Revise premultiply #2120
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Revise premultiply #2120
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we actually test vipsthumbnail --linear on an RGBA image, which should catch everything, hopefully
for compat in thumbnail behaviour
kleisauke
reviewed
Mar 4, 2021
Co-authored-by: Kleis Auke Wolthuizen <github@kleisauke.nl>
…revise-premultiply
allow this case: vipsthumbnail k2.jpg --export-profile cmyk for an image with no embedded profile
…revise-premultiply
|
Profiling suggests the unpremultiply operation might be ~17% slower with this change. Using callgrind to unpremultiply a 6MP RGBA image with code compiled using gcc 9.3.0 and Before: After: Would the following diff be functionally equivalent? --- a/libvips/include/vips/util.h
+++ b/libvips/include/vips/util.h
@@ -91,11 +91,7 @@ vips_recip( double x )
{
static const double epsilon = 1e-10;
- int sign = x < 0.0 ? -1.0 : 1.0;
-
- return( sign * x >= epsilon ?
- 1.0 / x :
- sign / epsilon );
+ return 1 / VIPS_CLIP( -epsilon, x, epsilon );
}If so, that's only 8% slower: |
it wasn't really necessary, and it was rather slow
|
I removed the recip thing -- it wasn't really necessary, and it was slower than I expected. Thanks for the speed check! |
lovell
approved these changes
Mar 5, 2021
|
\o/ good stuff, thanks! |
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This PR revises unpremultiply (again), and tries to simplify thumbnail a bit. It fixes resizing RGBA images in scRGB space, and hopefully doesn't regress an earlier RGBA resize issue. There's a test as well, to try to stop this happening again.
Background: #1941
Related issue: #1675