Template 2 is needed by some symbols in 0000372.pdf page 11 and
0000857.pdf pages 1-4. Implement the others too while here. (The
mentioned pages in those two PDFs also use the "end of stripe" segment,
so they still don't render yet.
We still don't support EXTTEMPLATE.
This extracts the bitbuffer combining code we had into a new function
composite_bitbuffer() and adds the following features:
* Real support for combination operators (which also lets us allow black
as background color again, even if that's never used in practice)
* Clipping support (not used here yet, but will be needed elsewhere
soon)
We're going to need this for text segment handling.
No behavior change.
I created this file using `jbig2` (see below for details), but as
far as I can tell `jbig2` does not produce spec-compliant files:
1. It always writes to 0s for the run lengths that specify how
many symbols to export at the end of a symbol segment
2. It doesn't write any referred-to segments for text segments.
I think it's supposed to write a referred-to segment that
mentions the symbol segment the text segment refers to (?)
I locally tweaked `jbig2` to fix these two defects (*), so the image
added in this commit is correct as best I can tell. It opens fine
using `image` and `jbig2`'s decode mode, and via
`Meta/jbig2_to_pdf.py` in Firefox and Chrome. Without my tweaks,
the image decodes fine with `jbig2`, but not with any of the other
three. The image (in a pdf) does _not_ decode in Preview.app,
either with or without my local `jbig2` tweaks.
*: See the PR adding this image for my local diff.
I created the test image file by running this shell script with
`jbig2` tweaked as described above:
#!/bin/bash
set -eu
I=Build/lagom/bin/image
S=Tests/LibGfx/test-inputs/bmp/bitmap.bmp
$I "$S" --crop 232,70,120,250 -o mouth.bmp
$I "$S" --crop 135,100,100,100 -o nose.bmp
$I "$S" --crop 50,108,30,30 -o top_eye.bmp
$I "$S" --crop 60,265,30,30 -o bottom_eye.bmp
# I then manually converted those to 1bpp using Photoshop
# (Image->Mode->Grayscale, then Image->Mode->Bitmap...,
# File->Save As..., bmp) since `jbig2` gets confused by non-1bpp
# bmp files and `image` can't write 1bpp files :/
#
# (I tried `convert ${in} -monochrome ${in}-1bpp.bmp` via
# https://cancerberosgx.github.io/magic/playground/index.html
# first, but that produced bmp files that neither Preview.app nor
# `jbig2` could handle.)
#
# -HeightClass: Number of height classes
# -WidthClass: Maximum number of symbols in one height class
# -Simple means no refinement; the number after is the symbol's ID
# The 3 numbers afer `-ID` are id, y, x. The `-ID` are sorted by x.
# -RefCorner 1 means "top left".
#
# `jbig2` writes symbol and text segments as specified in the ini
# file, and then only stores the bits of the input image that aren't
# already set through symbol and text segments.
cat << EOF > jbig2-symbol.ini
-sym -Seg 1
-sym -file -numClass -HeightClass 3 -WidthClass 2
-sym -file -numSymbol 4
-sym -file -Height 250
-sym -file -Width 120 -Simple 0 mouth-1bpp.bmp
-sym -file -EndOfHeightClass
-sym -file -Height 100
-sym -file -Width 100 -Simple 1 nose-1bpp.bmp
-sym -file -EndOfHeightClass
-sym -file -Height 30
-sym -file -Width 30 -Simple 2 top_eye-1bpp.bmp
-sym -file -Width 30 -Simple 3 bottom_eye-1bpp.bmp
-sym -file -EndOfHeightClass
-sym -Param -Huff_DH 0
-sym -Param -Huff_DW 0
-txt -Seg 2
-txt -Param -numInst 4
-ID 2 108 50 -ID 3 265 60 -ID 1 100 135 -ID 0 70 232
-txt -Param -RefCorner 1
-txt -Param -Xlocation 0
-txt -Param -Ylocation 0
-txt -Param -W 399
-txt -Param -H 400
EOF
J=$HOME/Downloads/T-REC-T.88-201808-I\!\!SOFT-ZST-E/Software
J=$J/JBIG2_SampleSoftware-A20180829/source/jbig2
$J -i "${S%.bmp}" -f bmp -o symbol -F jb2 -ini jbig2-symbol.ini
"TPGD" is short for "Typical Prediction for Generic Direct coding",
and the "ON" bit turns it on. In this mode, before decoding a line,
we decode a single bit first that controls if the current line is
just a copy of the previous line. If so, the line's pixels aren't
encoded, the decoder just copies the previous line.
I created this by running
jbig2 -i Tests/LibGfx/test-inputs/bmp/bitmap -f bmp \
-o bitmap -F jb2 -ini tpgdon.ini
where tpgdon.ini contained:
-Gen -Seg 1
-Gen -Param -TpGDon 1
See previous commits in this directory for details on the `jbig2` tool.
Sadly, the TPGDON writing path in `jbig2` wasn't implemented yet,
so I had to add this. See the PR that added this commit for my
local diff to `jbig2`.
