If one profile uses PCSXYZ and the other PCSLAB as connection space,
we now do the necessary XYZ/LAB conversion.
With this and the previous commits, we can now convert from profiles
that use PCSLAB with mAB, such as stress.jpeg from
https://littlecms.com/blog/2020/09/09/browser-check/ :
% Build/lagom/icc --name sRGB --reencode-to serenity-sRGB.icc
% Build/lagom/bin/image -o out.png \
--convert-to-color-profile serenity-sRGB.icc \
~/src/jpegfiles/stress.jpeg
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).
This implements conversion from profile connection space to the
device-dependent color for matrix-based profiles.
It only does the inverse color transform but does not yet do the
inverse tone reproduction curve transform -- i.e. it doesn't
implement many cases (LUT transforms), and it does the one thing
it does implement incorrectly. But to vindicate the commit a bit,
it also does the incorrect thing very inefficiently.
This can be used to convert a profile-dependent color to the L*a*b*
color space.
(I'd like to use this to implement the DeltaE (CIE 2000) algorithm,
which is a metric for how similar two colors are perceived.
(And I'd like to use that to evaluate color conversion roundtrip
quality, once I've implemented full conversions.)
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.
The patch also contains modifications on several classes, functions or
files that are related to the `JPGLoader`.
Renaming include:
- JPGLoader{.h, .cpp}
- JPGImageDecoderPlugin
- JPGLoadingContext
- JPG_DEBUG
- decode_jpg
- FuzzJPGLoader.cpp
- Few string literals or texts
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
