[argyllcms] Re: Profiling in-camera color transformation

  • From: "Pascal de Bruijn" <pmjdebruijn@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 15 Nov 2008 15:44:04 +0100

On Sat, Nov 15, 2008 at 3:38 PM, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:
> Pascal de Bruijn wrote:
>> I'm trying to create an ICC profile which imitates to color
>> transformation done by my camera.
> I'm not sure what you mean by that. Do you mean you are
> trying to profile your camera ?

Yes, but not in the normal way. Normally profiling a camera would mean you're
making a profile faithfully reproduce accurate colors.

At least for this experiment, that's not my intention.

My camera, does internally apply a color conversion. Which I can't
seem to be able
to reproduce. So I'm trying to abuse ICC profiles for that.

I want to "profile" the difference, between my raw (developed
liniearly), and the JPG
produced by my camera.

>> So I photographed an IT8 target, in RAW+JPG mode. Then I developed the
>> raw with UFRaw,
> Note that any "development" through a raw converted needs
> to be kept constant for the profile to remain valid.

Of course.

>> and converted to JPG to TIF with GIMP:
>> scanin -p -v -dipn -o IMG_4438_JPG.tif it8.cht
> This merely gets the RGB values from the image. I'm
> not sure why you are doing this given that the next command
> does the same thing as part of assembling a .ti3 file.
>> scanin -p -v -dipn IMG_4438.tif it8.cht IMG_4438_JPG.val
> This won't work. You need to provide the IT8 CIE reference values,
> the values measured from your IT8 chart with an instrument either
> by yourself, or provided by the manufacturer of the IT8 chart.

Like I said, I don't want to use the manufacturer data as a reference. But
the JPG the camera produced.

> A profile provides a model of a devices color behaviour,
> connecting the device values with the device independent
> CIE standard observer values. For an input device this
> means that two sets of information are needed for each patch,
> one being the CIE values for the patch, and the other being
> the device RGB values. scanin retrieves the latter from the raster file,
> and combines them with the CIE values you have to provide. The RGB
> values you have extracted from the raster file is not a source of
> these values.

I'm aware I'm abusing ICC in an unusual way.

But is there a way to make this work?

Pascal de Bruijn

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