Photoshop is not mainly a painting application, though it can be used as one.
The strength of Photoshop is in its automation, ability to integrate with all kinds of things, ability to open a hundred different formats by default, plugins, 16-bit-per-channel support, color management, work with huge files, etc etc etc.
This looks like a competitor for ArtRage or Corel Paint.
http://krita.org/faq/item/16-krita-features contains some information on the features supported by Krita, including 16 bit per channel colorspaces (including Lab, a much-vaunted Photoshop feature). Krita is also available with support for OpenColorIO, and integration into the asset pipelines found e.g. in VFX studios is part of its mission statement (support for Photoshop's file formats has been steadily increasing along the way).
You're entirely correct about Krita's focus on painting (a focus it has greatly benefited from; see also my other comment), but it turns out the kinds of foundations required by a good painting application offer utility in many use cases.
> The strength of Photoshop is in its automation, ability to integrate with all kinds of things, ability to open a hundred different formats by default, plugins, ....
This, as far as I can see, sums up Gimp very well. With its open scripting and plugin system (Python) which not only allows anyone to write simple automation scripts, but allows people like me to find importers, exporters, filetype support, scripts and plugins for free, for about anyhting thinkable.
How does Photoshop compare to the Gimp in these areas? I am aware of the differences in usability, obviously. But purely on technical grounds: is the automatability and extensability of the Gimp comparable to that of Photoshop?
The problems with GIMP, the last time I checked, were - no support for 16 bit, problems with color management, slow (photoshop is extremely optimized, and now has GPU support). Plus I hate the default UI - they need to redo it completely.
Proper 16-bit support is the big thing for the next release and it's significantly less slow since it got multithreading support in 2.8. Still slower than Photoshop, though.
The strength of Photoshop is in its automation, ability to integrate with all kinds of things, ability to open a hundred different formats by default, plugins, 16-bit-per-channel support, color management, work with huge files, etc etc etc.
This looks like a competitor for ArtRage or Corel Paint.