image-gen
Backend-agnostic image generation workflow: single images, series with anchor-chain consistency, and batch pipelines. Two backends: Gemini (API) and Nano Banana (local scripts with post-processing).
Reference Loading Table
| Signal | Load These Files | Why |
|---|---|---|
| Every request (always load) | references/series-consistency.md |
Anchor-chain and prompt-file-first rules apply to all generation |
| Every request (always load) | references/backend-selection.md |
Mode decision required before every generation |
Script output gemini |
references/backends/gemini.md |
Gemini API models, env vars, flags |
Script output nano-banana |
references/backends/nano-banana.md |
Nano Banana subcommands, flags, aspect ratios |
Phase 1: Detect Mode and Load References
Run the backend detection script — it reads environment variables and outputs a single word:
python3 skills/content/image-gen/scripts/detect-backend.py
Output values:
gemini— GEMINI_API_KEY or GOOGLE_API_KEY is setask— no key found; ask the user which backend to use
Load references based on output:
- Load
references/series-consistency.md(always — applies to every generation). - Load
references/backend-selection.md(always — needed to pick mode and script). - Load
references/backends/gemini.mdwhen output isgemini. - Ask the user to set
GEMINI_API_KEYor confirm they want to use local scripts when output isask.
Gate: references loaded, backend confirmed before Phase 2.
Phase 2: Write Prompt File
Write the complete prompt to disk before any API call. Prompt files serve as the generation record and the anchor-chain input for series — writing them first means the full intent is on disk before any quota is spent.
File naming:
- Single image:
prompts/YYYY-MM-DD-{slug}.md - Series:
prompts/{series-name}-01.md,prompts/{series-name}-02.md, ...
Prompt file format:
---
model: gemini-3-pro-image-preview
aspect-ratio: 1:1
flags: []
---
Full prompt text here. Be explicit about subject, style, background, and constraints.
Create the prompts/ directory if absent:
mkdir -p prompts
For a series, write all prompt files before calling any generation script. See references/series-consistency.md for the anchor-chain algorithm and why this ordering prevents drift.
Gate: all prompt files written and reviewed before Phase 3.
Phase 3: Select Mode and Script
Use references/backend-selection.md to map the request to the correct script and subcommand.
| Use case | Script | Notes |
|---|---|---|
| Single image, Gemini | scripts/generate_image.py |
--prompt flag |
| Batch from prompt file, Gemini | scripts/generate_image.py |
--batch flag |
| Single or batch with post-processing | scripts/nano-banana-generate.py |
Full flag set in backend ref |
| Series with anchor chain | scripts/nano-banana-generate.py with-reference |
Load ref images from previous outputs |
| Post-processing only | scripts/nano-banana-process.py |
crop, remove-bg, pipeline subcommands |
Gate: script and subcommand identified before Phase 4.
Phase 4: Generate
Call the selected script with absolute paths for output files — relative paths break when scripts run from different working directories.
For series generation, follow the anchor-chain sequence from references/series-consistency.md:
- Generate image 1 with no reference.
- Use output of image 1 as
--referencefor image 2. - Continue: each image references the previous output.
Show the full script output — the user needs status messages, warnings, and partial failure information.
Gate: script exits 0 before Phase 5.
Phase 5: Verify and Report
Visual inspection is mandatory. Read the generated image file to verify:
- Subject matches the prompt
- No unwanted watermarks, logos, or artifacts
- Aspect ratio and framing are correct
- No excessive padding or dark borders that need cropping
If visual inspection fails: regenerate with an adjusted prompt. Report the issue clearly before retrying.
Report to the user:
- Output file path (absolute)
- Image dimensions
- Model used
- Post-processing applied (if any)
- Visual verification result
Report only what was requested. The user did not ask for style suggestions or additional generations.
Error Handling
| Error | Cause | Resolution |
|---|---|---|
GEMINI_API_KEY not set |
Missing env var | export GEMINI_API_KEY=your_key or export GOOGLE_API_KEY=your_key |
No image in response |
Prompt triggered safety filter or text-only response | Adjust prompt phrasing; check for policy-violating content |
Missing dependency: google-genai |
Package not installed | pip install google-genai pillow |
Rate limit exceeded (429) |
Too many API calls | Increase --delay; default 2s may be too aggressive on free tier |
Content policy violation (400) |
Restricted prompt content | Rephrase using neutral language; this restriction is API-side |
No image data in response |
API returned text only | Set response_modalities=["IMAGE", "TEXT"] in config |