Created attachment 57657 [details] different anti aliasing methods Version: unspecified (using KDE 4.6.0) OS: Linux When looking at a huge picture (a screenshot of my desktop: 7126x1200) in different formats (here: JPEG and PNG) you can see differences in the anti aliasing when those are set to fit the screen. The JPEG is scaled smoothly (using lanczos?) while the PNG shows pixelation, especially visible on the desktop icon names. Reproducible: Always
JPEG scaling is done by decompressing a lower resolution, which is automatically smoothed because of the way JPEG works. For example, when loading a 1024x1024 image at a size of 128x128 pixels, each pixel in the scaled image is the computed average of a block of 8x8 pixels from the original image. The smooth scaling algorithms in Qt only use 4 (2x2) pixels to compute each pixel of the scaled image, so it looks worse than JPEG. This also means the "bug" can only been seen when the scaling factor is smaller than 1:2. I doubt a viewer should use a (much slower but) higher quality downscaling algorithm than what is offered by Qt. Maybe it could optionally use QImageBlitz, which has some 9- and 25-point filters, or it could use multiple downscaling steps when the scaling factor is less than 1:2. A good way would be to iteratively half the image size using [1], then as a last step use the Qt smooth scaling algorithm to get the final scaled size. [1] http://labs.qt.nokia.com/2009/01/20/50-scaling-of-argb32-image/
Okay, just a minor thing. Thanks for the info, didn‘t know. Feel free to close as invalid or whatever. Or leave it open if you wish to.
Updated link: http://blog.qt.io/blog/2009/01/20/50-scaling-of-argb32-image/
Should we close this, or is there anything we can reasonably do here?
As per Nate's Comment 4 can this now be closed or is further work needed?
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This bug has been in NEEDSINFO status with no change for at least 30 days. The bug is now closed as RESOLVED > WORKSFORME due to lack of needed information. For more information about our bug triaging procedures please read the wiki located here: https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging Thank you for helping us make KDE software even better for everyone!