From 63c9886ed2795bf51f11f72bf28c3f4eb573e35a Mon Sep 17 00:00:00 2001
From: Benjamin Gilbert <bgilbert@backtick.net>
Date: Tue, 24 Oct 2023 23:55:19 -0500
Subject: [PATCH] Allow writing RGB JPEGs
libjpeg automatically converts RGB to YCbCr by default. Add a
keep_colorspace option to disable libjpeg's automatic colorspace conversion
during write.
---
Tests/test_file_jpeg.py | 14 ++++++++++++++
docs/handbook/image-file-formats.rst | 7 +++++++
src/PIL/JpegImagePlugin.py | 1 +
src/encode.c | 5 ++++-
src/libImaging/Jpeg.h | 3 +++
src/libImaging/JpegEncode.c | 11 +++++++++++
6 files changed, 40 insertions(+), 1 deletion(-)
diff --git a/Tests/test_file_jpeg.py b/Tests/test_file_jpeg.py
index ef070b6c5ba..df32a88e1b3 100644
--- a/Tests/test_file_jpeg.py
+++ b/Tests/test_file_jpeg.py
@@ -141,6 +141,16 @@ def test_cmyk(self):
)
assert k > 0.9
+ def test_rgb(self):
+ def getchannels(im):
+ return tuple(v[0] for v in im.layer)
+
+ im = self.roundtrip(hopper())
+ assert getchannels(im) == (1, 2, 3)
+ im = self.roundtrip(hopper(), keep_colorspace=True)
+ assert getchannels(im) == (ord("R"), ord("G"), ord("B"))
+ assert_image_similar(hopper(), im, 12)
+
@pytest.mark.parametrize(
"test_image_path",
[TEST_FILE, "Tests/images/pil_sample_cmyk.jpg"],
@@ -445,6 +455,10 @@ def getsampling(im):
with pytest.raises(TypeError):
self.roundtrip(hopper(), subsampling="1:1:1")
+ # RGB colorspace, no subsampling by default
+ im = self.roundtrip(hopper(), subsampling=3, keep_colorspace=True)
+ assert getsampling(im) == (1, 1, 1, 1, 1, 1)
+
def test_exif(self):
with Image.open("Tests/images/pil_sample_rgb.jpg") as im:
info = im._getexif()
diff --git a/docs/handbook/image-file-formats.rst b/docs/handbook/image-file-formats.rst
index fe310df6443..87275fcdc7c 100644
--- a/docs/handbook/image-file-formats.rst
+++ b/docs/handbook/image-file-formats.rst
@@ -483,6 +483,13 @@ The :py:meth:`~PIL.Image.Image.save` method supports the following options:
**exif**
If present, the image will be stored with the provided raw EXIF data.
+**keep_colorspace**
+ If present and true, indicates that the encoder should retain the
+ image's original color space, rather than automatically converting RGB to
+ YCbCr.
+
+ .. versionadded:: 10.2.0
+
**subsampling**
If present, sets the subsampling for the encoder.
diff --git a/src/PIL/JpegImagePlugin.py b/src/PIL/JpegImagePlugin.py
index 3596e089949..26c9f2da5c7 100644
--- a/src/PIL/JpegImagePlugin.py
+++ b/src/PIL/JpegImagePlugin.py
@@ -783,6 +783,7 @@ def validate_qtables(qtables):
progressive,
info.get("smooth", 0),
optimize,
+ info.get("keep_colorspace", False),
info.get("streamtype", 0),
dpi[0],
dpi[1],
diff --git a/src/encode.c b/src/encode.c
index 4664ad0f32a..596e62bcb51 100644
--- a/src/encode.c
+++ b/src/encode.c
@@ -1042,6 +1042,7 @@ PyImaging_JpegEncoderNew(PyObject *self, PyObject *args) {
Py_ssize_t progressive = 0;
Py_ssize_t smooth = 0;
Py_ssize_t optimize = 0;
+ int keep_colorspace = 0;
Py_ssize_t streamtype = 0; /* 0=interchange, 1=tables only, 2=image only */
Py_ssize_t xdpi = 0, ydpi = 0;
Py_ssize_t subsampling = -1; /* -1=default, 0=none, 1=medium, 2=high */
@@ -1059,13 +1060,14 @@ PyImaging_JpegEncoderNew(PyObject *self, PyObject *args) {
if (!PyArg_ParseTuple(
args,
- "ss|nnnnnnnnnnOz#y#y#",
+ "ss|nnnnpnnnnnnOz#y#y#",
&mode,
&rawmode,
&quality,
&progressive,
&smooth,
&optimize,
+ &keep_colorspace,
&streamtype,
&xdpi,
&ydpi,
@@ -1150,6 +1152,7 @@ PyImaging_JpegEncoderNew(PyObject *self, PyObject *args) {
strncpy(((JPEGENCODERSTATE *)encoder->state.context)->rawmode, rawmode, 8);
+ ((JPEGENCODERSTATE *)encoder->state.context)->keep_colorspace = keep_colorspace;
((JPEGENCODERSTATE *)encoder->state.context)->quality = quality;
((JPEGENCODERSTATE *)encoder->state.context)->qtables = qarrays;
((JPEGENCODERSTATE *)encoder->state.context)->qtablesLen = qtablesLen;
diff --git a/src/libImaging/Jpeg.h b/src/libImaging/Jpeg.h
index 5cc74e69bf5..518e04880e7 100644
--- a/src/libImaging/Jpeg.h
+++ b/src/libImaging/Jpeg.h
@@ -74,6 +74,9 @@ typedef struct {
/* Optimize Huffman tables (slow) */
int optimize;
+ /* Disable automatic colorspace conversion if nonzero */
+ int keep_colorspace;
+
/* Stream type (0=full, 1=tables only, 2=image only) */
int streamtype;
diff --git a/src/libImaging/JpegEncode.c b/src/libImaging/JpegEncode.c
index 9da830b186f..a0b9363852c 100644
--- a/src/libImaging/JpegEncode.c
+++ b/src/libImaging/JpegEncode.c
@@ -137,6 +137,17 @@ ImagingJpegEncode(Imaging im, ImagingCodecState state, UINT8 *buf, int bytes) {
/* Compressor configuration */
jpeg_set_defaults(&context->cinfo);
+ /* Prevent RGB -> YCbCr conversion */
+ if (context->keep_colorspace) {
+ J_COLOR_SPACE space = context->cinfo.in_color_space;
+#ifdef JCS_EXTENSIONS
+ if (context->cinfo.in_color_space == JCS_EXT_RGBX) {
+ space = JCS_RGB;
+ }
+#endif
+ jpeg_set_colorspace(&context->cinfo, space);
+ }
+
/* Use custom quantization tables */
if (context->qtables) {
int i;