Keep pnginfo metadata for gallery (#3150)

* Keep pnginfo metadata for gallery

* add test to pil_to_file for keeping image metadata

* Update CHANGELOG.md

* formatting

---------

Co-authored-by: Abubakar Abid <abubakar@huggingface.co>

CHANGELOG.md

@@ -9,6 +9,7 @@ No changes to highlight.
 ## Documentation Changes:
 * Sort components in docs by alphabetic order by [@aliabd](https://github.com/aliabd) in [PR 3152](https://github.com/gradio-app/gradio/pull/3152)
 * Changes to W&B guide by [@scottire](https://github.com/scottire) in  [PR 3153](https://github.com/gradio-app/gradio/pull/3153)
+* Keep pnginfo metadata for gallery by [@wfng92](https://github.com/wfng92) in [PR 3150](https://github.com/gradio-app/gradio/pull/3150)
 
 ## Testing and Infrastructure Changes:
 No changes to highlight.

gradio/processing_utils.py

@@ -128,26 +128,25 @@ def save_array_to_file(image_array, dir=None):
     return file_obj
 
 
+def get_pil_metadata(pil_image):
+    # Copy any text-only metadata
+    metadata = PngImagePlugin.PngInfo()
+    for key, value in pil_image.info.items():
+        if isinstance(key, str) and isinstance(value, str):
+            metadata.add_text(key, value)
+
+    return metadata
+
+
 def save_pil_to_file(pil_image, dir=None):
     file_obj = tempfile.NamedTemporaryFile(delete=False, suffix=".png", dir=dir)
-    pil_image.save(file_obj)
+    pil_image.save(file_obj, pnginfo=get_pil_metadata(pil_image))
     return file_obj
 
 
 def encode_pil_to_base64(pil_image):
     with BytesIO() as output_bytes:
-
-        # Copy any text-only metadata
-        use_metadata = False
-        metadata = PngImagePlugin.PngInfo()
-        for key, value in pil_image.info.items():
-            if isinstance(key, str) and isinstance(value, str):
-                metadata.add_text(key, value)
-                use_metadata = True
-
-        pil_image.save(
-            output_bytes, "PNG", pnginfo=(metadata if use_metadata else None)
-        )
+        pil_image.save(output_bytes, "PNG", pnginfo=get_pil_metadata(pil_image))
         bytes_data = output_bytes.getvalue()
     base64_str = str(base64.b64encode(bytes_data), "utf-8")
     return "data:image/png;base64," + base64_str

test/test_processing_utils.py

@@ -63,6 +63,16 @@ class TestImagePreprocessing:
         output_base64 = processing_utils.encode_pil_to_base64(img)
         assert output_base64 == deepcopy(media_data.ARRAY_TO_BASE64_IMAGE)
 
+    def test_save_pil_to_file_keeps_pnginfo(self):
+        input_img = Image.open("gradio/test_data/test_image.png")
+        input_img = input_img.convert("RGB")
+        input_img.info = {"key1": "value1", "key2": "value2"}
+
+        file_obj = processing_utils.save_pil_to_file(input_img)
+        output_img = Image.open(file_obj)
+
+        assert output_img.info == input_img.info
+
     def test_encode_pil_to_base64_keeps_pnginfo(self):
         input_img = Image.open("gradio/test_data/test_image.png")
         input_img = input_img.convert("RGB")