I'm somewhat confident that my change to `jbig2` (and hence the
image added in this commit) is correct because:
1. `jbig2` succeeds in converting this file to a bmp file,
while it failed without my patch (the decoding codepath in
`jbig2` does have TPGDON support)
2. Other pdf viewers display the output of
`Meta/jbig2_to_pdf.py -o foo.pdf path/to/bitmap-tpgdon.jbig2 399 400`
the same way we do
It seems to do the right thing already, and nothing in the spec says
not to do this as far as I can tell.
With this, we can finally decode
Tests/LibGfx/test-inputs/jbig2/bitmap.jbig2 and add a test for
decoding simple arithmetic-coded images.
In practice, everything uses white backgrounds and operators `or`
or `xor` to turn them black, at least for the simple images we're
about to be able to decode.
To make sure we don't forget implementing this for real once needed,
reject other ops, and also reject black backgrounds (because 1 | 0
is 1, not 0 like our overwrite implementation will produce).
This means we have to remove a test, but since this scenario doesn't
seem to happen in practice, that seems ok.
The context can vary for every bit we read.
This does not affect the one use in the test which reuses the same
context for all bits, but it is necessary for future changes.
I think the context normally changes for every bit. But this here
is enough to correctly decode the test bitstream in Annex H.2 in
the spec, which seems like a good checkpoint.
The internals of the decoder use spec naming, to make the code
look virtually identical to what's in the spec. (Even so, I managed
to put in several typos that took a while to track down.)
With this, `image` can convert any jbig2 file, as long as it's
black (or white), and LibPDF can draw jbig2 files (again, as long
as they only contain a single color stored in just a
PageInformation segment).
I extracted a pure-white jbig2 that has only a PageInformation segment
from a PDF and manually edited the bytes to reduce the bitmap size to
47x23 and to clear all unneded bits (except, in the black version,
the page color bit is set).
This allows `file` to correctly print the dimensions of a .jbig2 file,
and it allows us to write a test that covers much of all the code
written so far.
I created this by running
jbig2 -i Tests/LibGfx/test-inputs/bmp/bitmap -f bmp -o bitmap -F jb2
using the `jbig2` tool whose source code is in the zip file here:
https://www.itu.int/rec/T-REC-T.88-201808-I
(Just `make jbig2` in Software/JBIG2_SampleSoftware-A20180829/source
was enough to build it.)
As far as I can tell (cf `JBIG2_EncMain()` which always writes `1`
to the flags byte in the file header), this tool always writes files
in the sequential organization.
This is for validating that a decoder with a weak or nonexistent
sniff() method thinks it can decode an image. This should not be
treated as an error.
No behavior change.
The semantics of BGRx8888 aren't super clear and it means different
things for different parts of the codebase. In particular, the PNG
writer still writes the x channel to the alpha channel of its output.
In BMPs, the 4th palette byte is usually 0, which means after #21412 we
started writing all .bmp files with <= 8bpp as completely transparent
to PNGs.
This works around that.
(See also #19464 for previous similar workarounds.)
The added `bitmap.bmp` is a 1bpp file I drew in Photoshop and saved
using its "Save as..." saving path.
A tile is basically a strip with a user-defined width. With that in
mind, adding support for them is quite straightforward. As a lot the
common code was named after 'strips', to avoid future confusion I
renamed everything that interact with either strips or tiles to a
global term: 'segment'.
Note that tiled images are supposed to always have a 'TileOffsets' tag
instead of 'StripOffset'. However, this doesn't seem to be enforced by
encoders, so we support having either of them indifferently.
The test case was generated with the following Python script:
import pyvips
img = pyvips.Image.new_from_file('deflate.tiff')
img.write_to_file('tiled.tiff',
compression=pyvips.ForeignTiffCompression.DEFLATE,
tile=True, tile_width=64, tile_height=64)
JPEGs can store a `restart_interval`, which controls how many
minimum coded units (MCUs) apart the stream state resets.
This can be used for error correction, decoding parts of a jpeg
in parallel, etc.
We tried to use
u32 i = vcursor * context.mblock_meta.hpadded_count + hcursor;
i % (context.dc_restart_interval *
context.sampling_factors.vertical *
context.sampling_factors.horizontal) == 0
to check if we hit a multiple of an MCU.
`hcursor` is the horizontal offset into 8x8 blocks, vcursor the
vertical offset, and hpadded_count stores how many 8x8 blocks
we have per row, padded to a multiple of the sampling factor.
This isn't quite right if hcursor isn't divisible by both
the vertical and horizontal sampling factor. Tweak things so
that they work.
Also rename `i` to `number_of_mcus_decoded_so_far` since that
what it is, at least now.
For the test case, I converted an existing image to a ppm:
Build/lagom/bin/image -o out.ppm \
Tests/LibGfx/test-inputs/jpg/12-bit.jpg
Then I resized it to 102x77px in Photoshop and saved it again.
