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I have some RAW files (CR2 and NEF) captured using Canon & Nikon cameras. If I have to perform Colour balancing/Colour correction using Lightroom or Adobe Photoshop CS, would those tools give me the colour correction matrix (assuming it uses a 3x3 or 3x4 matrix to perform colour balancing of the raw image after it has been demosaiced/interpolated to RGB)

Will I be able to get the coefficients of the colour correction matrix used by the post processing tools. I need these matrix coefficients to plug in my own post processing code to see If I get similar output after colour correction or not?

Any pointers would be useful.

thanks,

-AD

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1 Answer 1

I'm 99% sure there's no way to export a colour correction matrix from Lightroom or Adobe Camera Raw, because a) I've gone through every menu in the past and not seen anything like it, and b) I believe the colour correction is more complex than a linear transform. Adobes camera colour profiles are 'twisted' which means the colours change depending on luminance to mimic changes in colour perception. I wouldn't be surprised if Adobe used other tricks as well so I don't think you'll be able to replicate the colour correction in your own code.

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When I capture the raw image using my own Camera,I take image of a Colour chart.Then I use this raw image capture, demosaic it & using a 3rd party tool, obtain a colour correction matrix, which I use in my code. But problem comes when I pick raw images available online. I do not have the correct calibrated colour correction matrix for those images/lighting conditions/sensors used to capture those images. Hence I am looking for the colour correction matrix. Do you think any other post process tool might have a chance? Do you have any further pointers as to how I can go about? –  goldenmean Apr 27 '11 at 12:33
    
The luminance dependency of the transform is interesting. Have you by any chance looked in the XMP files to see if there's anything usable in there? I don't have a LR installation right now to see. –  coneslayer Apr 27 '11 at 13:50
    
How does then Photoshop/Lightroom get information about the right colour correction coefficients when it does the post processing? I mean does it read the EXIF/Metadata present in the RAW files to decide how it's going to perform the colour balancing or how do those tools do it? –  goldenmean Apr 27 '11 at 15:44
    
The XMP file contains a reference to a camera profile which containts the colour correction information, but it's not as simple as a matrix of coefficients due to the intensity dependant component. As far as I know it ignores anything in the raw files. –  Matt Grum Apr 27 '11 at 16:20
    
Thanks. When does one get this XMP file. Does it vary for each captrued raw image file or these XMP files are stored and used by Photoshop? –  goldenmean Apr 27 '11 at 17:27

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