RE: [png-mng-implement] RE: When to do gamma/color correction

[John B. <jb...@ac...>]

From: Greg Roelofs
>Well, traditionally, that's where libraries come in--they're the middle
>ground between platform and app.  One of my hopefully-near-future mini-
>projects will be to add lcms support to libpng, which would then be a
>handy way to spread the love across lots of apps.

That's a good thing in itself, but it has limited application.  With libpng
the caller has to chose an intermediate representation, and typical
intermediate representations (e.g. sRGB) have a limited gamut, so the CMS
smashes the colours to the intermediate form (say sRGB) then the OS
rendering layer attempts to render to something with a different gamut
(anything other than a CRT in the case of sRGB).

Wide gamut intermediates avoid this, however the support for wide gamut
intermediates (e.g. 16 bit RGB with the potential to store values >1.0 and
<0.0) is even more limited than support for CMS in the OS rendering.

So what I'm saying is that the middle layer doesn't help - the support must
be in the rendering layer, either OS or window system (or both).

>there's a monster mess
>of 2D/3D/hardware/software/OpenGL/etc. trouble brewing in X land, but
that's
>not necessarily a cross-platform problem (yet, anyway).

Inevitable because problem specific solutions were implemented in the
absence of a good overall design.  My theory was that SVG might provide a
set of common capabilities which can then be bound into a single coherent
functional interface.  Since SVG and GDI+ are pretty much just a combination
of PostScript style vector drawing (linear paths only - no paths where more
than two lines join at a single point) and sampled image rendering a
functional API can probably be readily translated from one to the other.

Maybe it's a non-issue.  Most applications seem to have a whole lot of GUI
and very little content - very little rendered graphics outside the GUI
elements.  Consequently app developers are prepared to spend quite a lot of
time and code on the content, even to the extent of reinventing stuff which
could be shared in a library or the OS.  (Think about the task of rendering
even a simple diagram - say a simple Venn diagram - I would certainly be
prepared to spend a lot of time looking for a library to do this and, if I
couldn't find one, would consider generating, say, PostScript and displaying
that.)

John Bowler <jb...@ac...>