Image is corrupted after PIL's tobytes() method

I want to upload an image to a Google Bucket, however I want to reduce the size of the image before uploading. When I don’t call the self._resize_image method the image gets successfully uploaded without any problems. However, when I call the resize method it works until the image.tobytes() method. After the image.tobytes() method is called the image seems to get corrupted. I tried to debug manually and Googling about the tobytes method, but haven’t found anything so far. Do you have an idea what causes the image to get corrupted or is there an alternative to scale the image?

def _resize_image(self, image: bytes, base_with: int = 300) -> bytes:
    stream = BytesIO(image)
    image ="RGBA")
    width_percentage = base_with / float(image.size[0])
    height_size = int(float(image.size[1]) * float(width_percentage))
    image = image.resize((base_with, height_size), Image.ANTIALIAS)
    # if I do here the picture is still displayed correctly.
    return image.tobytes()  # after this line the picture is getting uploaded, but can't be read by Google anymore.

def upload_image_to_bucket(self, image: bytes, bucket_folder: str, compress: bool = True) -> str:
    if compress:
        # if I don't call this method the picture get's uploaded correctly.
        image = self._resize_image(image=image)
    file_name = f"{UUIDService().create_uuid(length=40)}.jpeg"
    bucket =
    blob = bucket.blob(f"{bucket_folder}/{file_name}")
    blob.upload_from_string(data=image, content_type="image/jpeg")
    return file_name

>Solution :

From Pillow’s documentation on tobytes:

This method returns the raw image data from the internal storage. For compressed image data (e.g. PNG, JPEG) use save(), with a BytesIO parameter for in-memory data.

So the tobytes() method returns Pillow’s internal representation of the image, presumably to be restored with frombytes(). If you want to save the image as JPEG, use the save() method as suggested by the documentation:

output = BytesIO(), format="jpeg")
... # do something with `output`

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