Are my images Green?

Started 5 months ago | Questions thread
MiraShootsNikon
Contributing MemberPosts: 661Gear list
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Excellent Test, Unexpected Results
In reply to Robin Casady, 5 months ago

Robin,

Good test--with, at least for me, unexpected and confusing results. That's good for discussion, for sure.

Of the test scenarios you ran, I found your last most intriguing. I don't understand how you can have gamut warnings if you shoot and process in sRGB and then output in sRGB. Let me unpack that statement a bit.

It may be that there are colors beyond the sRGB gamut that your RAW data might have represented in a broader color space. But if you shoot / process your RAW in sRGB, you'd never know it (beyond just eyeballing color that appears "flat")! Or have I got that wrong?

Here's my hunch: there's a problem in your test methodology. In all three cases, when you bring your RAW into Lightroom, you're working with / looking at the ProPhoto RGB articulation of your photograph and then converting that articulation to its direct equivalents in a different space. You're never actually seeing the native sRGB (or AdobeRGB) articulation of RAW data in Lightroom.

As far as I know (again, I could be wrong), you can't tell Lightroom to show you RAW in sRGB (or in AdobeRGB, or in any other gamut). You can only set Lightroom to output your results in other color spaces (e.g. when you send a frame to Photoshop or an external editor, or when you export). Or you can use soft proofing and see where pushing your ProPhoto RGB articulation into other color spaces (Adobe RGB, sRGB, your monitor's color gamut, your printer's color gamut) might result in clipped colors. But you're always looking at the ProPhoto articulation of color, even if some of those colors are clipped by relative colorimetric conversion to your monitor's gamut, etc.

To really compare the various scenarios, here, you'd need to actually see a smaller gamut's articulation of color. So here's an alternate test methodology:

(1) Shoot an Adobe RGB JPEG and convert it to sRGB (using a relative colorimetric approach)

(2) Shoot an sRGB JPEG. Leave it in the sRGB color space.

Compare.

Again, I might have this all bass-ackwards, but I really think you can't "set" Lightroom to show you RAW in sRGB or AdobeRGB--you can only tell it to output (or proof) its native ProPhoto RGB articulation to other spaces via a relative colorimetric approach.

And, good test--again, very thought-provoking.

Robin Casady wrote:

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.

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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