On the surface, this trades a tiny bit of PSNR for not introducing chroma
noise into grayscale images. However, the main reason for this change is
actually motivated by a desire to avoid regressing the status quo of
duplicating swizzles being able to be commuted past dither ops.
To improve decorrelation between components, we offset the dither matrix
slightly for each component. This is currently done by adding a hard-coded
offset of {0, 3, 2, 5} to each of the four components, respectively.
However, this represents a serious challenge when re-ordering SwsDitherOp
past a swizzle, or when splitting an SwsOpList into multiple sub-operations
(e.g. for decoupling luma from subsampled chroma when they are independent).
To fix this on a fundamental level, we have to keep track of the offset per
channel as part of the SwsDitherOp metadata, and respect those values at
runtime.
This commit merely adds the metadata; the update to the underlying backends
will come in a follow-up commit. The FATE change is merely due to the
added offsets in the op list print-out.
Unfortunately, this is exceptionally difficult to handle in the general case,
when packed/bitstream formats come into play - the actual interpretation of
the offset, shift etc. are so difficult to deal with in a general case that
I think it's simpler to continue falling back to a static table of variants
for these exceptions. They are fortunately small in number.
This is the only function that actually has the ability to return an
error, so just move the pixel type assignment here and add a check to
ensure a valid pixel type is found.
This code was previously broken; since YAF32BE/LE were not included as
part of the format enumeration. However, since we *always* know the correct
swizzle for YA formats, we can just special-case this by the number of
components instead.
This patch adds format handling code for the new operations. This entails
fully decoding a format to standardized RGB, and the inverse.
Handling it this way means we can always guarantee that a conversion path
exists from A to B without having to explicitly cover logic for each path;
and choosing RGB instead of YUV as the intermediate (as was done in swscale
v1) is more flexible with regards to enabling further operations such as
primaries conversions, linear scaling, etc.
In the case of YUV->YUV transform, the redundant matrix multiplication will
be canceled out anyways.
The underlying integer type of an enumeration is
implementation-defined (see C11, 6.7.2.2 (4)); GCC defaults
to unsigned if there are no negative values like for all enums
from pixfmt.h except enum AVPixelFormat.
This means that tests like "if (csp >= AVCOL_SPC_NB)" for
invalid colorspaces need not work as expected (namely if
enum AVColorSpace is signed). It also means that testing
for such an enum variable to be >= 0 may be tautologically
true. Clang emits a -Wtautological-unsigned-enum-zero-compare
warning for this.
Fix both of these issues by casting to unsigned.
Also do the same in libswscale/format.c.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
utils.c is getting quite crowded, and I need a new place to dump a lot of
format handling code for the ongoing rewrite. Rather than bloating this file
even more, start splitting format handling helpers off into a new file.
This also renames the existing utils.h header, which didn't really contain
anything except the SwsFormat definition anyway (the prototypes for what should
have been in utils.h are all still in the legacy swscale_internal.h).
