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image-generation

The image-generation skill enables text-to-image creation and image-to-image editing using the `generate_media` function with `mode="image"`. It automatically selects from available backends (Google Gemini, OpenAI, Grok, OpenRouter) based on API key availability, or allows manual backend specification. Use this skill when generating original images from text prompts, editing existing images through descriptive prompts, performing batch image generation, iterating on designs through multi-turn refinement, or comparing quality across different image generation backends.

View source Repository: MassGen

Install in Claude Code

Copy

git clone --depth 1 https://github.com/massgen/MassGen /tmp/image-generation && cp -r /tmp/image-generation/massgen/skills/image-generation ~/.claude/skills/image-generation

Then start a new Claude Code session; the skill loads automatically.

Definition

SKILL.md

# Image Generation

Generate images using `generate_media` with `mode="image"`. The system auto-selects the best backend based on available API keys.

## Quick Start

```python
# Simple text-to-image (auto-selects backend)
generate_media(prompt="A cat in space", mode="image")

# Specify backend and quality
generate_media(prompt="A logo for a coffee shop", mode="image",
               backend_type="openai", quality="high")

# Batch generation (parallel)
generate_media(prompts=["sunset over ocean", "mountain landscape", "city at night"],
               mode="image", max_concurrent=3)
```

## Backend Comparison

| Backend | Default Model | Strengths | API Key |
|---------|--------------|-----------|---------|
| **Google** (priority 1) | `gemini-3.1-flash-image-preview` (Nano Banana 2) | Fast, flexible sizes, image editing, multi-turn | `GOOGLE_API_KEY` or `GEMINI_API_KEY` |
| **OpenAI** (priority 2) | `gpt-5.4` | High quality, transparent backgrounds, continuation via response ID | `OPENAI_API_KEY` |
| **Grok** (priority 3) | `grok-imagine-image` | 1k resolution, continuation via stored data URI | `XAI_API_KEY` |
| **OpenRouter** (priority 4) | `google/gemini-3.1-flash-image-preview` | Access to multiple models via single API | `OPENROUTER_API_KEY` |

## Key Parameters

| Parameter | Description | Example |
|-----------|-------------|---------|
| `prompt` | Text description of the image | `"A watercolor painting of mountains"` |
| `backend_type` | Force a specific backend | `"google"`, `"openai"`, `"grok"`, `"openrouter"` |
| `model` | Override default model | `"gemini-3-pro-image-preview"` for studio quality |
| `quality` | Image quality (OpenAI) | `"low"`, `"medium"`, `"high"`, `"auto"` |
| `size` | Image dimensions | See backends reference |
| `aspect_ratio` | Aspect ratio | `"16:9"`, `"1:1"`, `"4:5"` |
| `input_images` | Source images for image-to-image editing | `["photo.jpg"]` |
| `continue_from` | Continuation ID for multi-turn editing | `result["continuation_id"]` |

## Image-to-Image Editing

Transform existing images by providing `input_images`:

```python
generate_media(
    prompt="Make it look like a watercolor painting",
    mode="image",
    input_images=["photo.jpg"]
)
```

Supported backends for image-to-image: Google (Gemini), OpenAI, Grok. The system auto-selects if your current backend doesn't support it.

## Multi-Turn Editing (Continuation)

Iteratively refine images using `continue_from`:

```python
# First generation
result = generate_media(prompt="A logo for a coffee shop", mode="image")

# Refine using the continuation ID
result2 = generate_media(
    prompt="Make the text larger and add a cup icon",
    mode="image",
    continue_from=result["continuation_id"]
)
```

Each backend uses a different continuation mechanism:
- **OpenAI**: Passes `previous_response_id` (stateless)
- **Google Gemini**: In-memory chat store (LRU, 50 items)
- **Grok**: In-memory data URI store (LRU, 50 items)

Continuation only works for single image generation (not batch).

## Google: Gemini vs Imagen

Google supports two API paths. **Gemini (Nano Banana 2) is the default and recommended for most use cases.** Imagen is only needed for advanced reference-image editing features.

- **Gemini models** (`gemini-*`): `generate_content()` — text-to-image, image editing via `input_images`, multi-turn continuation
- **Imagen models** (`imagen-*`): `generate_images()` / `edit_image()` — text-to-image with `negative_prompt`/`seed`/`guidance_scale`, plus style transfer, control editing, and subject consistency via reference images

For studio-quality precision and text rendering, use: `model="gemini-3-pro-image-preview"` (Pro-tier).

## Need More Control?

- **Per-backend sizes, quality options, and quirks**: See [references/backends.md](references/backends.md)
- **Complete `extra_params` reference**: See [references/extra_params.md](references/extra_params.md)
- **Advanced editing (inpainting, style transfer, control, subject)**: See [references/editing.md](references/editing.md)