[argyllcms] Re: Calculate RAW importer profiles ?

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 27 Jul 2015 23:19:51 +1000

Adriaan van Os wrote:

My thinking is, not to use a test chart, but the existing photo library that
a photograher
has on his hard-disk and let statistics do its work to compensate for lack of
test-gamut in single photos. So, we have a JPG with a known profile and we
can convert the
JPG RGB pixel values to XYZ. And we have a raw-converter produced TIFF with
colors. So, the task is to calculate the color transform that would produce
the same XYZ
vales for the TIFF as in the JPG. That color transform then constitutes the
Profile to be
assigned to the TIFF after the raw converter has done its work. This is
repeated over many
photos and a statistical average (mean or median) is calculated. The standard
would be a meaningful value too.

That would be even more of a project. ArgyllCMS doesn't currently have any tools
to create a device to device mapping directly from device to device samples. The
underlying functions are certainly there, but new code would be needed to make
it available in the form you are after.

To use the images in a sensible way, the colors in each image would need to
be quantized. I do have an implementation for an algorithm to do this that I
created for xli (median cut quantizer), but I have never got around to creating
an ArgyllCMS tool to do that, and it would need tweaking to keep track of the
image area that the color originated from, to be able to create the
data sets.

So there would need to be two new tools created, but the fundamental drawback of
this approach would seem to be that a collection of images almost certainly
explore the full gamut, so you would be relying on the
of the mapping function to cover this up.

Graeme Gill.

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