The ImageConfig currently includes fields like output_mime_type and output_compression_quality, but they are not supported in the Gemini API, as noted in the source code:
output_mime_type: Optional[str] = Field(
default=None,
description="""MIME type of the generated image. This field is not
supported in Gemini API.""",
)
output_compression_quality: Optional[int] = Field(
default=None,
description="""Compression quality of the generated image (for
``image/jpeg`` only). This field is not supported in Gemini API.""",
)
See: https://github.com/googleapis/python-genai/blob/main/google/genai/types.py#L5431
Use Case
In production, we generate a large number of images via Gemini API.
Network bandwidth is a major cost factor.
Being able to control output compression would significantly reduce traffic and cost.
Observation
From testing with gemini-3.1-flash-image-preview, the output appears to be JPEG with very high quality (likely close to 100).
Example:
data = part.inline_data.data
mime_type = part.inline_data.mime_type
print(f'output inline_data: mime={mime_type}, bytes={len(data)}, MB={len(data)/1024/1024:.2f}')Result:
output inline_data: mime=image/jpeg, bytes=3667955, MB=3.50
However, re-encoding the same image locally using:
image.save(..., format="JPEG", quality=92)
produces a file of only ~773 KB (~4× smaller) with no noticeable visual degradation.
Actually, the final image I delivered to end user is compressed with jpeg quality 92, and it is clear enough.
Problem
- The API always returns high-quality images
- Developers cannot control compression level
- This leads to:
- Significant network overhead
- Higher proxy / egress cost
- Unnecessary bandwidth usage at scale
Proposal
Support the following fields in ImageConfig:
- output_mime_type (e.g. image/jpeg)
- output_compression_quality (e.g. 80–95)
Even a simple implementation (JPEG-only, best-effort quality) would already be very valuable.
Additional Benefit
Reducing output size could also:
- Improve latency (faster response transfer)
- Reduce server/network load
- Improve scalability of high-throughput applications
The
ImageConfigcurrently includes fields likeoutput_mime_typeandoutput_compression_quality, but they are not supported in the Gemini API, as noted in the source code:See: https://github.com/googleapis/python-genai/blob/main/google/genai/types.py#L5431
Use Case
In production, we generate a large number of images via Gemini API.
Network bandwidth is a major cost factor.
Being able to control output compression would significantly reduce traffic and cost.
Observation
From testing with
gemini-3.1-flash-image-preview, the output appears to be JPEG with very high quality (likely close to 100).Example:
Result:
However, re-encoding the same image locally using:
produces a file of only ~773 KB (~4× smaller) with no noticeable visual degradation.
Actually, the final image I delivered to end user is compressed with jpeg quality 92, and it is clear enough.
Problem
Proposal
Support the following fields in ImageConfig:
Even a simple implementation (JPEG-only, best-effort quality) would already be very valuable.
Additional Benefit
Reducing output size could also: