[argyllcms] Re: Kick-start with collink

  • From: <robert@xxxxxxxxxxxxxxxxxx>
  • To: <argyllcms@xxxxxxxxxxxxx>
  • Date: Thu, 17 Jul 2014 13:44:57 +0100

Graeme wrote

<<I really need more feedback to add anything else or change how this works
- ie. some examples in which this works poorly, and in which a different
statistical approach might work better.>>

Hi Graeme,

I've done a few tests and the results from one set is available here:

The profiles are in the zip file - however you will need Photoshop to
examine the results.

Just to summarise: what I did was to do 3 tests with 2 profiles:
A. Argyll-generated profile using colprof (test profile with only 700
B. Canson-supplied profile.

The tests were as follows, on an Image in ProPhoto:
1. Convert the image to the destination profile using
tiffgamut/collink/cctif (windows .bat and perl script are in the zip file).
2. Convert the image to the destination using Perceptual with BPC (in
3. Convert the image to BetaRGB with Relative Colorimetric, followed by
Perceptual conversion to destination (all in Photoshop).

The converted images were then converted back to ProPhoto using RC (I
checked carefully that there was no perceptual change in the conversion back
to ProPhoto).  The image in the zip file has all of these images in layers,
plus the original. You can toggle the layers manually, or use the Layer Comp
which is a bit easier.  Also, toggling the group masks on and off helps the

My conclusion is as follows (on this image, but also on another image which
gave quite similar results):

A1: (Argyll Profile -cctiff). Very good, with the OOG oranges/yellows being
desaturated a bit, slight loss of contrast and the yellows shifted slightly
towards green.
A2: (Argyll Profile -Photoshop). Very bad. The whole image is lightened and
A3: (Argyll Profile -2Step). Very good. OOG oranges/yellows brightened,
slight loss of contrast, but quite acceptable.
B1: (Canson Profile -cctiff). Not great. Image is generally desaturated in
the yellows and greens.
B2: (Canson Profile -Photoshop). Good, but the yellows are brightened
considerably, slight loss of contrast.
B3: (Canson Profile -2Step). Very good. Same as A3. A3 and B3 appear

So overall, the cctiff approach seems very good providing the print profile
was generated using colprof.  The perceptual mapping in Photoshop using the
colprof profile is bad. The perceptual mapping in Photoshop using the Canson
profile is OK. The 2-step approach is very good with both the Canson and
colprof profiles.

The one missing test here is a 2-step test with the perceptual mapping using

Based on these tests (very limited, I know) I would favour either the 2-step
approach or using cctiff etc., with a colprof-generated print profile.  I
would be very careful before using a Perceptual mapping in Photoshop using a
colprof-generated profile (at least not with this 700-patch profile!).

I would also be quite encouraged towards using a smaller working space than
ProPhoto :).

I hope that helps.


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