FreeLists / argyllcms / [argyllcms] Re: relativ volume of gamut -- vrml comparison?

[Klaus Karcher <lists@xxxxxxxxxxxxxxxxx>]

Klaus Karcher wrote:
> I am also not aware of a tool with such functionality (some can compute 
> gamut volumes, but not intersections). But you might be interested in 
> this simple command line tool: <http://www.qhull.org/> It can compute 
> e.g. the volume of the convex hull of a point cloud.
I couldn't stand trying this by myself ;-)

Here's what I did:

1.) I created a test image with timage:
timage -t timage_t_200.tif

2.) I converted it with cctiff from sRGB to ISOcoated_v2_eci relative 
colorimetric to get the intersection of the two gamuts:
cctiff -ir ~/Library/ColorSync/Profiles/sRGB.icc -ir 
/Library/ColorSync/Profiles/ISOcoated_v2_eci.icc timage_t_200.tif 
timage_t_200_sRGB_inters_iC2_r.tif
3.) I used tiffgamut to create a .gam file from it
tiffgamut -ir /Library/ColorSync/Profiles/ISOcoated_v2_eci.icc 
timage_t_200_sRGB_inters_iC2_r.tif
4.) I created gamut files for sRGB an ISOcoated in a similar way (this 
can also be done directly with iccgamut)
Now I have 3 gamut files:

timage_t_200_iC2r.gam
timage_t_200_sRGBr.gam
timage_t_200_sRGB_inters_iC2_r.gam

5.) I tweaked the gamut files with BBEdit to get the format necessary 
for qhull (first line: number of dimensions, second line: number of 
points, line 3... the points (without line numbers). This can also be 
done by a stream editor like sed.
6.) I used qhull to compute their Volumes:

qhull s FA <timage_t_200_sRGBr.points
[...]  Total volume:       626882.53

qhull s FA <timage_t_200_iC2r.points
[...]  Total volume:       476378.77

qhull s FA <timage_t_200_sRGB_inters_iC2_r.points
[...]  Total volume:       421367.74

Result: the intersection of sRGB and ISOcoated_v2 is equivalent to
67.2% of the sRGB volume or 88.4% of the ISOcoated_v2 volume.

In other words 11.6% of the colors representable in ISOcoated_v2 aren't 
reperesentable in sRGB and 32.8% of the colors representable in sRGB 
aren't reperesentable in ISOcoated_v2 (relative colorimetric).
Klaus