zenmux-image-generation

Imported from zenmux/skills (skills/zenmux-image-generation/SKILL.md). Install upstream with npx skills add zenmux/skills --skill zenmux-image-generation. Copyright stays with the author.

zenmux-image-generation

Turn the user's visual intent into an optimized prompt, confirm the prompt and parameters, then generate or edit images through ZenMux and report the saved files.

Load the current project's config before choosing a model, optimizing a prompt, or refreshing sources. The bundled config.json.example contains portable factory defaults; user preferences live only in the project's runtime directory.

All runtime files belong to the current project under .context/zenmux-image-generation/:

.context/zenmux-image-generation/
  .gitignore    # Ignores generated files; allows .gitignore and config.json in Git
  config.json   # User settings, copied from config.json.example only if absent
  refresh-state.json # Per-resource refresh attempts and successful updates
  output/       # Generated images
  prompts/      # Optimized prompts and generation parameters
  assets/       # Reference images copied/downloaded for this task, if needed
  references/   # Refreshed documentation, cookbooks, and model cache

The helpers resolve the Git root from the original invocation directory (INIT_CWD for npm --prefix); outside Git they use that invocation directory. Run commands from the user's project. The skill may be installed elsewhere; substitute its absolute path in script and --prefix arguments when needed. Existing user reference images can stay in place. Skill code, locked dependencies, and bundled offline references stay in the skill directory.

Initialize the workspace before writing any prompts or downloading assets:

node skills/zenmux-image-generation/scripts/workspace.mjs

This prints the absolute runtime directory, creates its subdirectories and .gitignore, and copies config.json.example to config.json only if missing. Existing user settings and ignore rules are preserved. Both reference refresh and generation also initialize it automatically. Resolve prompt/cache paths from this printed root when invoking from a project subdirectory.

config.json can be committed with the project. Generated images, prompt files, reference caches, and refresh-state.json remain ignored.

Configuration and prompt modes

Read effective settings (missing fields inherit the example without rewriting user settings):

node skills/zenmux-image-generation/scripts/workspace.mjs --config

Precedence: explicit user request/CLI flags > project config > example defaults. Apply one-off requests for a model or prompt mode to this invocation; edit the project config only when the user wants to change their saved preferences. Never write user preferences into the shared example or skill source. Keep API keys in ZENMUX_API_KEY, outside config. Malformed or invalid config reports its path and fails without overwriting the file; fix it instead of silently using defaults.

Set refresh.autoUpdate to false to use local/bundled sources without automatic network requests. Intervals accept non-negative numbers; 0 means refresh on every invocation (failed requests still obey the retry delay). --force bypasses both intervals and autoUpdate for an explicitly requested refresh.

1. Prepare the runtime and refresh sources

Require Node.js 22 or newer; reference commands also need curl and jq. Install locked dependencies once per clone or after dependency changes:

npm ci --prefix skills/zenmux-image-generation

Generation requires ZENMUX_API_KEY. Never accept the key as a CLI argument or print it:

export ZENMUX_API_KEY=...

At the beginning of an invocation, run the refresh check. It downloads only resources whose interval has elapsed, or runs once if there is no refresh history. Fresh caches are reused without network requests. In direct mode, prompt cookbooks are neither copied nor downloaded; API documentation can still refresh:

bash skills/zenmux-image-generation/scripts/refresh_references.sh --quiet
# Only when the user requests an immediate update:
bash skills/zenmux-image-generation/scripts/refresh_references.sh --force
# One-off prompt-mode override, without editing config:
bash skills/zenmux-image-generation/scripts/refresh_references.sh --prompt-mode reference --quiet

Each successfully downloaded reference has its own timestamp in refresh-state.json; unchanged files are skipped even if a different file failed. Failed attempts keep the previous local copy and delay retries. A partial model catalog refresh is not marked fully successful.