Then I turned it into a jpeg like so:
path/to/cjpeg \
-outfile Tests/LibGfx/test-inputs/jpg/odd-restart.jpg \
-sample 2x2,1x1,1x1 -quality 5 -restart 3B out.ppm
The trick here is to:
a) Pick a size that's not divisible by the data size width (8),
and that when rounded to a block size (13) still isn't divisible
by the subsample factor -- done by picking a width of 102.
b) Pick a huffman table that doesn't happen to contain the bit
pattern for a restart marker, so that reading a restart marker
from the bitstream as data causes a failure (-quality 5 happens
to do this)
c) Pick a restart interval where we fail to skip it if our calculation
is off (-restart 3B)
Together with #22987, fixes#22780.
Non-interleaved files always have an MCU of one data unit.
(A "data unit" is an 8x8 tile of pixels, and an "MCU" is a
"minium coded unit", e.g. 2x2 data units for luminance and
1 data unit each for Cr and Cb for a YCrCb image with
4:2:0 subsampling.)
For the test case, I converted an existing image to a ppm:
Build/lagom/bin/image -o out.ppm \
Tests/LibGfx/test-inputs/jpg/12-bit.jpg
Then I converted it to grayscale and saved it as a pgm in Photoshop.
Then I turned it into a weird jpeg like so:
path/to/cjpeg \
-outfile Tests/LibGfx/test-inputs/jpg/grayscale_mcu.jpg \
-sample 2x2 -restart 3 out.pgm
Makes 3 of the 5 jpegs failing to decode at #22780 go.
I opened Base/res/graphics/buggie.png in Photoshop, converted it
to U.S. Web Coated (SWOP) v2, flattened the image so we don't have
CMYK with alpha, and saved it as a jpeg (with color profile embedded).
When present, the alpha channel is also affected by the horizontal
differencing predictor.
The test case was generated with GIMP with the following steps:
- Open an RGB image
- Add a transparency layer
- Export as TIFF with the LZW compression scheme
This tag is required by the specification, but some encoders (at least
Krita) don't write it for images with a single strip.
The test file was generated by opening deflate.tiff in Krita and saving
it with the DEFLATE compression.
Type 2 <=> One-dimensional Group3, customized for TIFF
Type 3 <=> Two-dimensional Group3, uses the original 1D internally
Type 4 <=> Two-dimensional Group4
So let's clarify that this is not Group3 1D but the TIFF variant, which
is called `CCITTRLE` in libtiff. So let's stick with this name to avoid
confusion.
Images with a display mask ("stencil" as it's called in DPaint) add
an extra bitplane which acts as a mask. For now, at least skip it
properly. Later we should render masked pixels as transparent, but
this requires some refactoring.
We now allow all subsampling factors where the subsampling factors
of follow-on components evenly decode the ones of the first component.
In practice, this allows YCCK 2111, CMYK 2112, and CMYK 2111.
I created a 16-bpp RGB file in Display P3 in photoshop, filled it
with (0, 255, 0), and then drew something on it with (100, 255, 0).
(Since it's a 16-bpp image, 255 ix stored as 0xffff and 100 is stored
as 65535 * 100 / 255 == 0x6464 in the file.)
I verified that Edit->Convert to Profile...->sRGB resulted in an
image filled with (0, 255, 0) in that color space (due to gamut
clipping).
Similar to these:
* https://webkit.org/blog-files/color-gamut/Webkit-logo-P3.png
* https://www.dropbox.com/s/tgarynpj65ouafd/insta-logo.png?dl=1
...but in green instead of in red, and hand-drawn by me so no license
concerns.
Some apps seem to generate malformed images that are accepted
by most readers. We now only throw if malformed data would lead to
a write outside the chunky buffer.
When using the BMP encoding, ICO images are expected to contain a 1-bit
mask for transparency. Regardless an alpha channel is already included
in the image, the mask is always required. As stated here[1], the
mask is used to provide shadow around the image.
Unfortunately, it seems that some encoder do not include that second
transparency mask. So let's read that mask only if some data is still
remaining after decoding the image.
The test case has been generated by truncating the 64 last bytes
(originally dedicated to the mask) from the `serenity.ico` file and
changing the declared size of the image in the ICO header. The size
value is stored at the offset 0x0E in the file and I changed the value
from 0x0468 to 0x0428.
[1]: https://devblogs.microsoft.com/oldnewthing/20101021-00/?p=12483
This fixes an issue where GIF images without a global color table would
have the first segment incorrectly interpreted as color table data.
Makes many more screenshots appear on https://virtuallyfun.com/ :^)
TIFF files are made in a way that make them easily extendable and over
the years people have made sure to exploit that. In other words, it's
easy to find images with non-standard tags. Instead of returning an
error for that, let's skip them.
Note that we need to make sure to realign the reading head in the file.
The test case was originally a 10x10 checkerboard image with required
tags, and also the `DocumentName` tag. Then, I modified this tag in a
hexadecimal editor and replaced its id with 30 000 (0x3075 as a LE u16)
and the type with the same value as well. This is AFAIK, never used as
a custom TIFF tag, so this should remain an invalid tag id and type.
