Performance problem with colorspace conversion in lcms2

[Lukast dev]

Linear format is not needed for gmic.

Do you have suggestions how to implement it correctly for all possible
colorspace formats
that we currently support?

And where does this plain scaling belongs to? Pigment?

Lukas


2013/10/2 Boudewijn Rempt <boud at valdyas.org>

> On Tuesday 01 October 2013 Oct 22:15:30 Lukast dev wrote:
> > Hi all,
> >
> > I'm working on Gmic as you know and I hit performance bottleneck
> > when converting Krita layers to gmic layers and back and making the whole
> > experience for Krita artists quite slow.
> >
> > What I'm doing -- converting Krita colorspace uchar 8-bit rgba  to float
> > 32-bit rgba.
> > I found out that the bottleneck is actually in lcms2
> >
> > There is benchmark where is roundtrip conversion rgb8-float-rgb8
> > You can run it at
> > "build/calligra/krita/plugins/extensions/gmic/tests/KisGmicBenchmark
> > testConversion"
> >
> > Source:
> >
> calligra/krita/plugins/extensions/gmic/tests/kis_gmic_benchmark.cpp::testConversion()
> >
> > From the valgrind log [1] we can see that the bottleneck (98% of time)
> is in
> >
> > KoColorSpace::convertTo
> > and there in
> > cmsDoTransform
> >
> > and there it looks like it is using a lot of math pow, exp per pixel
> which
> > is of course slow.
> > For 3840x2400 image it takes 6,5 second to convert from rgba8 to rgba32
> > float on my laptop.
> >
> > I wrote this hack to convert Krita pixels from rgba8->rgba32 float:
> > http://paste.kde.org/p19eeee78/
> >
> > It takes 120 ms to convert Krita layer to gmic with this hack way, so
> it's
> > 60-times faster.
> >
> > Of course it ignores all rendering intends and profile, but I wonder if
> > there is some way to tell
> > lcms2 to do it stupidly and simply and avoid stuff like: pow, exp1 per
> > pixel and cmsEvalToneCurveFloat?
>
> I don't think so -- it's exactly what LCMS is doing. But I think that for
> G'Mic, a plain scaling of rgb u8 to rgb f32 is actually better than going
> through lcms and actually converting the colorspace.
>
> That is -- unless G'Mic needs the f32 data in linear format? If that's
> needed, you really need to use the proper profiles and let lcms do the
> conversion.
>
> >
> > [1] valgrind log
> > https://www.dropbox.com/s/wvazoys09p0ujtb/callgrind-convert-to.tgz
> >
> > Lukas
> --
> Boudewijn Rempt
> http://www.valdyas.org, http://www.krita.org, http://www.boudewijnrempt.nl
>
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