If the user named a model, preserve it. Otherwise, list current image models unless the simple default clearly applies:

bash skills/zenmux-image-generation/scripts/list_models.sh
# Machine-readable alternatives:
bash skills/zenmux-image-generation/scripts/list_models.sh --names-only
bash skills/zenmux-image-generation/scripts/list_models.sh --json

The model command uses the same configured cache interval. When due, it merges image models from both https://zenmux.ai/api/v1/models and https://zenmux.ai/api/vertex-ai/v1beta/models, deduplicates exact IDs, and updates the project-local cache. The two catalogs may expose different models. On partial failure it retains additional cached models with a warning. Offline, it falls back to the project cache, then the bundled references/zenmux-image-models.json. --snapshot returns full normalized model records, including output modalities. Use list_models.sh --force for an explicitly requested live lookup or a model-unavailable error. Never invent a model ID from memory.

Read the refreshed files in .context/zenmux-image-generation/references/ first; use same-named bundled references/ files when no cached copy is available. Reference paths below are relative to that selected directory.

Use sources in this order:

1. references/zenmux-openai-image-generation.md for ZenMux OpenAI Images protocol and TypeScript examples.
2. references/zenmux-create-image-edit.md for edit fields, masks, limits, and request shapes.
3. references/openai-typescript-images-generate.md or references/openai-typescript-images-edit.md for the current OpenAI SDK signature.
4. references/zenmux-image-generation.md for the Gemini/Vertex-compatible protocol.
5. references/zenmux-generate-images.md for the complete Vertex AI generateImages / editImage parameter map.
6. references/google-gemini-image-generation.md for Google's latest native Interactions API and the explicit ZenMux compatibility boundary.
7. In reference mode only, the awesome-* files for prompt inspiration, never API truth.

2. Resolve intent

Extract the following. Ask only for missing information that materially changes the result, with at most three focused questions.

Aspect shortcuts:

• Portrait, 竖版, phone wallpaper, story: 1024x1536
• Landscape, 横版, banner, widescreen: 1536x1024
• Square, 方形, logo, icon, social post: 1024x1024
• 4K for gpt-image-2: 3840x2160
• 2K/QHD for gpt-image-2: 2560x1440

Capture every reference path or URL in user-supplied order. Accept local paths, file://, http(s)://, and base64 image data URLs. Number references as [Image #1], [Image #2], and so on in both prompt metadata and prompt text. The flag order must match this numbering.

3. Choose the current model and protocol

The live model catalog is authoritative. The bundled snapshot was refreshed on 2026-09-12 from both endpoints. Useful choices include:

Catalog presence confirms the model ID, not every protocol or parameter. For new models, verify the chosen protocol against current ZenMux documentation. Use preset sizes for gpt-image-2.5-flare until its custom-size limits are explicitly documented; the gpt-image-2 limits below describe that earlier model.

Route by protocol:

• openai/gpt-image-*, bare gpt-image-*, and chatgpt-image-latest use scripts/generate-openai.ts and https://zenmux.ai/api/v1 by default.
• Every other model uses scripts/generate-gemini.ts and https://zenmux.ai/api/vertex-ai.
• If the user explicitly requests Gemini protocol for an OpenAI model, honor it with generate-gemini.ts.

Google’s direct Gemini API now documents client.interactions.create as its native image-generation surface. ZenMux has not documented that route. Through ZenMux, continue using generateContent for Google Gemini image models and generateImages / editImage for all other image models. Do not send an Interactions API payload to ZenMux until ZenMux explicitly announces support. The current @google/genai SDK warns that generateImages is deprecated and will be removed in its next major release no earlier than 2027-01-01. Treat the method as a ZenMux compatibility bridge and re-check ZenMux docs before a major SDK upgrade.

For gpt-image-2, custom WIDTHxHEIGHT values must have both edges divisible by 16, an aspect ratio between 1:3 and 3:1, and 655,360-8,294,400 total pixels. Resolutions above 2560x1440 are experimental; maximum is 3840x2160. Other OpenAI image models should use auto, 1024x1024, 1536x1024, or 1024x1536.

