[background image] [designspace] Convert JPEG to PNG with Pillow as part of putBackgroundImage()

pyproject.toml

@@ -22,6 +22,7 @@ dependencies = [
     "ufomerge>=1.8.0",
     "unicodedata2>=15.1.0",
     "skia-pathops>=0.8.0.post1",
+    "pillow>=11.0.0",
 ]
 dynamic = ["version"]
 requires-python = ">=3.10"

requirements.txt

@@ -2,6 +2,7 @@ aiohttp==3.11.2
 cattrs==24.1.2
 fonttools[ufo,unicode]==4.55.0
 glyphsLib==6.9.5
+pillow==11.0.0
 pyyaml==6.0.2
 ufomerge==1.8.2
 unicodedata2==15.1.0

src/fontra/backends/designspace.py

@@ -1188,7 +1188,7 @@ async def getBackgroundImage(self, imageIdentifier: str) -> ImageData | None:
 
     async def putBackgroundImage(self, imageIdentifier: str, data: ImageData) -> None:
         if data.type != ImageType.PNG:
-            raise NotImplementedError("convert image to PNG")
+            data = convertImageData(data, ImageType.PNG)
 
         imageInfo = self._imageMapping.reverse.get(imageIdentifier)
         if imageInfo is None:
@@ -2240,3 +2240,21 @@ def mergeKernGroups(
                 mergedGroups[groupName] = gA + [n for n in gB if n not in gASet]
 
     return mergedGroups
+
+
+def convertImageData(data, type):
+    import io
+
+    from PIL import Image
+
+    image = Image.open(io.BytesIO(data.data))
+    if image.mode == "RGBA" and type == ImageType.JPEG:
+        # from https://stackoverflow.com/questions/9166400/convert-rgba-png-to-rgb-with-pil
+        image.load()  # required for image.split()
+        imageJPEG = Image.new("RGB", image.size, (255, 255, 255))
+        imageJPEG.paste(image, mask=image.split()[3])  # 3 is the alpha channel
+        image = imageJPEG
+
+    outFile = io.BytesIO()
+    image.save(outFile, type)
+    return ImageData(type=type, data=outFile.getvalue())

test-py/test_backends_designspace.py

@@ -10,18 +10,20 @@
 
 from fontra.backends import getFileSystemBackend, newFileSystemBackend
 from fontra.backends.copy import copyFont
-from fontra.backends.designspace import DesignspaceBackend, UFOBackend
+from fontra.backends.designspace import DesignspaceBackend, UFOBackend, convertImageData
 from fontra.backends.null import NullBackend
 from fontra.core.classes import (
     Anchor,
     Axes,
+    BackgroundImage,
     CrossAxisMapping,
     FontAxis,
     FontInfo,
     FontSource,
     GlyphAxis,
     GlyphSource,
     Guideline,
+    ImageType,
     Layer,
     LineMetric,
     OpenTypeFeatures,
@@ -431,6 +433,33 @@ async def test_putGlyph_with_backgroundImage_new_font(testFont, tmpdir):
         assert 0, "expected backgroundImage"
 
 
+async def test_putBackgroundImage_JPEG(writableTestFont):
+    glyph = await writableTestFont.getGlyph("C")
+    for layerName, layer in glyph.layers.items():
+        bgImage = layer.glyph.backgroundImage
+        if bgImage is not None:
+            break
+
+    imageDataPNG = await writableTestFont.getBackgroundImage(bgImage.identifier)
+    imageDataJPEG = convertImageData(imageDataPNG, ImageType.JPEG)
+    assert imageDataJPEG.type == ImageType.JPEG
+
+    glyphName = "D"
+    imageIdentifier = str(uuid.uuid4())
+    bgImage = BackgroundImage(identifier=imageIdentifier)
+
+    glyphD = await writableTestFont.getGlyph(glyphName)
+    firstLayerName = list(glyphD.layers.keys())[0]
+    layer = glyphD.layers[firstLayerName]
+    layer.glyph.backgroundImage = bgImage
+
+    await writableTestFont.putGlyph(glyphName, glyphD, [ord("D")])
+    await writableTestFont.putBackgroundImage(imageIdentifier, imageDataJPEG)
+
+    imageRoundtripped = await writableTestFont.getBackgroundImage(imageIdentifier)
+    assert imageRoundtripped.type == ImageType.PNG
+
+
 async def test_putAxes(writableTestFont):
     axes = await writableTestFont.getAxes()
     axes.axes.append(