diff --git a/vllm/multimodal/media/image.py b/vllm/multimodal/media/image.py
index 977a67007..260ebadd4 100644
--- a/vllm/multimodal/media/image.py
+++ b/vllm/multimodal/media/image.py
@@ -8,13 +8,11 @@ import pybase64
 import torch
 from PIL import Image
 
-from vllm.logger import init_logger
+from vllm.utils.serial_utils import tensor2base64
 
 from ..image import convert_image_mode, rgba_to_rgb
 from .base import MediaIO, MediaWithBytes
 
-logger = init_logger(__file__)
-
 
 class ImageMediaIO(MediaIO[Image.Image]):
     def __init__(self, image_mode: str = "RGB", **kwargs) -> None:
@@ -77,17 +75,8 @@ class ImageMediaIO(MediaIO[Image.Image]):
         self,
         media: Image.Image,
         *,
-        image_format: str | None = None,
+        image_format: str = "PNG",
     ) -> str:
-        if image_format is None:
-            logger.warning_once(
-                "The default format of `ImageMediaIO.encode_base64` will be changed "
-                'from "JPEG" to "PNG" in v0.15 to avoid lossy compression. '
-                "To continue using the old default, "
-                'pass `format="JPEG"` explicitly to silence this warning.'
-            )
-            image_format = "JPEG"
-
         image = media
 
         with BytesIO() as buffer:
@@ -121,4 +110,4 @@ class ImageEmbeddingMediaIO(MediaIO[torch.Tensor]):
             return tensor.to_dense()
 
     def encode_base64(self, media: torch.Tensor) -> str:
-        return pybase64.b64encode(media.numpy()).decode("utf-8")
+        return tensor2base64(media)
diff --git a/vllm/multimodal/utils.py b/vllm/multimodal/utils.py
index 2f8c343ca..cd116b9b8 100644
--- a/vllm/multimodal/utils.py
+++ b/vllm/multimodal/utils.py
@@ -11,7 +11,6 @@ import numpy as np
 import numpy.typing as npt
 from PIL import Image
 
-from vllm.logger import init_logger
 from vllm.utils.import_utils import LazyLoader
 
 from .inputs import (
@@ -27,8 +26,6 @@ if TYPE_CHECKING:
 else:
     torch = LazyLoader("torch", globals(), "torch")
 
-logger = init_logger(__name__)
-
 
 def __getattr__(name: str):
     if name == "MEDIA_CONNECTOR_REGISTRY":
@@ -74,7 +71,7 @@ def encode_image_base64(
     image: Image.Image,
     *,
     image_mode: str = "RGB",
-    format: str | None = None,
+    format: str = "PNG",
 ) -> str:
     """
     Encode a pillow image to base64 format.