Funny you should mention this! (And sorry for the delay, I think this got lost in the post-SIGGRAPH coma.)
I came across this again today on my side, and finally decided to make those fixed-width filters able to resize to whatever width is specified (with the default width being the "usual" one). It was just catrom and lanczos3 that were like this. Here's the PR for it: https://github.com/OpenImageIO/oiio/pull/1228 <https://github.com/OpenImageIO/oiio/pull/1228> In a practical sense, this seems to work just fine -- the results seem reasonably pleasing to my eye, and match some other software we tried. Want to give it a shot and see if it matches your expectations now? -- lg > On Aug 26, 2015, at 8:00 AM, John Haddon <[email protected]> wrote: > > Hi, > > First off, a confession. I'm not too familiar with image processing stuff, so > when I needed some resizing code for a tool I was writing, I based mine > heavily on ImageBufAlgo's resize(). Thanks for the excellent resource. > > In this tool, the user specifies both the image size and also the filter, > which led to the eventual realisation that OIIO's resize (and therefore my > homage) doesn't upsize with non-scalable filters, as demonstrated in this > invocation of oiitool : > > oiiotool --create 10x10 3 --fill:color=1,1,1 0,0,10,10 --resize:filter=catrom > 100x100 -o test.png > > It seems that when upsizing, the filter falls through the cracks between > source pixels, because the constructor for catmull-rom and lanczos filters > ignores the width, and the filter radius is therefore much smaller than the > sampling code expects. This means that much of the resized image is black > rather than the expected white. > > In my ignorance, I'm wondering what is the right thing to do here, from an > image processing perspective? Presumably I could just adjust for the fact > that the filter is created smaller than expected, and scale the lookup > locations on the way in, but is that meaningless? Are these filter types > simply not intended for upscaling? Would it be better to silently substitute > in a different filter, or perhaps to raise an error? > > Thanks in advance for any suggestions you could provide... > Cheers... > John > > > > _______________________________________________ > Oiio-dev mailing list > [email protected] <mailto:[email protected]> > http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org > <http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org> -- Larry Gritz [email protected]
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