This image uses the modular encoding with a very simple prediction tree.
It also makes use of two features: upsampling (x2 factor) and a
non-standard bit depth (10 bits). The file has been generated on
https://jxl-art.surma.technology/ , with the following input:
Width 64
Height 64
Upsample 2
Bitdepth 10
if N > 300
- NE -6
- W 6
This tests that we can successfully parse the "everything" TVG files,
which make use of every feature in TinyVG.
Test files taken from https://github.com/TinyVG/examples (MIT).
This just works at the moment after e19892a099, but if we ever do
the FIXME in ColorIndexingTransform::transform(), this test will
remind us to think of this case there too.
catdog-alert-13-alpha-used-false.webp is identical to
catdog-alert-13.web but with the byte at offset 0x2a changed from
0x10 to 0x00 -- that is, the bit in the VP8L header that stores
`is_alpha_used` is cleared.
See the commit message of e19892a099 for more information.
Two files are used both as test inputs for the webp decoder test and
for the icc profile test.
Use redundant copies of these two files for the two usecases, since
different parts of the files are used in both tests (and we could
remove the unneeded parts later).
simple-vp8l-alpha-used-false.webp is a copy of simple-vp8l.webp,
with the byte at offset 0x18 changed from 0x10 to 0x00 -- that
is, the bit in the VP8L header that stores `is_alpha_used` is cleared.
We would already allocated a BGRx8888 instead of a BGRA8888 bitmap,
but keep actual alpha data in the `x` channel.
That lead to at least `image` still writing a PNG with an alpha channel.
So explicitly set the alpha channel to 0xff when is_alpha_used is false,
to make sure all consumers of decoded lossless webp data have behavior
consistent with other webp readers.
In practice, webp encoders usually don't write files that have
`is_alpha_used` set to false and then write actual alpha data to their
output. So this is rarely observable. However, for example for
lossy+ALPH webp files, the lossless webp used to store the ALPH channel
has `is_alpha_used` set to false and all channels but green are 0
(since the lossless green channel stores the alpha channel of a
lossy+ALPH webp). So if we dump such a bitmap to a standalone webp
file (e.g. with the temporary debugging code in fc3249a1ca),
then without this commit here, `image` would convert that webp to
a fully transparent webp, while other webp software would correctly
display the green image with opaque alpha.
I opened smolkling.webp in Photoshop, added a layer mask with a vertical
gradient, replaced the leftmost column with completely transparent
pixels (because the leftmost column is vertically predicted with the
horizontal filter too), and saved it as webp. That wasn't enough to
get a horizontal filter for the ALPH chunk though, so I also ran
cwebp \
-alpha_filter best \
smolkling.webp \
-o Tests/LibGfx/test-inputs/smolkling-vertical-alpha.webp
That did the trick.
I opened smolkling.webp in Photoshop, added a layer mask, and
scribbled a shape vaguely looking like the letter "C" on it.
I then saved it as a lossy webp and that was enough to end up
with filter method ¯\_(ツ)_/¯
I opened smolkling.webp in Photoshop, added a layer mask with a
horizontal gradient, and saved it as webp. That wasn't enough to
get a horizontal filter for the ALPH chunk though, so I also ran
cwebp \
-alpha_filter best \
smolkling-ps.webp \
-o Tests/LibGfx/test-inputs/smolkling-horizontal-alpha.webp
That did the trick.
(Looks like doing the same with a vertical or diagonal gradient
_also_ produces a webp file with filtering_method 1, i.e. horizontal.)
Each secondary partition has an independent BooleanDecoder.
Their bitstreams interleave per macroblock row, that is the first
macroblock row is read from the first decoder, the second from the
second, ..., until it wraps around again.
All partitions share a single prediction state though: The second
macroblock row (which reads coefficients off the second decoder) is
predicted using the result of decoding the frist macroblock row (which
reads coefficients off the first decoder).
So if I understand things right, in theory the coefficient reading could
be parallelized, but prediction can't be. (IDCT can also be
parallelized, but that's true with just a single partition too.)
I created the test image by running
examples/cwebp -low_memory -partitions 3 -o foo.webp \
~/src/serenity/Tests/LibGfx/test-inputs/4.webp
using a cwebp hacked up as described in #19149. Since creating
multi-partition lossy webps requires hacking up `cwebp`, they're likely
very rare in practice. (But maybe other programs using the libwebp API
create them.)
Fixes#19149.
With this, webp lossy support is complete (*) :^)
And with that, webp support is complete: Lossless, lossy, lossy with
alpha, animated lossless, animated lossy, animated lossy with alpha all
work.
(*: Loop filtering isn't implemented yet, which has a minor visual
effect on the output. But it's only visible when carefully comparing
a webp decoded without loop filtering to the same decoded with it.
But it's technically a part of the spec that's still missing.
The upsampling of UV in the YUV->RGB code is also low-quality. This
produces somewhat visible banding in practice in some images (e.g.
in the fire breather's face in 5.webp), so we should probably improve
that at some point. Our JPG decoder has the same issue.)
I somehow added the wrong image here. 4.webp is the one described
by the comment in the test. Now test actually uses the image it
claims to use.
No behavior change.
The alpha channel of a lossy webp is always stored separately from
the (lossy) RGB data. Alpha is either compressed in a lossless webp
that stores just the alpha data, or it's stored completely
uncompressed. (But again, even if it's compressed, it's losslessly
compressed.)
This adds a test for uncompressed alpha, which I hadn't tested before.
