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Author Topic: ICC profiles not supporting linear curve?  (Read 2833 times)

torger

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ICC profiles not supporting linear curve?
« on: December 12, 2013, 02:07:07 PM »

I've experimented a bit with ICC profile selection and input tone curves in Capture One, mainly with various Leaf backs.

I've noted that you can change tone curve while the ICC profile remain the same, and there's no strong indication on how you should match them, although it's likely that a "Portrait" ICC should be matched with a "Portrait" curve of course :-), but the naming is not always that way. As tone curves affect color (I'm assuming C1 applies the tone curve in RGB space) this means that color will get distorted if you don't use the tone curve for which the ICC profile was designed.

And yes, I've noted on one test image that when I changed from portrait curve to linear, the shadowy parts of the face got a greenish cast. I traced this cast to the cLUT conversion, and thus got a clear indication that the ICC profile was not designed for a linear curve.

I've search the docs to find a description of how to actually combine ICC profiles and tone curves but failed to do so. Anyone that has any pointer?

I'm specially interested in the linear curves as I want to output for further processing like HDR, but it seems to me that the while many cameras get a "linear" curve as a choice, it's rarely supported by a matching ICC profile, if I've figured this out properly.
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Vladimirovich

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Re: ICC profiles not supporting linear curve?
« Reply #1 on: December 12, 2013, 02:38:31 PM »

I've experimented a bit with ICC profile selection and input tone curves in Capture One, mainly with various Leaf backs.

I've noted that you can change tone curve while the ICC profile remain the same, and there's no strong indication on how you should match them, although it's likely that a "Portrait" ICC should be matched with a "Portrait" curve of course :-), but the naming is not always that way. As tone curves affect color (I'm assuming C1 applies the tone curve in RGB space) this means that color will get distorted if you don't use the tone curve for which the ICC profile was designed.

And yes, I've noted on one test image that when I changed from portrait curve to linear, the shadowy parts of the face got a greenish cast. I traced this cast to the cLUT conversion, and thus got a clear indication that the ICC profile was not designed for a linear curve.

I've search the docs to find a description of how to actually combine ICC profiles and tone curves but failed to do so. Anyone that has any pointer?

I'm specially interested in the linear curves as I want to output for further processing like HDR, but it seems to me that the while many cameras get a "linear" curve as a choice, it's rarely supported by a matching ICC profile, if I've figured this out properly.

well, use simple matrix profiles (w/o LUTs) and linear curve in a proper raw converter... certainly w/o LUTs you might get issues w/ saturated colors
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torger

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Re: ICC profiles not supporting linear curve?
« Reply #2 on: December 12, 2013, 03:28:27 PM »

well, use simple matrix profiles (w/o LUTs) and linear curve in a proper raw converter... certainly w/o LUTs you might get issues w/ saturated colors

Well, as this is the Capture One Q&A forum I thought I would get answers about how to handle C1 rather than the suggestion to use a different raw converter ;). Sure, RawTherapee is great for linear conversions and I use it a lot, but I'd like to know how to work with C1 too.
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Vladimirovich

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Re: ICC profiles not supporting linear curve?
« Reply #3 on: December 12, 2013, 03:45:46 PM »

Well, as this is the Capture One Q&A forum I thought I would get answers about how to handle C1 rather than the suggestion to use a different raw converter ;). Sure, RawTherapee is great for linear conversions and I use it a lot, but I'd like to know how to work with C1 too.
you can make matrix profile to be used in C1
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ErikKaffehr

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Re: ICC profiles not supporting linear curve?
« Reply #4 on: January 07, 2014, 07:11:54 PM »

Hi,

You can find some information in this thread: http://www.luminous-landscape.com/forum/index.php?topic=82891.msg671193#msg671193

EsbenHR who posted on the issue is a Phase One developer.

I got the impression that building ICC profiles for C1 is tricky.

Best regards
Erik
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