On 11/11/2014 11:45 AM, Gary Aitken wrote:
On 11/11/14 08:15, Elle Stone wrote:

So the important question is:

*What copyrighted or otherwise test images GIMP users might have
downloaded from the internet and found useful, and *what kinds of
test images GIMP users might have already put together, *for what
particular testing purposes.

The things I find most useful are the following:

1. Peoples' faces.  Important here is a wide selection of ethnicities,
    such as white, asian, african, latino.  It would be useful to have
    individual images; and combination images with the extremes (e.g.
    white, african, and wedding dress in the same image).  In the
    african group, a wide range from very black to brown.

Despite the plethora of CC- and public domain images, finding suitable test images is harder than one might think. It's obvious that a lot of time and thought went into Nicolas Robidoux's collection (http://www.imagemagick.org/download/image-bank/16bit840x840images).

In particular, it's not easy to find faces that were properly white-balanced and haven't been "in-camera jpeg processed" to have saturated colors and dark shadows.

Maybe Pat David (and other GIMP users) could suggest some good face images that were shot raw, preferably in full spectrum lighting (daylight, direct sunlight, high quality studio lighting, etc), and properly white balanced, that could be release under a suitable license?

2. Highly saturated from the natural world -- birds and flowers, for
    example.  I may have a few birds of use.  Others may well have
    better images.

Raw files of such images from a variety of cameras would be very good to have.

3. Color gradients and ICC targets.
    In this category I would find useful a chart specifically designed
    to show the boundaries of different well-known colorspaces, such
    as sRGB, AdobeRGB, and ProPhoto.

Hmm, ArgyllCMS can be used to relate actual image colors to the boundaries of any given RGB working color space, and also to compare different RGB working space color gamuts. Are the images on this page sort of what you were thinking of?



  If the chart had an outline of
    the colorspaces as separate .xcf layers it would be great.  It
    might be useful to have layers for some printers as well.

The thing is, color gamuts are 3-dimensional, so 2D charts only tell part of the story. http://brucelindbloom.com/index.html?WorkingSpaceInfo.html has great interactive tools for comparing color spaces. Click on the 3D Gamut Viewer link.

Also there is the related question of how much any give RGB working space overlaps with real-world colors as seen by the mythical average human. Lindbloom's chart indicates that ProPhotoRGB, for example, contains a lot of imaginary colors and also holds almost all real colors, whereas sRGB has no imaginary colors but only holds about 35% of all real colors.

Also see this Lindbloom page for a comparison between ProPhotoRGB and real world LAB colors as normally encoded by imaging software:

I think what you are asking about might fall into the category of better soft-proofing tools. Right now GIMP's softproofing is pretty much only what's available from LCMS, which sadly doesn't deal with "real vs. imaginary" and also does a terrible job with linear gamma working spaces (not relevant to 8-bit GIMP, but very important for high bit depth GIMP).

A test image image that shows more or less finely granulated colors spanning the full range of real world colors would be *very* nice to have, but I don't know how to make such an image. Lindbloom does supply Lab Gamut test images, but the license is restrictive (see http://brucelindbloom.com/index.html?ProfileEvaluation.html).


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