[cairo] MIPMAPPING cairo.
spitzak at thefoundry.co.uk
Wed Oct 15 13:13:50 PDT 2008
Frédéric Plourde wrote:
>> Are you sure this bilinear sample is correct? It looks far worse than
>> anything I have seen. Looks more like the image was scaled to 50% and
>> the binlinearly scaled up. The current algorithim only fails if the
>> scale is less than 60% or so.
> Mhh.. yep, pretty sure. What's happening maybe is that the source image
> "http://img58.imageshack.us/img58/8669/src1231x1504np1.png" gets
> automatically resized in FF3 (and other browsers ?), but is really
> bigger than it seems. So, we're really talking about downscaling with a
> large factor.... which kills text image as you've seen.
The image is named 1231x1504to840x1026 which implies to me the
horizontal scale is 840/1231 = .68237... and the vertical scale is
1026/1504 = .68218...
It certainly looks to me like this image is a much smaller one that has
then been blown up larger:
> We already have those specific filters in Cairo, that you're talking
> about... those are FAST, GOOD and BEST. right now, we're defaulting to
> GOOD (which leads to plain bilinear downscaling), but if you're playing
> with the little cairo_downscale.c program attached to last email, you'll
> see that I'm targetting filter BEST for that.
Thanks. Carl corrected me as well. I was confused because your code had
an enumeration list at the start which did not include FAST/GOOD/BEST. I
did not realize it was just for the test program.
> Anyway, mipmapping is good, as we all know, for animation-like series
> of redrawings. That's where it wins... if not, the pyramid-building step
> overhead is so large that we certainly DON'T want to use mipmapping for
> one-shot scalings ! That's why a simple yet very nice box filtering
> algorithm (written by jeff muizelaar) is on its way to be reviewed here
> within the next few days.
The other one I would like to try is integer-sized box filtering
followed by the bilinear filter. The idea is to reuse the XRender code,
but get better down-scaling. And there would be a slight amount of
caching for similar scales.
Bill Spitzak, Senior Software Engineer
The Foundry, 618 Hampton Drive, Venice, CA, 90291, USA
Tel: +1 310 399-4555 * Fax: +1 310 450-4516 * Web: www.thefoundry.co.uk
The Foundry Visionmongers Ltd * Registered in England and Wales No: 4642027
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