It seems to work correctly, though :^)
I generated the test image by running:
~/Downloads/libwebp-1.3.0-mac-arm64/bin/cwebp \
-alpha_method 0 \
Tests/LibGfx/test-inputs/extended-lossless.webp \
-o Tests/LibGfx/test-inputs/extended-lossy-uncompressed-alpha.webp
This image covers two things that aren't covered by the existing
tests, and I found it useful for testing locally. The image's license
allows redistributing it, so add it as a test case.
WebP lossless files that use a color indexing transform with <= 16
colors use pixel bundling to pack 2, 4, or 8 pixels into a single pixel.
If the image's width doesn't happen to be an exact multiple of the
bundling factor, we need to:
1. Use ceil_div() instead of just dividing the width by the bundling
factor
2. Remember the original width and use it instead of computing
reduced width times bundling factor
This does these changes, and adds a simple test for it -- it at least
checks that the decoded images have the right size.
(I created these images myself in Photoshop, and used the same
technique as for Tests/LibGfx/test-inputs/catdog-alert-*.webp
to create images with a certain number of colors.)
For the test files, I opened Base/res/icons/catdog/alert.png in Adobe
Photoshop 2023, used Image->Mode->Index Color...->
Palette: Local (Perceptive) to reduce the number of colors to 13, 8, and
3 with transparency, and 2 without transparency, then converted it back
to Image->Mode->RGB Color (else it can't be saved as webp), then
File->Save a Copy... to save a WebP (mode lossless) for every palette
size.
The image is https://quakewiki.org/wiki/File:Qpalette.png in lossless
webp format with a color indexing transform.
I've created Qpalette.webp by running
examples/cwebp -z 0 ~/src/serenity/tmp.ppm -o Qpalette.webp
built at libwebp webmproject/libwebp@0825faa4c1 (without
png support, so I first ran
Build/lagom/image ~/Downloads/Qpalette.png -o tmp.ppm
to convert it from png to a format my cwebp binary could read).
This file also happens to explicitly set max_symbol, so it serves
as a test for that code path as well.
Introduced in 2c98eff, support for non-interleaved scans was not working
for frames with a number of MCU per line or column that is odd. Indeed,
the decoder assumed that they have scans that include a fabricated MCU
like scans with multiple components.
This patch makes the decoder handle images with a number of MCU per line
or column that is odd. To do so, as in the current decoder state we do
not know if components are interleaved at allocation time, we skip over
falsely-created macroblocks when filling them. As stated in 2c98eff,
this is probably not a good solution and a whole refactor will be
welcome.
It also comes with a test that open a square image with a side of 600px,
meaning 75 MCUs.
You can generate one by using `cjpeg` with the -scan argument.
This image has been generated with the following scan file:
0 1 2: 0 0 0 0;
0: 1 9 0 0;
2: 1 63 0 0 ;
1: 1 63 0 0 ;
0: 10 63 0 0;
This type of image isn't common, and you can probably only find one by
generating it yourself. It can be done using `cjpeg` with the -scan
argument.
This image has been generated with the following scan file:
0: 0 63 0 0;
1: 0 63 0 0;
2: 0 63 0 0;
Turns out extended-lossless-animated.webp did have a loop count of 0.
So I opened it in Hex Fiend and changed the byte at position 42
(which is the first byte of the little-endian u16 storing the loop
count) to 0x2A, so that the test can compare the loop count to something
not 0.
I drew the two webp files in Photoshop and saved them using the
"Save a Copy..." dialog, with ICC profile and all other boxes checked.
(I also tried saving with all the boxes unchecked, but it still wrote an
extended webp instead of a basic file.)
The lossless file exposed a bug: I didn't handle chunk padding
correctly before this patch.
The test verifies that loading an icc file and serializing it
again produces exactly the same output as the input. That's not
always the case, but often. It requires the input file either
not having any padding or using null bytes as padding, it
requires the input file putting tag data in the order the
tag data is referenced in in the tag table, and it requires the
input file only using known tag types (which at the moment
means it only works for v4 profiles, but that part will change
in the future).
The new file p3-v4.icc was extracted from a jpeg taken by an
iPhone Mini.
icc-v4.jpg is Meta/Websites/serenityos.org/happy/3rd/bgianf.jpg.
There are a whole bunch of jpgs with v4 color profiles and I just picked
one fairly arbitrarily. It looks like a fairly standard v4 matrix
profile that in this form is also present in many jpgs taken by mobile
phone cameras. It uses parametric curves.
icc-v2.png is based on ./Documentation/WebServer_localhost.jpg since
that is the only image in the repo with a v2 color profile. It also has
all kinds of interesting and somewhat exotic tags, such as an 'dscm' (an
Apple extension to have a description of type 'mluc', since normal
'desc' is required ot have type 'desc' in v2 files -- in v4, 'desc' has
type 'mluc') tag of type 'mluc' that actually contains data in several
languages and that exercises the non-BMP UTF-16BE decoder. It's however
still also a fairly standard v2 matrix profile, which uses 'curv'
instead of 'para' for its curves ('para' is v4-only).
I converted that jpeg file to png, and cropped most of the image
data to save on file size by running:
sips -s format png --cropToHeightWidth 21 42 in.jpg --out out.png
Rather than reading files out of /res, put them in a subfolder of
Tests/LibGfx/ and pick the path based on AK_OS_SERENITY.
That way, the tests can also pass when run under lagom.
(I just `cp`d all the files that the test previously read from
random places into Tests/LibGfx/test-inputs.)
Rather than reading files out of /res, put them in a subfolder of
Tests/LibGfx/ and pick the path based on AK_OS_SERENITY.
That way, the tests can also pass when run under lagom.