4. Follow OpenAI Create/Edit best practices

Use the Images API for one-shot generation or editing. Use Responses API only when the user's actual product needs conversational, multi-turn image state; the bundled helper intentionally uses Images API.

For generation:

• Call client.images.generate through the TypeScript SDK.
• GPT Image returns b64_json; decode and save the bytes without transcoding.
• Use n for multiple outputs in one request when the model permits it.
• transparent backgrounds require PNG or WebP.
• gpt-image-2 transparent PNG/WebP output is currently a preview capability. Request it with background=transparent; merely asking for PNG does not create an alpha channel.
• output_compression applies only to JPEG or WebP.

For editing:

• Call client.images.edit and convert local/remote/data-URL bytes with the SDK's toFile helper.
• Supply at most 16 input images and preserve their order.
• gpt-image-2 always processes image inputs at high fidelity, so omit input_fidelity. Use input_fidelity=high only for earlier supported GPT Image models when identity preservation matters.
• A mask applies to the first input. It must be PNG, under 4 MB, and match the first image dimensions. Fully transparent mask areas indicate what to edit.
• State the requested change first, then explicitly list everything that must remain invariant.

The scripts accept URL output as a defensive fallback, verify returned image magic bytes, use timeouts/retries, and never overwrite an existing file.

5. Optimize and save the prompt

Resolve the mode from the user's one-off request, otherwise prompt.mode. The calling model performs prompt optimization; this setting is not sent to the image API and does not trigger another paid model call.

• direct (default): optimize from the user's request, provided images, and the calling model's own judgment. Do not search, read, or borrow prompt examples from cookbooks or the web. Skip the cookbook search below. Consult API docs only as needed for valid parameters; those are separate from prompt inspiration.
• reference: use the existing prompt cookbooks to find a few relevant examples, then adapt them to the user's intent. Record the cookbook and entry used in prompt metadata. If no useful example is available, disclose the fallback to direct optimization rather than claiming to have used references.

Both modes accept user-supplied reference images, preserve edit invariants, and use the same confirmation and generation flow. Prompt-reference mode controls example-prompt research only.

In reference mode, search relevant cookbook entries without reading either cookbook end to end:

rg -n '^### No\..*(poster|portrait|product|infographic)' \
  .context/zenmux-image-generation/references/awesome-gpt-image-2.md

Use awesome-gpt-image-2.md for OpenAI-oriented examples and awesome-nano-banana-pro-prompts.md for Gemini-oriented examples. Adapt their structure, not their subject.

Prompt order:

1. Scene/background and composition
2. Main subject and action
3. Materials, lighting, palette, lens/render style
4. Exact quoted copy, when required
5. Edit relationships between [Image #N] inputs
6. Constraints and invariants

For an edit, write surgical instructions such as: "Change only X. Preserve identity, pose, geometry, camera angle, lighting, framing, background, and all unmentioned details." Repeat invariants on every follow-up edit.

Save the prompt as:

.context/zenmux-image-generation/prompts/<YYYYMMDD-HHMMSS>-<short-slug>.md

Use this format, filling in the effective settings for this invocation:

# Optimized prompt — <summary>

- **Prompt mode:** direct
- **Cookbook sources:** none
- **Model:** openai/gpt-image-2.5-flare
- **Size:** 1024x1536
- **Quality:** medium
- **Count:** 4
- **Output format:** png
- **Filename prefix:** launch-poster
- **References:** none
- **Created:** 2026-08-31 14:30 (Asia/Singapore)

---

<optimized prompt body>

Show the optimized prompt and parameters to the user. Do not call the paid generation API until the user confirms. Edit the same prompt file if they ask for small changes.

