Is Nikon Mode III really sRGB?

Started Apr 6, 2005 | Discussions thread
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digidog
digidog Veteran Member • Posts: 9,507
Why multiple sRGBs

Funny, someone just emailed me off list about this so I'm going to be lazy and cut and paste:

No camera initially produces sRGB. The RAW data is a Grayscale file. When you ask the camera to provide a file in sRGB there are two processes going on. The first is called rendering. The Grayscale RAW to color image (known as demosaicing) happens. The rendering it totally up to the manufacture to decide how they feel they are producing the most pleasing color. If you shot an identical scene with a Nikon and a Canon in sRGB, more than likely the rendering would not be the same (maybe not even close). This is much like the perceptual intent in ICC printer profiles. You can measure the same target and build two different profiles and get two different results. The manufacture has control over this rendering. Note that when you bring a RAW file into a RAW converter, this rendering process is now under your control. Just as one RAW converter might have better (or worse) default rendering, you the user can control this.

The next step is called encoding. The rendered color is encoded into a color space. This is fixed and non ambiguous. Two identical renderings will have identical encoding into a color space.

You'll note that many DSLRs have several settings for sRGB. This is just a tweak to the rendering phase of the process. Think if it like a "Velvia" setting versus an "Ekatchrome" setting whereby the manufacturers are again not trying to produce a colorimetrically accurate representation of the scene but rather the scene rendered using various bias based on that image appearing on a display. IOW, when you shoot an image of the scene, you're getting the representation of that scene as it would appear on an sRGB display.
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OK. I'm back. Note that when I say colorimetrically accurate representation, I'm talking the measured color of the scene (which includes stuff like the Illuminant, the dynamic range and so forth). Colorimetrically correct color looks pretty ugly when viewed on a display. It needs to be rendered (something called output referred) to appear as we hope the scene to appear on this output device.

What's interesting is few reviewers tell you how well the manufacturers are doing with this on the fly rendering. And if they compared the color based on RAW data, you'd have to factor in their skill on rendering using some RAW converter (which one? Each plays a role here).
--
Andrew Rodney
Author of Color Management for Photographers
The Digital Dog
http://www.digitaldog.net

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