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Subject: Re: [boost] [GIL] image rescale algorithms
From: Nicolas Lelong (rotoglup_at_[hidden])
Date: 2009-09-16 15:22:08


in filters.hpp to mitchell_filter. Bicubic filter is a
> common name for bspline or photoshop style filters and
> mitchell is different.

OK, I'll take a look at this - I still need to get some proper filtering

> I think rgba32f_pixel_t is a good model for hdr pixels.
> I don't see the 0..1 range in floating point channels as limits.
> And GIL does not enforce them in any way.
> They only define a mapping between integer and floating point channels.
> In this case (rescale), clamping is an "artifact" of using integer channels
> and filters with possibly negative weights.

That's effectively a point of view of the current state of things. I'm still
not at ease with it. I believe I had problems with some algorithms that
relied on channel::max_value (being 1 for bits32f channels) and values > 1 -
but I need to look at all this before being more definitive :)

Does anyone else out there have experience manipulating HDR images using GIL

> I did some informal profiling, on a dual core machine, using the bicubic
> filter, I got this

Thanks for the information, 75-80% performance gain is not so bad for this
simple code transform ! :)


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