[argyllcms] Re: Need help interpretating results of camera profiling

  • From: Bernard <bdebreil@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sun, 22 Jun 2014 01:18:27 +0200

Ben Goren wrote:
On Jun 20, 2014, at 2:03 AM, Bernard <bdebreil@xxxxxxxxx> wrote:

I will therefore try to do adjust WB and L (L a b) on the exported tiff image 
(in the color working space), not on the raw image in linear RGB absolute 
colorimetrics. But Pascal De bruijn, in his topic on camera color profiling 
from june 2010 using Darktable and Argyll, states that WB and Lightness of the 
brightest spot should be done prior to exporting

As I describe here:


you want a two-step process.

First, you create a matrix profile from a linear, gamma 1.0, UNIWB development 
of the RAW file. You then query that profile to find the white point; you tell 
your RAW developer to use that as your white point and, in so doing, normalize 
white balance and exposure both at the same time. Finally, you develop the RAW 
file with that white point and whatever other parameters you want, and generate 
your profile from that development
I went as far as getting the RGB values that would correspond to L a b = 100,0,0 using xicclu: I got 96.52 233.78 177.57. But none of the raw developers that I use in Ubuntu Linux allow me to define a white point by its RGB numbers. With Darktable, you can only define a white point using the spot technique and, if there is a way around, I have not found it so far. Ufraw doesn't do any better. I have tried to enter those RGB figures for the above defined white point, as the multipliers in white balance settings... I didn't really think that it would work, but I tried anyway... it didn't work. Dcraw -r 96.52 233.78 177.57 233.78 did not send any warning or error message ; it did work using ratios to the first entry, and the output tiff file appeared awfully green. In Darktable, you can't enter any figure for WB multipliers, other than on the interval 0-8 ; working out with ratios didn' work any better than with dcraw. If you think that there is a way around, I am willing to test it... but I don't have any MSWIN installation other than an old XP on a very old laptop and no Adobe Photoshop available. So I can only use Darktable, Ufraw, and maybe RawTherapee... that I haven't tested yet.



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