Sample image format at random, if the format is not selected

src/c++/perf_analyzer/genai-perf/genai_perf/llm_inputs/synthetic_image_generator.py

@@ -28,6 +28,7 @@
 import random
 from enum import Enum, auto
 from pathlib import Path
+from typing import Optional, cast
 
 from genai_perf import utils
 from PIL import Image
@@ -50,9 +51,13 @@ def create_synthetic_image(
         image_width_stddev: int,
         image_height_mean: int,
         image_height_stddev: int,
-        image_format: ImageFormat,
+        image_format: Optional[ImageFormat] = None,
     ) -> str:
         """Generate base64 encoded synthetic image using the source images."""
+        if image_format is None:
+            image_formats = list(ImageFormat)
+        else:
+            image_formats = [cast(ImageFormat, image_format)]
         width = cls._sample_random_positive_integer(
             image_width_mean, image_width_stddev
         )
@@ -63,8 +68,9 @@ def create_synthetic_image(
         image = cls._sample_source_image()
         image = image.resize(size=(width, height))
 
-        img_base64 = utils.encode_image(image, image_format.name)
-        return f"data:image/{image_format.name.lower()};base64,{img_base64}"
+        selected_format = random.choice(image_formats)
+        img_base64 = utils.encode_image(image, selected_format.name)
+        return f"data:image/{selected_format.name.lower()};base64,{img_base64}"
 
     @classmethod
     def _sample_source_image(cls):

src/c++/perf_analyzer/genai-perf/genai_perf/parser.py

@@ -476,9 +476,9 @@ def _add_image_input_args(parser):
         "--image-format",
         type=str,
         choices=utils.get_enum_names(ImageFormat),
-        default="png",
         required=False,
-        help=f"The compression format of the images.",
+        help=f"The compression format of the images. "
+        "If format is not selected, format of generated image is selected at random",
     )
 
 

src/c++/perf_analyzer/genai-perf/tests/test_json_exporter.py

@@ -253,7 +253,7 @@ def test_generate_json(self, monkeypatch) -> None:
           "image_width_stddev": 0,
           "image_height_mean": 100,
           "image_height_stddev": 0,
-          "image_format": "png",
+          "image_format": null,
           "concurrency": 1,
           "measurement_interval": 10000,
           "request_rate": null,

src/c++/perf_analyzer/genai-perf/tests/test_synthetic_image_generator.py

@@ -97,3 +97,24 @@ def test_base64_encoding_with_different_formats(image_format):
     img_bytes = BytesIO(img_data)
     image = Image.open(img_bytes)
     assert image.format == image_format.name
+
+
+def test_null_format_is_accepted():
+    img_base64 = SyntheticImageGenerator.create_synthetic_image(
+        image_width_mean=100,
+        image_width_stddev=100,
+        image_height_mean=100,
+        image_height_stddev=100,
+        image_format=None,
+    )
+
+    # check prefix
+    expected_prefix = "data:image/"
+    assert img_base64.startswith(expected_prefix), "unexpected prefix"
+
+    # check image format
+    data = img_base64.split(",")[1]
+    img_data = base64.b64decode(data)
+    img_bytes = BytesIO(img_data)
+    image = Image.open(img_bytes)
+    assert image.format in [f.name for f in ImageFormat]