fix: Serialize Pillow images losslessly by default

PiperOrigin-RevId: 852690874

Author: google-genai-bot

google/genai/_transformers.py

@@ -285,29 +285,23 @@ def t_caches_model(
     return model
 
 
-def pil_to_blob(img: Any) -> types.Blob:
-  PngImagePlugin: Optional[builtin_types.ModuleType]
-  try:
-    import PIL.PngImagePlugin
-
-    PngImagePlugin = PIL.PngImagePlugin
-  except ImportError:
-    PngImagePlugin = None
-
-  bytesio = io.BytesIO()
+def pil_to_blob(image: Any) -> types.Blob:
+  image_format = 'PNG'
+  save_params: dict[str, Any] = dict()
   if (
-      PngImagePlugin is not None
-      and isinstance(img, PngImagePlugin.PngImageFile)
-      or img.mode == 'RGBA'
+      image.format == 'JPEG'
+      and getattr(image, 'filename', '')
+      and image.mode in ['1', 'L', 'RGB', 'RGBX', 'CMYK']
   ):
-    img.save(bytesio, format='PNG')
-    mime_type = 'image/png'
-  else:
-    img.save(bytesio, format='JPEG')
-    mime_type = 'image/jpeg'
-  bytesio.seek(0)
-  data = bytesio.read()
-  return types.Blob(mime_type=mime_type, data=data)
+    image_format = 'JPEG'
+    save_params.update(quality='keep')
+
+  image_io = io.BytesIO()
+  image.save(image_io, image_format, **save_params)
+  image_bytes = image_io.getvalue()
+  mime_type = f'image/{image_format.lower()}'
+
+  return types.Blob(data=image_bytes, mime_type=mime_type)
 
 
 def t_function_response(

google/genai/tests/transformers/test_blobs.py

@@ -26,14 +26,17 @@
 
 
 def test_blob_dict():
-  blob = t.t_blob({'data': bytes([0, 0, 0, 0, 0, 0]), 'mime_type': 'audio/pcm'}
-  )
+  blob = t.t_blob({
+      'data': bytes([0, 0, 0, 0, 0, 0]),
+      'mime_type': 'audio/pcm',
+  })
   assert blob.data == bytes([0, 0, 0, 0, 0, 0])
   assert blob.mime_type == 'audio/pcm'
 
 
 def test_blob():
-  blob = t.t_blob(types.Blob(data=bytes([0, 0, 0, 0, 0, 0]), mime_type='audio/pcm')
+  blob = t.t_blob(
+      types.Blob(data=bytes([0, 0, 0, 0, 0, 0]), mime_type='audio/pcm')
   )
   assert blob.data == bytes([0, 0, 0, 0, 0, 0])
   assert blob.mime_type == 'audio/pcm'
@@ -50,10 +53,12 @@ def test_image(image_jpeg):
   assert round_trip_image.mode == image_jpeg.mode
   assert round_trip_image.format == image_jpeg.format
 
+
 def test_not_image():
   blob = types.Blob(data=bytes([0, 0, 0, 0, 0, 0]), mime_type='audio/pcm')
   assert blob.as_image() is None
 
+
 def test_part_image(image_jpeg):
   part = t.t_part(image_jpeg)
   assert part.inline_data.data[6:10] == b'JFIF'
@@ -69,3 +74,11 @@ def test_part_image(image_jpeg):
 def test_part_not_image():
   part = t.t_part('hello world')
   assert part.as_image() is None
+
+
+def test_pil_to_blob_with_memory_pil_image():
+  img = PIL.Image.new('RGB', (1, 1), color='red')
+  blob = t.pil_to_blob(img)
+  assert blob.mime_type == 'image/png'
+  assert blob.data and len(blob.data) == 69
+  assert blob.data[0:4] == b'\x89PNG'