Image Generation

Image Generation Skill

Generate or edit images for the current project (website assets, game assets, UI and product mockups, wireframes, logos, photorealistic images, infographics) using onyx-cli image. Generation runs server-side with whatever provider the admin configured at /admin/configuration/image-generation (OpenAI, Gemini, or Azure) — no API key is needed here.

When a provider isn't configured

If onyx-cli image … exits with "no image generation provider is configured", stop and tell the user: image generation is unavailable until an admin configures a provider at /admin/configuration/image-generation. Do not try to work around it with another tool.

When to use

• Generate a new image (concept art, product shot, hero, texture, sprite).
• Generate a new image guided by reference images (style, composition, mood).
• Edit an existing image (background replacement, object removal, lighting/weather change, compositing, inpainting).
• Produce many assets or variants for one task.

When not to use

• Extending or matching an existing SVG/vector icon set, logo system, or illustration library already in the repo — edit those directly.
• Simple shapes, diagrams, wireframes, or icons better produced as SVG / HTML/CSS / canvas.
• A small project-local asset edit when the source already exists in an editable native format.
• Any task where the user clearly wants deterministic code-native output, not a generated bitmap.

Decision tree

1. Intent — new image or edit of an existing image?
   • Modify an existing image while preserving parts of it → image edit.
   • Images supplied only as references for style/composition/mood, or no images → image generate.
2. Execution — one asset or many?
   • One asset → a single command.
   • Many distinct assets → one command per asset (do not use -n for distinct assets; -n produces variants of one prompt).

Assume the user wants a new image unless they clearly ask to change an existing one.

Usage

Generate (text-to-image)

onyx-cli image generate \
  -p "A minimal hero of a ceramic coffee mug, clean product photography, soft studio lighting, wide composition with negative space, no text, no watermark" \
  --shape landscape \
  -o assets/hero.png

Edit / composite existing image(s)

-i/--input-image may be repeated to composite multiple inputs; the first is the primary edit source.

onyx-cli image edit \
  -i assets/product.png \
  -p "Replace only the background with a warm sunset gradient; keep the product and its edges unchanged" \
  -o assets/product-sunset.png

Reference images are sent inline, and the sandbox egress proxy rejects any request body over ~32 MiB with a "request body is larger than the limit" (body_too_large) error. base64 inflates size by ~33%, so keep each -i image roughly under ~20 MB on disk (downscale large source images first). This only affects edit; plain generate has a tiny request body.

Variants of one prompt

onyx-cli image generate -p "Abstract colorful album cover art" -n 3 -o art.png

-n > 1 requires a model that supports multiple images per request (e.g. gpt-image-*). Some models (e.g. dall-e-3) only support -n 1 and will error otherwise; if -n > 1 fails, retry with -n 1.

The command prints the saved file path(s), one per line (multiples get a _N suffix). Open the output with view_image to inspect it and iterate with a single targeted prompt change.

Flags

Workflow

1. Decide intent (generate vs edit) and execution (single vs repeated commands).
2. Collect inputs up front: prompt(s), exact in-image text (verbatim), constraints/avoid list, and any input images with their roles.
3. Shape the prompt by specificity: if it's already detailed, normalize it; if generic, add tasteful detail only when it materially improves the result.
4. Run onyx-cli image …, saving project-bound assets into the workspace. Don't overwrite an existing asset unless asked — use a sibling version (e.g. hero-v2.png).
5. view_image the output; inspect subject, style, composition, and text accuracy; iterate with one targeted change.
6. Report the saved path(s) and the final prompt(s).

Prompt schema

Use these labeled lines as scaffolding; include only the ones that help.

Use case: <photorealistic | product-mockup | ui-mockup | infographic | logo | illustration | concept-art | edit:object | edit:background | edit:style | compositing>
Asset type: <where the asset will be used>
Primary request: <main prompt>
Subject: <main subject>
Style/medium: <photo / illustration / 3D / etc.>
Composition/framing: <wide / close / top-down; placement>
Lighting/mood: <lighting + mood>
Color palette: <palette notes>
Text (verbatim): "<exact text>"
Constraints: <must keep / must avoid>

Prompting best practices

• Structure as scene/backdrop → subject → details → constraints.
• State the intended use (ad, UI mock, infographic) to set polish level.
• Use camera/composition language for photorealism.
• Quote exact in-image text verbatim and specify typography + placement; for tricky words, spell them out and require verbatim rendering.
• For edits, repeat the invariants every iteration (change only X; keep Y unchanged).
• For multi-image inputs, reference each image and describe how to use it.
• Iterate with single-change follow-ups.
• If the prompt is generic, add only detail that materially helps; if it is already detailed, normalize rather than expand.

Source: onyx-dot-app/onyx-foss — distributed by TomeVault.