6. Generate with TypeScript

When config selects an OpenAI image model, generate with its configured defaults (omit flags unless they intentionally override this invocation's settings):

npm --prefix skills/zenmux-image-generation run generate:openai -- \
  --prompt-file ".context/zenmux-image-generation/prompts/<file>.md" \
  --filename-prefix "launch-poster"

OpenAI edit with ordered references and explicit size/quality overrides:

npm --prefix skills/zenmux-image-generation run generate:openai -- \
  --prompt-file ".context/zenmux-image-generation/prompts/<file>.md" \
  --filename-prefix "outfit-edit" \
  --size "1024x1536" --quality "high" \
  --reference-image "/absolute/path/person.png" \
  --reference-image "https://example.com/jacket.webp"

Add --mask-image "/absolute/path/mask.png" for a masked edit. For an earlier GPT Image model, add --input-fidelity high when supported. Add --background transparent --output-format png for a lossless transparent asset, or use WebP plus --compression 85 for a smaller transparent asset.

Gemini/Vertex-compatible model:

npm --prefix skills/zenmux-image-generation run generate:gemini -- \
  --model "google/gemini-3.1-flash-image" \
  --prompt-file ".context/zenmux-image-generation/prompts/<file>.md" \
  --filename-prefix "campaign-poster" \
  --aspect-ratio "2:3" --image-size "1K"

The TypeScript Gemini helper covers both ZenMux protocol shapes:

• Google Gemini image models use generateContent or --stream for generateContentStream. It always requests TEXT and IMAGE, supports up to 14 ordered references, and uses --aspect-ratio / --image-size to build imageConfig.
• Non-Google models use generateImages, or editImage when references are present. Supported CLI mappings include --negative-prompt, --aspect-ratio, --image-size, --seed, --enhance-prompt, --person-generation, --safety-filter-level, --include-rai-reason, --add-watermark, and --guidance-scale.
• --size and --quality are OpenAI passthrough fields when an OpenAI model is deliberately called through Gemini protocol. --image-size becomes sampleImageSize for other generateImages providers where supported.
• ZenMux Vertex protocol does not map GPT Image's background field. Use generate-openai.ts for transparent GPT Image output.
• Provider defaults vary when --aspect-ratio and --image-size are omitted. Some providers may also return a different MIME type than requested; the helper detects PNG/JPEG/WebP magic bytes and saves the matching extension.

--output-dir is optional and defaults to the project's .context/zenmux-image-generation/output/. Relative overrides resolve from the original invocation directory. Pass an override only when the user requests a different location; the automatic ignore rules cover the runtime workspace.

7. Object-storage-safe filenames

Every saved image uses this deterministic shape:

<semantic-prefix>-<model-slug>-<utc-millisecond-timestamp>-<8-hex-run-id>-<index>.<ext>

Example:

launch-poster-openai-gpt-image-2-5-flare-20260912t143012345z-a1b2c3d4-01.png

This is intentionally conservative for Supabase Storage, S3-compatible APIs, CDNs, and signed URLs:

• Lowercase ASCII only in the stem: a-z, 0-9, and -
• One final . before png, jpg, or webp
• No spaces, Unicode, slashes, backslashes, control characters, URL-reserved punctuation, leading dots, or .. segments
• UTC millisecond timestamp for lexical ordering
• Random run ID plus output index to prevent collisions during concurrent runs
• Exclusive file creation so a collision cannot overwrite an existing object

Always pass a concise semantic --filename-prefix. If omitted, the script derives it from the prompt filename and sanitizes it with the same rules.

8. Report and iterate

On success, the scripts print SUCCESS, OUTPUT_DIR, IMAGE_PATHS, and a single-line RESULT_JSON. Parse RESULT_JSON when another tool needs stable machine-readable output. Return clickable absolute paths to the user.

For follow-up edits, preserve the selected image as [Image #1], save a new prompt that restates invariants, confirm it, and run the appropriate edit path.

If generation fails:

• Missing dependency: run npm ci --prefix skills/zenmux-image-generation.
• Model unavailable: rerun list_models.sh --force; use the exact live ID.
• Invalid size: choose the nearest valid dimensions that preserve aspect ratio.
• Reference rejected: convert it to PNG/JPEG/WebP and keep it under the model's input limit.
• Provider rejects multiple outputs: loop calls with --n 1 and retain the same semantic prefix; each run ID keeps filenames unique.