Hi On Mon, Dec 16, 2024 at 11:40:50AM +0100, Niklas Haas wrote: > On Mon, 16 Dec 2024 01:50:20 +0100 Michael Niedermayer > <mich...@niedermayer.cc> wrote: > > Hi Niklas > > > > On Wed, Dec 11, 2024 at 09:25:12AM +0100, Niklas Haas wrote: > > > From: Niklas Haas <g...@haasn.dev> > > > > > > In input.c and output.c and many other places, swscale follows the rule > > > of using > > > 15-bit intermediate if output bpc is <= 8, and 19-bit (inside int32_t) > > > intermediate otherwise. See e.g. the comments on hyScale() on > > > swscale_internal.h. These are also the coefficients that > > > yuv2gbrpf32_full_X_c() > > > is using. > > > > > > In contrast to this, the plane init code in slice.c (function fill_ones) > > > is > > > assuming that we use 35-bit intermediates (inside 64-bit integers) for > > > this > > > case, seemingly added by commit b4967fc71c63eae8cd96f9c46cd3e1fbd705bbf9 > > > with > > > no further justification. > > > > > > This causes a mismatch whenever the implicitly initialized plane contents > > > leak > > > out to the output, e.g. when converting from grayscale to RGB. > > > > > > Fixes: ticket #10716 > > > Signed-off-by: Niklas Haas <g...@haasn.dev> > > > Sponsored-by: Sovereign Tech Fund > > > --- > > > libswscale/slice.c | 6 +----- > > > 1 file changed, 1 insertion(+), 5 deletions(-) > > > > ultimately 32bit on teh input or output side require more than 32bit > > internally to maintain precission. > > > > if this patch makes it all match up, its ok for now but 18bit dont seem > > enough for 32bit data >
> What exactly is the design goal here? As a point of reference, here is how > many Make the user happy :) > bits you need to represent a signal to within an error that is substantially > below the threshold of human perception in all but the most extreme synthetic > test setups: > > - HDR before linearization: 14 bits > - HDR after linearization: 35 bits > - SDR before linearization: 12 bits > - SDR after linearization: 26 bits > > If we relax this to the threshold that is required for visual transparency in > (non-static) video playback, we get: > > - HDR before linearization: 12 bits > - HDR after linearization: 30 bits > - SDR before linearization: 10 bits > - SDR after linearization: 22 bits what about image material from scientific instruments ? The question here is not if a human can see it with unadjusted contrast, but the existing precission should still be preserved thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB z(9) = an object that transcends all computable functions describable in finite terms. - ChatGPT in 2024
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