why does color saturation change with exposure?

Eric Hiss said:

No but when you finally get your own camera (your 1st post here states you don't have one and this request is your 2nd and last post) you can easily test this out yourself.

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Eric
in the post you're reffering, Gabor is stating that he does not have the camera involved in the thread, not that he doesn't have any…
In the same post he states that he's a pixel peeper, maybe he has a good knowledge that could help you to understand the issue you're talking about in this thead… who knows?

this request is your 2nd and last post

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and then? is that a reason for not answering the request?

I do understand and completely agree that there could be a lot of good reasons not to attach or send a raw file… (client shot, commercial, special technics used you want to keep confidential, etc.) but the reasons you give here are not good enough for me and not very fair toward Gabor…

Nicolas,
Your post is coming through as double.

I stand by my comments. The requester appears to be only asking for self satisfying reasons, and didn't even say please.

Eric Hiss said:

Nicolas,
Your post is coming through as double.

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Thanks, deleted one…

Eric Hiss said:

I stand by my comments. The requester appears to be only asking for self satisfying reasons, and didn't even say please.

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Well, the initial post of this thread contained

What's happening - shouldn't the two paths result in the same image? I'm just wondering why they are not. Anyone know what's going on?

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What kind of help are you expecting? Without being able to reproduce the effect, one can only speculate. Reproducing the effect requires having the raw images and knowing the exact adjustments in ACR. Furthermore, a low-level analysis of the raw data is quite difficult without actually having it.

Anway, good luck.

Gabor,
If you read the thread you will see that I already got a satisfactory answer from Colleen. Don't need any further info. There is no more speculation, however I encourage you to experiment to your hearts content with your own images.
Eric

Eric Hiss said:

Okay I have always heard that with digital that expose to the right then correct in RAW conversion is the proper way to manage digital capture, however when this is done the resulting images may have nice shadow detail but are less vibrant. If you expose to the left (but not to the point of clipping the shadows) then push up the image exposure in RAW then you get a much more vibrant image.

What's happening - shouldn't the two paths result in the same image? I'm just wondering why they are not. Anyone know what's going on? I've seen this now with both Flexcolor and lightroom RAW conversion tools. Btw - I am working with Leica DMR files on images that had plenty of DR to spare on both ends. Could have exposed +- 2 stops either way and still captured all the data without clipping.

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In the RAW data, the only difference is the amount of noise (and technically, the number of levels per stop, but that advantage is completely obscured by noise). If the exposure slider in your converter isn't exactly reversing the exposure, then that exposure slider is not a true linear scaling slider, and in my experience, most aren't.

Eric Hiss said:

What's happening - shouldn't the two paths result in the same image? I'm just wondering why they are not. Anyone know what's going on? I've seen this now with both Flexcolor and lightroom RAW conversion tools.

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In the case of Lightroom, the answer could lie in the 'blacks' slider. It defines a constant amount that is subtracted from all channels before the exposure slider is applied.

At its default setting of 5, it could easily explain the phenomenon you are seeing. If you overexpose and pull back in processing, you effectively get a lower value, leading to less saturated colors. If you underexpose and push in processing you effectively get a higher value, leading to more saturated colors.

Try setting the blacks slider to zero and see whether the problem disappears.

As an aside, to me this indicates that the blacks slider is serving two roles, and it seems misplaced for one of them. The first role is flare reduction. That should indeed be done in the initial stages of the pipeline, but the default value should probably be zero. The second is a black level control for the output-referred image with a default value that corresponds to the current default of 5. The latter should really be combined with the tone curve stage, IMO.

Simon

PS - I just noticed that this thread has been sleeping for a couple of months. I figure the OP may not be on this anymore, but as my answer would still be valid, I'll leave it here.