x264 "Lossless" [--qp 0] question

[Treaties Of Warp]

--qp 0 is supposed to be "lossless" as I've read.

So, I can see how the following is "lossless":

x264 --preset veryslow --qp 0 --no-deblock --profile high444 --sync-lookahead 12
--no-psy --sar 1:1 --qpfile GENERATED_QP_FILE --non-deterministic --range tv
--colormatrix bt470bg --demuxer raw --input-res 720x480 --input-range tv
--input-depth 8 --fps 25/1 --output-csp i444 --output-depth 8 --output
OUTPUTFILE -

But x264 also allows specification with --qp 0, of --output-csp i422 and --output-csp i420.

So, how can i420 be lossless?

[poisondeathray]

Originally Posted by Treaties Of Warp

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So, how can i420 be lossless?

When the input file is i420, i420 can be lossless.

When the input file is i422, i422 can be lossless.

i444 would not be lossless in those cases (although you could convert it back to the original, if nearest neighbor algorithm was used to upsample and downsample back to i420)