[argyllcms] Re: Profile input white not mapping to output white

  • From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 23 Nov 2012 12:05:24 -0700

On 2012-11-23, at 9:50 AM, Ben Goren wrote:

> I just looked a bit closer, and I can only see a half-dozen pixels clipped in 
> the second green channel in patch N18, and they're all outside of the 
> BOX_SHRINK margins.

I've done a bit more experimentation, and I'm now *VERY* confident that this 
has nothing at all to do with the RAW processing and everything to do with 
something going wonky in colprof.

I've created plain flat TIFFs in various ways out of the original RAW file, 
confirmed that there's nothing weird in the TIFFs (no clipping of anything but 
the black patch, etc.), and then fed those TIFFs to Argyll, and used Argyll for 
all further manipulation. I've also used Photoshop to tag the image with the 
profile and gotten the same results.

Here's a more dramatic recent example:


That's the original file tagged with the profile. You can confirm by checking 
the RGB values of the background -- they're all 255,255,255, but they get 
turned cyan by the profile. Assign any standard generic-ish profile (such as 
sRGB) to that image and the cyan becomes white.

For reference, here's an idealized synthetically-created version of the chart. 
You can confirm at a glance that the chart itself is being accurately 


Indeed, if you do a blink comparator type of analysis between those two 
pictures, there's hardly any visible difference at all.

Here's the .ti3 file, generated from a full-sized (but cropped) 16-bit TIFF of 
the (untagged) top image:

Attachment: 706C8559.ti3
Description: Binary data

Here're the two most relevant lines from that file:

 #     XYZ_X        XYZ_Y       XYZ_Z     RGB_R    RGB_G    RGB_B  STDDEV_R 
I13  8.7720e-03  8.5310e-03  8.8570e-03  0.52812  0.49257  0.47701  0.19195  
0.17432  0.14688 
N18 94.683      98.339      81.005      53.085   53.987   52.269    6.8720   
6.6649   6.7166

I13 is the light trap I described earlier, and N18 is a bit of Teflon thread 
seal tape. The latter is only barely above 50%, with a looooooong way to go 
before clipping.

And here's the profile by itself, created by colprof without any options:

Attachment: 706C8559.icc
Description: Binary data



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