diff --git a/src/celeste/modalities/images/providers/byteplus/models.py b/src/celeste/modalities/images/providers/byteplus/models.py
index 0d25a7e3..48ce5809 100644
--- a/src/celeste/modalities/images/providers/byteplus/models.py
+++ b/src/celeste/modalities/images/providers/byteplus/models.py
@@ -129,6 +129,7 @@
             ImageParameter.QUALITY: Choice(options=["2K", "3K", "4K"]),
             ImageParameter.REFERENCE_IMAGES: ImagesConstraint(max_count=14),
             ImageParameter.WATERMARK: Bool(),
+            ImageParameter.OUTPUT_FORMAT: Choice(options=["png", "jpeg"]),
         },
     ),
     Model(
@@ -173,6 +174,8 @@
             ImageParameter.QUALITY: Choice(options=["1K", "1.5K", "2K"]),
             ImageParameter.REFERENCE_IMAGES: ImagesConstraint(max_count=10),
             ImageParameter.WATERMARK: Bool(),
+            ImageParameter.OUTPUT_FORMAT: Choice(options=["png", "jpeg"]),
+            ImageParameter.BACKGROUND: Choice(options=["transparent", "opaque"]),
         },
     ),
     Model(
@@ -217,6 +220,8 @@
             ImageParameter.QUALITY: Choice(options=["1K", "1.5K", "2K"]),
             ImageParameter.REFERENCE_IMAGES: ImagesConstraint(max_count=10),
             ImageParameter.WATERMARK: Bool(),
+            ImageParameter.OUTPUT_FORMAT: Choice(options=["png", "jpeg"]),
+            ImageParameter.BACKGROUND: Choice(options=["transparent", "opaque"]),
         },
     ),
 ]
diff --git a/src/celeste/modalities/images/providers/byteplus/parameters.py b/src/celeste/modalities/images/providers/byteplus/parameters.py
index ae979608..662906e7 100644
--- a/src/celeste/modalities/images/providers/byteplus/parameters.py
+++ b/src/celeste/modalities/images/providers/byteplus/parameters.py
@@ -1,9 +1,15 @@
 """BytePlus parameter mappers for images modality."""
 
 from celeste.parameters import ParameterMapper
+from celeste.providers.byteplus.images.parameters import (
+    BackgroundMapper as _BackgroundMapper,
+)
 from celeste.providers.byteplus.images.parameters import (
     ImageMapper as _ImageMapper,
 )
+from celeste.providers.byteplus.images.parameters import (
+    OutputFormatMapper as _OutputFormatMapper,
+)
 from celeste.providers.byteplus.images.parameters import (
     SizeMapper as _SizeMapper,
 )
@@ -33,11 +39,21 @@ class WatermarkMapper(_WatermarkMapper):
     name = ImageParameter.WATERMARK
 
 
+class OutputFormatMapper(_OutputFormatMapper):
+    name = ImageParameter.OUTPUT_FORMAT
+
+
+class BackgroundMapper(_BackgroundMapper):
+    name = ImageParameter.BACKGROUND
+
+
 BYTEPLUS_PARAMETER_MAPPERS: list[ParameterMapper[ImageContent]] = [
     AspectRatioMapper(),
     QualityMapper(),
     ReferenceImagesMapper(),
     WatermarkMapper(),
+    OutputFormatMapper(),
+    BackgroundMapper(),
 ]
 
 __all__ = ["BYTEPLUS_PARAMETER_MAPPERS"]
diff --git a/src/celeste/providers/byteplus/images/parameters.py b/src/celeste/providers/byteplus/images/parameters.py
index a1d8d48c..1c52265f 100644
--- a/src/celeste/providers/byteplus/images/parameters.py
+++ b/src/celeste/providers/byteplus/images/parameters.py
@@ -37,4 +37,22 @@ class WatermarkMapper(FieldMapper[ImageContent]):
     field = "watermark"
 
 
-__all__ = ["ImageMapper", "SizeMapper", "WatermarkMapper"]
+class OutputFormatMapper(FieldMapper[ImageContent]):
+    """Map output_format to BytePlus output_format field."""
+
+    field = "output_format"
+
+
+class BackgroundMapper(FieldMapper[ImageContent]):
+    """Map background to BytePlus background field."""
+
+    field = "background"
+
+
+__all__ = [
+    "BackgroundMapper",
+    "ImageMapper",
+    "OutputFormatMapper",
+    "SizeMapper",
+    "WatermarkMapper",
+]
diff --git a/tests/unit_tests/test_parameter_wire_contracts.py b/tests/unit_tests/test_parameter_wire_contracts.py
index ddc2dbed..3433cc1e 100644
--- a/tests/unit_tests/test_parameter_wire_contracts.py
+++ b/tests/unit_tests/test_parameter_wire_contracts.py
@@ -15,6 +15,7 @@
 from celeste.modalities.audio.providers.openai import parameters as openai_audio
 from celeste.modalities.images.parameters import ImageParameter
 from celeste.modalities.images.providers.bfl import parameters as bfl
+from celeste.modalities.images.providers.byteplus import parameters as byteplus_images
 from celeste.modalities.images.providers.google import parameters as google_images
 from celeste.modalities.images.providers.openai import parameters as openai_images
 from celeste.modalities.images.providers.topazlabs import parameters as topazlabs
@@ -50,6 +51,7 @@
 IMAGES_VERTEX = google_images.GOOGLE_VERTEX_PARAMETER_MAPPERS
 IMAGES_INTERACTIONS = google_images.GOOGLE_INTERACTIONS_PARAMETER_MAPPERS
 IMAGES_OPENAI = openai_images.OPENAI_PARAMETER_MAPPERS
+IMAGES_BYTEPLUS = byteplus_images.BYTEPLUS_PARAMETER_MAPPERS
 AUDIO_GOOGLE = google_audio.GOOGLE_PARAMETER_MAPPERS
 AUDIO_GROQ = groq_audio.GROQ_PARAMETER_MAPPERS
 AUDIO_OPENAI = openai_audio.OPENAI_PARAMETER_MAPPERS
@@ -354,6 +356,8 @@ def _at(data: dict[str, Any], path: tuple[str, ...]) -> Any:  # noqa: ANN401
         ("mask",),
         {"image_url": "data:image/png;base64,ZnJhbWU="},
     ),
+    (IMAGES_BYTEPLUS, IP.OUTPUT_FORMAT, "jpeg", ("output_format",), "jpeg"),
+    (IMAGES_BYTEPLUS, IP.BACKGROUND, "transparent", ("background",), "transparent"),
     (TOPAZ, IP.OUTPUT_WIDTH, 2048, ("output_width",), 2048),
     (TOPAZ, IP.OUTPUT_HEIGHT, 1536, ("output_height",), 1536),
     (TOPAZ, IP.OUTPUT_FORMAT, "jpeg", ("output_format",), "jpeg"),
@@ -581,6 +585,7 @@ def test_scalar_parameters_use_provider_wire_shape(
         GOOGLE_VERTEX,
         IMAGES_VERTEX,
         IMAGES_OPENAI,
+        IMAGES_BYTEPLUS,
         AUDIO_GOOGLE,
         AUDIO_GROQ,
         AUDIO_OPENAI,