Image: compress response images

What it does

This transform re-encodes assistant images and typed images in tool results. It also processes image data URLs and image blocks in JSON function-tool arguments. The options match image_compress_input.

In streams, incomplete function argument fragments stay unchanged. The complete terminal arguments use the compressed image. Custom-tool input and unrelated Base64 stay unchanged.

When the selected output format is jpg, images with an alpha channel remain unchanged. The transform preserves their original bytes, media type, and dimensions. This applies even when every pixel is opaque. It overrides max_edge_px and skip_if_smaller in both responses and streams. Formats that support alpha continue to use the configured compression settings.

Reference

Property	Value
Type ID	`image_compress_output`
Phase	`response`
Scopes	Provider, API key

When to use

Image-generation responses are large and clients pay for transfer.
You want a uniform output format, for example WebP, regardless of the upstream format.

Configuration

Option	Type	Required	Default	Description
`output_format`	string	No	`"original"`	`original`, `jpg`, `jpegxl_lossless`, `jpegxl`, `webp_lossless`, `webp`, or `png`.
`max_edge_px`	integer	No	—	Maximum width or height in pixels. Omit to keep the original dimensions.
`jpeg_quality`	integer	No	`80`	Quality 1-100 for JPEG output.
`jpegxl_quality`	integer	No	`90`	Quality 1-99 for lossy JPEG XL output.
`jpegxl_effort`	integer	No	`7`	JPEG XL encoding effort 1-10. Higher values compress more slowly.
`webp_quality`	integer	No	`80`	Quality 1-100 for lossy WebP output.
`skip_if_smaller`	boolean	No	`true`	Keep the original image when compression does not reduce the payload size.

Example rule

{
  "transform": "image_compress_output",
  "enabled": true,
  "phase": "response",
  "models": [
    "*image*"
  ],
  "config": {
    "output_format": "webp",
    "webp_quality": 80
  }
}