On Sun, Aug 2, 2009 at 7:49 PM, SHIRAKAWA Akira

> Martin Nordholts wrote:
> > Does anyone see any problems with using CIE LCH instead of HSV for these
> > layer modes? We can ignore backwards compatibility issues for now.
> I very rarely use layer modes (and I'm not a GIMP hacker so I'm probably
> missing something), but if using internally CIE LCH for image processing
> instead of HSV leads to more correct results, then I wouldn't see any
> reason to not use it.
> Except for the final results, will there be any change at a user
> interaction level? Or any practical drawback resulting from this?

LCH processing is definitely slower than HSV or HSL (whether optimized or
not), so this may have an impact on display update speed (and consequently
on user experience)

There are a few different ways of applying a 'Color' like operation, varying
in quality and speed.
LCH is certainly the best quality, Yiq is lesser quality but faster, HSL is
even lesser quality and very fast, HSV is the fastest (but so inaccurate
it's laughable)

Since GEGL provides a number of operations that are inherently expensive (eg
bilateral-filter), it may be worth considering the idea of graphs with
quality controls built in. For example, while you are painting on your Color
layer, it switches from paint application using LCH to Yiq (which is a nice
compromise and has been used for heavy-duty tasks with good results -- see
When you stop painting, it updates with the actual LCH results.
This would allow more responsive painting (and could also be applied to
paint modes)

Martin: I have made use of GIMP Value mode in the esoteric kind of way you
mention. I agree it is not worthwhile to support such uses (imo more like
abuses -- this kind of use is really begging for the use of PIL or NumPy on
a chunk of image, not the application of an image *editor*)
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