refactor(imagetools): omit sRGB color profile from thumbnails

After some experimentation, it turns out that the old imagemagick code
just discarded any embedded color profile from the source image.

After this commit, we attempt to transform the source image from any
embedded color profile to sRGB, but still omit the sRGB color profile
from the resulting thumbnail.

lektor/imagetools.py

@@ -564,7 +564,8 @@ def _convert_color_profile_to_srgb(im: PIL.Image.Image) -> None:
 
     The image is modified **in place**.
 
-    If the original image has no embedded color profile is it set to sRGB.
+    After conversion, any embedded color profile is removed. (The default color
+    space for the web is "sRGB", so we don't need to embed it.)
     """
     # XXX: The old imagemagick code (which ran `convert` with `-strip -colorspace sRGB`)
     # did not attempt any colorspace conversion.  It simply stripped and ignored any
@@ -573,7 +574,6 @@ def _convert_color_profile_to_srgb(im: PIL.Image.Image) -> None:
     #
     # Here we attempt to convert from any embedded colorspace in the source image
     # to sRGB.
-    #
     if "icc_profile" in im.info:
         profile = PIL.ImageCms.getOpenProfile(io.BytesIO(im.info["icc_profile"]))
         profile_name = PIL.ImageCms.getProfileName(profile)
@@ -582,8 +582,7 @@ def _convert_color_profile_to_srgb(im: PIL.Image.Image) -> None:
         # (See https://ninedegreesbelow.com/photography/srgb-profile-comparison.html)
         if profile_name.strip() not in ("sRGB", "sRGB IEC61966-2.1", "sRGB built-in"):
             PIL.ImageCms.profileToProfile(im, profile, SRGB_PROFILE, inPlace=True)
-    else:
-        im.info["icc_profile"] = SRGB_PROFILE_BYTES
+        im.info.pop("icc_profile")
 
 
 def _compute_thumbnail(

tests/test_imagetools.py

@@ -1,6 +1,5 @@
 import io
 import os
-import re
 from pathlib import Path
 from unittest import mock
 
@@ -106,15 +105,14 @@ def test_convert_color_profile_to_srgb():
     _convert_color_profile_to_srgb(im)
     # Top center of image is red after color transform
     assert im.getpixel((im.width // 2, 0)) == approx((255, 0, 0), abs=10)
+    assert "icc_profile" not in im.info
 
 
 @pytest.mark.requirespillow
-def test_convert_color_profile_to_srgb_add_profile():
+def test_convert_color_profile_to_srgb_no_profile():
     im = PIL.Image.new("RGB", (100, 100), "#999")
     _convert_color_profile_to_srgb(im)
-    profile = PIL.ImageCms.getOpenProfile(io.BytesIO(im.info["icc_profile"]))
-    profile_name = PIL.ImageCms.getProfileName(profile)
-    assert re.match(r"sRGB\b", profile_name)
+    assert "icc_profile" not in im.info
 
 
 @pytest.mark.requirespillow