fix(images): forward gpt-image supported params like background to OpenAI and Azure

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

litellm/types/utils.py

@@ -2543,6 +2543,7 @@ class ImageResponse(OpenAIImageResponse, BaseLiteLLMOpenAIResponseObject):
         )
         super().__init__(created=created, data=_data, usage=_usage)
 
+        self.background = kwargs.get("background", None)
         self.quality = kwargs.get("quality", None)
         self.output_format = kwargs.get("output_format", None)
         self.size = kwargs.get("size", None)

litellm/utils.py

@@ -3338,6 +3338,9 @@ def get_optional_params_image_gen(
             continue
         passed_params[k] = v
 
+    provider_supported_params: Final[tuple[str, ...]] = (
+        tuple(provider_config.get_supported_openai_params(model=model or "")) if provider_config is not None else ()
+    )
     default_params: Final = {
         "n": None,
         "quality": None,
@@ -3348,6 +3351,7 @@ def get_optional_params_image_gen(
         "imageConfig": None,
         "tools": None,
         "web_search_options": None,
+        **{k: None for k in provider_supported_params},
     }
 
     non_default_params: Final = _get_non_default_params(
@@ -3407,10 +3411,9 @@ def get_optional_params_image_gen(
         if size is not None:
             optional_params["aspectRatio"] = _map_openai_size_to_vertex_ai_aspect_ratio(size)
 
-    openai_params: list[str] = list(default_params.keys())
-    if provider_config is not None:
-        supported_params = provider_config.get_supported_openai_params(model=model or "")
-        openai_params = list(supported_params)
+    openai_params: Final[list[str]] = (
+        list(provider_supported_params) if provider_config is not None else list(default_params.keys())
+    )
 
     optional_params = add_provider_specific_params_to_optional_params(
         optional_params=optional_params,

tests/test_litellm/test_utils.py

@@ -330,6 +330,37 @@ def test_get_optional_params_image_gen():
     assert optional_params["n"] == 3
 
 
+@pytest.mark.parametrize("custom_llm_provider", ["openai", "azure"])
+def test_get_optional_params_image_gen_keeps_gpt_image_supported_params(custom_llm_provider):
+    """https://github.com/BerriAI/litellm/issues/38649"""
+    from litellm.types.utils import LlmProviders
+
+    provider_config = ProviderConfigManager.get_provider_image_generation_config(
+        model="gpt-image-2", provider=LlmProviders(custom_llm_provider)
+    )
+    optional_params = get_optional_params_image_gen(
+        model="gpt-image-2",
+        n=1,
+        size="1024x1024",
+        custom_llm_provider=custom_llm_provider,
+        provider_config=provider_config,
+        background="transparent",
+        output_format="png",
+        moderation="low",
+        output_compression=50,
+        unknown_param="kept-in-extra-body",
+    )
+    assert optional_params == {
+        "n": 1,
+        "size": "1024x1024",
+        "background": "transparent",
+        "output_format": "png",
+        "moderation": "low",
+        "output_compression": 50,
+        "extra_body": {"unknown_param": "kept-in-extra-body"},
+    }
+
+
 def test_get_optional_params_image_gen_vertex_ai_size():
     """Test that Vertex AI image generation properly handles size parameter and maps it to aspectRatio"""
     # Test with various size parameters

tests/test_litellm/types/test_types_utils.py

@@ -759,3 +759,12 @@ def test_delta_function_tool_call_unchanged_by_custom_support():
     delta = Delta(tool_calls=[{"index": 0, "id": "c2", "type": "function", "function": {"name": "g", "arguments": ""}}])
     assert isinstance(delta.tool_calls[0], ChatCompletionDeltaToolCall)
     assert "custom" not in delta.model_dump()["tool_calls"][0]
+
+
+def test_image_response_keeps_background():
+    """https://github.com/BerriAI/litellm/issues/38649"""
+    from litellm.types.utils import ImageResponse
+
+    response = ImageResponse(created=1, data=[{"b64_json": "aGk="}], background="transparent", output_format="png")
+    assert response.background == "transparent"
+    assert response.model_dump()["background"] == "transparent"