Merge pull request #2898 from wiredfool/pr_2790

Add support for sRGB and cHRM chunks, permit sRGB when no iCCP chunk

PIL/PngImagePlugin.py

@@ -387,12 +387,31 @@ def chunk_tRNS(self, pos, length):
         return s
 
     def chunk_gAMA(self, pos, length):
-
         # gamma setting
         s = ImageFile._safe_read(self.fp, length)
         self.im_info["gamma"] = i32(s) / 100000.0
         return s
 
+    def chunk_cHRM(self, pos, length):
+        # chromaticity, 8 unsigned ints, actual value is scaled by 100,000
+        # WP x,y, Red x,y, Green x,y Blue x,y
+
+        s = ImageFile._safe_read(self.fp, length)
+        raw_vals = struct.unpack('>%dI' % (len(s) // 4), s)
+        self.im_info['chromaticity'] = tuple(elt/100000.0 for elt in raw_vals)
+        return s
+
+    def chunk_sRGB(self, pos, length):
+        # srgb rendering intent, 1 byte
+        # 0 perceptual
+        # 1 relative colorimetric
+        # 2 saturation
+        # 3 absolute colorimetric
+
+        s = ImageFile._safe_read(self.fp, length)
+        self.im_info['srgb'] = i8(s)
+        return s
+
     def chunk_pHYs(self, pos, length):
 
         # pixels per unit
@@ -731,7 +750,9 @@ def _save(im, fp, filename, chunk=putchunk):
         name = b"ICC Profile"
         data = name + b"\0\0" + zlib.compress(icc)
         chunk(fp, b"iCCP", data)
-    else:
+
+        # You must either have sRGB or iCCP.
+        # Disallow sRGB chunks when an iCCP-chunk has been emitted.
         chunks.remove(b"sRGB")
 
     info = im.encoderinfo.get("pnginfo")

Tests/test_file_png.py

@@ -49,6 +49,21 @@ def setUp(self):
         if "zip_encoder" not in codecs or "zip_decoder" not in codecs:
             self.skipTest("zip/deflate support not available")
 
+    def get_chunks(self, filename):
+        chunks = []
+        with open(filename, "rb") as fp:
+            fp.read(8)
+            with PngImagePlugin.PngStream(fp) as png:
+                while True:
+                    cid, pos, length = png.read()
+                    chunks.append(cid)
+                    try:
+                        s = png.call(cid, pos, length)
+                    except EOFError:
+                        break
+                    png.crc(cid, s)
+        return chunks
+
     def test_sanity(self):
 
         # internal version number
@@ -501,18 +516,7 @@ def test_chunk_order(self):
         test_file = self.tempfile("temp.png")
         im.convert("P").save(test_file, dpi=(100, 100))
 
-        chunks = []
-        with open(test_file, "rb") as fp:
-            fp.read(8)
-            with PngImagePlugin.PngStream(fp) as png:
-                while True:
-                    cid, pos, length = png.read()
-                    chunks.append(cid)
-                    try:
-                        s = png.call(cid, pos, length)
-                    except EOFError:
-                        break
-                    png.crc(cid, s)
+        chunks = self.get_chunks(test_file)
 
         # https://www.w3.org/TR/PNG/#5ChunkOrdering
         # IHDR - shall be first

docs/handbook/image-file-formats.rst

@@ -408,9 +408,22 @@ PIL identifies, reads, and writes PNG files containing ``1``, ``L``, ``P``,
 The :py:meth:`~PIL.Image.Image.open` method sets the following
 :py:attr:`~PIL.Image.Image.info` properties, when appropriate:
 
+**chromaticity**
+    The chromaticity points, as an 8 tuple of floats. (``White Point
+    X``, ``White Point Y``, ``Red X``, ``Red Y``, ``Green X``, ``Green
+    Y``, ``Blue X``, ``Blue Y``)
+
 **gamma**
     Gamma, given as a floating point number.
 
+**srgb**
+    The sRGB rendering intent as an integer.
+
+      * 0 Perceptual
+      * 1 Relative Colorimetric
+      * 2 Saturation
+      * 3 Absolute Colorimetric
+
 **transparency**
     For ``P`` images: Either the palette index for full transparent pixels,
     or a byte string with alpha values for each palette entry.