On Friday 26 August 2005 15:21, Marti wrote: > On Thursday 25 August 2005 13:03, Boudewijn Rempt wrote: > > Is it possible to have lcms copy the alpha channel values when doing a > > transform? Or should that happen automatically? > > Sorry, no. lcms does *ignore* the alpha channel(s) either on input and > output. That is because lcms supports more than 1 alpha channel, and then > how tho map them in this case would be uncertain. > > In the other hand you can use the same buffer if the bps, channels and > planar organization is same. For example, if you have a "Buffer" holding > ABGR data, then you can do: > > cmsDoTransform(xform, Buffer, Buffer, npixels) > > Since lcms ignores alpha channels, this is going to work, and also solves > the multiple alpha case.
It's been a while, but we're now at a stage with Krita where having to loop by hand through all pixels to copy the alpha channel is getting rather prohibitively expensive :-(. When the display profile or colorspace isn't the same as the image profile we spend about half our cycles in cmsDoTransform, and about 30% in the alpha copy loop when loading an image and simply displaying it. -- Boudewijn Rempt http://www.valdyas.org/fading/index.cgi
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