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Old 28th March 2020, 23:54   #16  |  Link
poisondeathray
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Join Date: Sep 2007
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UHD YV12 1152 frame , fairly high scene complexity with foliage, people, movement

Spline16Resize => 720x480p23.976 . Did not compensate for colormatrix or anything else. This is the new source "orig"

Encoded x264 --qp 1 --keyint 1 --tune psnr

Import qp1_intra version into Resolve, matched all import/export settings. Check marked retain sub black and super white on export (this clip has some since it was a native camera shot)

Calculated per frame metrics, but I didn't plot it out, I'm just posting the averages . FFmpeg psnr

self test check orig vs. orig
lossless

x264_qp1_intra vs. orig
PSNR y:68.087383 u:67.117369 v:67.088122 average:67.733770 min:67.343042 max:68.028963

ConvertBits(8).ConvertToYV12(chromaresample="point") vs. orig
PSNR y:67.782155 u:65.525216 v:66.421621 average:67.082155 min:65.246296 max:67.911099

ConvertToYUV420(chromaresample="point").ConvertBits(8) vs. orig
#In theory 10bit downsample before converting to 8 is better, but it doesn't matter when you're just dropping samples with "point", it should with other kernals
PSNR y:67.782155 u:65.525216 v:66.421621 average:67.082155 min:65.246296 max:67.911099

z_convertformat(pixel_type="YV12", resample_filter="point", resample_filter_uv="point") vs. orig
PSNR y:53.656829 u:66.398999 v:66.530673 average:55.305442 min:53.734979 max:57.186774


There is some loss , but PSNR Y,U,V > 65 is pretty good . Minus 1 or 2 db per channel vs. the qp1_keyint1 input into Resolve . You expect some loss because of the internal YUV=>RGB=>YUV conversion in resolve, in addition to, and separate from the subsampling/upsampling

Using long GOP, you expect that up/down pattern in those charts, especially with b-frames using default I/P/B ratios. Maybe try repeating with intra

Maybe a big problem with zimg Y plane 10bit => 8bit conversion. A 12-13db PSNR delta is massive. I have a feeling user error somewhere but I repeated results with vapoursynth version , same values. I'll recheck everything, but on that colored text clip it was lower than internal AVS too.

Last edited by poisondeathray; 29th March 2020 at 00:00.
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