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codex/codex-rs/ext/image-generation/imagegen_description.md
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alicec-oai 40eac3ce8a Add explicit background control to image generation (#47484)
## What changed

Add the boolean `transparent_background` argument to `image_gen.imagegen` for generation and editing. Map `true` to `transparent` and `false` or omission to `opaque`, replacing the previous `auto` background setting.

Update tool guidance to request transparency for background removal and cutouts, and to preserve existing transparency during edits unless the user asks to change it.

## Testing

Add integration coverage for transparent, opaque, and omitted background arguments across generation, editing, and code-mode generation. Verify that `null`, string, and numeric values return a validation error without dispatching an image request.

GitOrigin-RevId: b10ac200a619c72cc1787da41b49d65d0cde05dd
2026-09-23 07:15:30 +00:00

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Markdown

The `image_gen.imagegen` tool enables image generation from descriptions and editing of existing images based on specific instructions. Use it when:
- The user requests an image based on a scene description, such as a diagram, portrait, comic, meme, or any other visual.
- The user wants to modify an attached or previously generated image with specific changes, including adding or removing elements, altering colors, improving quality/resolution, or transforming the style (e.g., cartoon, oil painting).
Guidelines:
- imagegen needs a few minutes to finish. In code-mode, use the first-line @exec directive to give the initial call 120 seconds and the same yield for any waits that follow. Once it finishes, return the image with generatedImage(result).
- Avoid printing the full result or its base64 image data with `text()` or `notify()`; print only small metadata when needed.
- Set `transparent_background` to true when the request calls for a transparent background, including background removal or a cutout; set it to false otherwise. For edits, preserve existing transparency unless the user asks to change it.
- Omit both `referenced_image_paths` and `num_last_images_to_include` when generating a brand new image.
- For edits, use `referenced_image_paths` when every target image has a local file path.
- If you have not seen a local image yet, use `view_image` to inspect it before editing.
- Use `num_last_images_to_include` only when at least one target image has no local file path.
- Set `num_last_images_to_include` to the smallest number of recent conversation images that includes every target image, up to 5.
- Never provide both `referenced_image_paths` and `num_last_images_to_include`.
- If neither mechanism can include every target image, ask the user to attach the missing images again.
- Directly generate the image without reconfirmation or clarification unless required images must be attached again.
- Always use this tool for image editing unless the user explicitly requests otherwise. Do not use the `python` tool for image editing unless specifically instructed.