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artifact types:
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ringing
wave or noise like patterns around sharp edges
bad: sinc, lanczos (with high filter length)
acceptable: lanczos (with low filter length), cubic, spline
ok: area, (fast)blinear, gauss, point
blur
loss of detail / high frequency
bad: gauss with high variance
acceptable: (fast)bilinear, area
ok: others
aliasing (only downscale)
straight lines look like staircases
areas of high detail look worse
regular patterns turn into a funny looking mess (moire patterns)
bad: fast bilinear, point, gauss with low variance
acceptable: area
ok: others
blocky (upscale only)
looks like the image is made of rectangular blocks like a mosaic
bad: point
ok: others
recommendations: (based upon my personal opinion many ppl might disagree ...)
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the recommended scalers for upscaling:
fast_bilinear, point if speed is important
cubic, spline, lanczos if quality is important
the recommended scalers for downscaling:
fast_bilinear, point if speed is important
gauss, bilinear if quality is important
cubic, spline, lanczos if a sharper picture is important
note: when encoding at a limited amount of bits (not constant quantizer)
then a slightly blurred input might look better after decoding than a slightly
sharpened one, especially for lower bitrates
sws numbers / names / artifact types
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r ringing
b blurry
a aliasing (downscale only)
m mosaic (blocky) (upscale only)
-sws 0 fast bilinear bA
-sws 1 bilinear b
-sws 2 bicubic high sharpness r
low sharpness b
-sws 3 experimental ????
-sws 4 nearest neighbour AM
-sws 5 area ba
-sws 6 luma bicubic / chroma bilinear r
-sws 7 gauss low sharpness B
high sharpness AM
-sws 8 sinc R
-sws 9 lanczos long filter R
short filter b
-sws 10 bicubic spline r
Notes:
area upscale is identical to bilinear
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