Are my images Green?

Started 3 months ago | Questions thread
Robin Casady
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Some Tests ProPhotoRGB to sRGB vs working in sRGB
In reply to MiraShootsNikon, 3 months ago

MiraShootsNikon wrote:

Hmm. When I compare AdobeRGB or ProPhotoRGB to sRGB, what I see is that the gamuts are all shaped differently. It's not just that ProPhotoRGB or AdobeRGB are "bigger" than sRGB in every direction--it's that they're bigger at different rates in different directions.

That would suggest to me that it's not just a question of one space being able to account for "more" or "less" color than another; rather, it would seem that the same RAW bits converted in different color spaces would articulate color with qualitative differences, based on each space's shape. If you edit in ProPhoto RGB or AdobeRGB, it's not just that there's "more color" or that each bit represents a bigger color shift in every direction--it's that the result will actually look different over the regions the two spaces share.

Taking this observation one step further: if you process your RAW in ProPhoto or AdobeRGB and then later convert to sRGB, is it true that your software "squeezes" the ProPhoto or Adobe RGB articulation into the sRGB space (i.e., compresses the "gaps" per bit) or is it the case that your software simply converts the ProPhoto or AdobeRGB articulation to the closest directly equivalent colors in the sRGB space and just clips any instance in which the ProPhoto or AdobeRGB articulation exceeds the sRGB gamut?

I think the later is what occurs, not the former.

In other words, processing RAW in ProPhoto or AdobeRGB and then converting that result, later, to sRGB gives you the ProPhotoRGB or AdobeRGB articulation of color (at least over the regions sRGB has equivalents). That is not the same thing as processing (or just shooting JPEGs) in sRGB from the start, in which case you'd only ever have the sRGB articulation of color--not just the sRGB range, but its unique articulation, too.

What I'm getting at, here, is that choice of color space seems to depend on how you ultimately want your colors qualitatively represented, not whether you want "more" or "less" color or whether you're afraid of posterization, etc. Based on what I see processing RAW, ProPhoto RGB or Adobe RGB appear to be more attractive choices for most subject material, even if you'll ultimately be converting the ProPhoto or Adobe articulation into sRGB over the range of colors they share.

But, you know, I could always be wrong and/or color blind!

This inspired me to try and see what would happen to colors with the three different paths to an sRGB web image.

  1. ProPhotoRGB to sRGB
  2. AdobeRGB to sRGB
  3. sRGB to sRGB

I set Lightroom 5.5 preferences to ProPhotoRGB. Exported the image to Photoshop CS6. Used Save for Web with conversion to sRGB enabled. The camera profile was Camera Neutral. If there is something wrong with this methodology, let me know.

ProPhotoRGB to sRGB

AdobeRGB to sRGB

sRGB to sRGB

All of the above showed gamut warnings in Photoshop before converting to sRGB. In other to eliminate gamut warnings the saturation had to be reduced to levels below what looked right. For ProPhotoRGB it was -42 saturation. sRGB required -46 saturation.

Saturation +42 ProPhotoRGB to sRGB

Saturation -44 AdobeRGB to sRGB

Saturation -46 sRGB to sRGB

Thoughts?

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Robin Casady
http://www.robincasady.com/Photo/index.html
"Get your facts first, then you can distort them as you please."
—Mark Twain

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