[argyllcms] Re: Profiling between two images

On Thu, Jan 29, 2009 at 10:01 PM, Klaus Karcher <lists@xxxxxxxxxxxxxxxxx> wrote:
> Pascal de Bruijn wrote:
>>
>> Hi,
>>
>> I've more or less asked about this in the past, but I gave up on it,
>> back then...
>>
>> I have two images of an IT8 chart...
>>
>> 1. A digital camera generated JPG (white-balanced, and gamma corrected)
>> 2. A RAW file, converted to JPG (white-balanced, but not gamma
>> corrected, so it's linear RGB)
>>
>> Both images, are in fact, the same image, just stored in a different
>> way...
>>
>> I'd like to generate a profile, which would turn my nr 2 image into
>> something very close to my nr 1 image.
>>
>> Is this possible? Can anybody help me with accomplishing this?
>
> If the only difference between the images is actually the gamma, you won't
> need a profile -- a simple curve (e.g as adjustment layer in Photoshop) will
> do it. The shape of the curve is y = x^gamma where x and y are the RGB
> source and target values scaled to [0 ... 1].
>
> Also the middle control in Photoshop's Levels Adjustment (Layers) is nothing
> but a gamma correction control.
>
> If you have a matrix profile for one of the images, you can build one for
> the counterpart in Photoshop: Go to the Color Preferences and load the
> profile as your RGB working space, then select "Custom RGB" as your RGB
> working space. Photoshop will show you a dialog with the gamma, whitepoint
> and primary values of the profile. You can edit the gamma value and save
> this modified "Custom RGB" setting as ICC profile. (Don't forget to return
> to your original Color settings when you are done.

I don't have photoshop, and it's not only the gamma... The camera also does a
color transform of some sort..

Regards,
Pascal de Bruijn

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