created 258x222 Dalai Lama photo to your computer (right click on the picture, select 'Save Picture As...') and open in your favorite image editing program, then resize to 50% (129x111). What do you see as a result? A non-gamma aware program like Capture NX will produce a gray square. Something that you can see is incorrect. A gamma-aware program will produce the result that we can see is correct:

Original 258x222 test image
  Resize 50%  
NON-gamma aware resize

Gamma AWARE resize

sRGB vs. AdobeRGB
Color Profile Warning: I have seen posts on the Internet slamming the above discussion, claiming that if only the above photos were converted into the Adobe RGB Color Space that the 'problem' goes away. Of course the problem goes away!! Because by converting from sRGB to AdobeRGB, the very carefully selected internal RGB values are altered! These posts only confirm that color spaces are horribly misunderstood.
RGB(0,255,0) in sRGB, when converted to AdobeRGB, is changed to RGB(144,255,60). And RGB(255,0,255) in sRGB is converted to RGB(219,0,250)!
The above tests are about setting very particular RGB values within any color profile and seeing how NX2 handles the result. As such, use any color profile that you want -- but the color profile must be applied so that particular RGB values in the test above are performed.

Adobe RGB version: Here is a NEF with two versions in it (both in the Adobe RGB color space): (a) a non-gamma aware resize; and (b) extra gamma decoding and encoding steps that make the image resize gamma aware. Select the version you want to see from the 'Version' list in the Edit List.

VIDEO: Gary Fong on sRGB vs. AdobeRGB - don't use AdobeRGB until you listen to this first

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