Nano Banana Placeholders

Nano Banana Placeholders

Use this skill to generate clean, consistent placeholder images while building a website—so layouts look real before final creative is ready.

When to use this skill

• You are building a website/app and need temporary images for:
  • Hero sections (16:9, 21:9)
  • Feature blocks / blog thumbnails (3:2, 4:3)
  • Product cards (1:1, 4:5)
  • Team avatars (1:1)
  • Mobile story/cover assets (9:16)
• You want placeholders that are visually coherent (same palette, lighting, style) across a full UI.
• You want the placeholders to be safe by default: no logos, no brand marks, no recognizable people, no text.

Output standards

• No text in images (placeholders should not contain typography).
• No logos / trademarks / brand lookalikes.
• No recognizable faces (use silhouettes or abstract avatars if needed).
• Prefer simple composition and low distraction (soft gradients, subtle grain, minimal detail).
• Save assets into a predictable folder, e.g. public/placeholders/ or assets/placeholders/.
• Maintain a small JSON manifest for easy wiring in frontend code.

Model selection

Choose the model by intent:

1. Speed / bulk placeholders (default)

• Model: gemini-2.5-flash-image (Nano Banana)
• Use for: most card images, blog thumbnails, generic b-roll

2. Higher-fidelity hero or “marketing-looking” assets

• Model: gemini-3-pro-image-preview (Nano Banana Pro)
• Use for: hero banners, premium landing pages, images that need more controlled composition
• Consider image_size="2K" for hero assets

Aspect ratio mapping (use one of these)

Common web ratios you’ll use:

• Avatar: 1:1
• Blog thumbnail: 3:2 or 4:3
• Product portrait: 4:5 or 3:4
• Phone cover / story: 9:16
• Hero: 16:9 or 21:9

Set it with image_config.aspect_ratio.

Prompting system (repeatable + consistent)

Step 1 — Define the “Placeholder Spec”

For each image, write a short spec:

• id: unique name (e.g., hero-home, card-feature-01)
• ratio: 16:9, 1:1, etc.
• category: hero | card | avatar | product | background
• subject: what it should roughly depict (generic, non-branded)
• style_preset: choose one (below)
• palette: 2–4 colors or a vibe (e.g., “cool neutrals, soft blues”)
• notes: optional composition constraints (e.g., “empty space on left for headline”)

Step 2 — Use a style preset (pick ONE)

A. Abstract Gradient (default, safest)

• “soft abstract gradient, subtle grain, modern, minimal”

B. Minimal 3D Objects

• “simple geometric 3D shapes, matte finish, studio light, no text”

C. Flat Vector Illustration

• “clean vector illustration, minimal details, modern SaaS style, no text”

D. Generic Product Photography

• “unbranded product-like object, neutral background, soft shadow, studio lighting”

Step 3 — Build the final prompt (template)

Use this exact structure to keep outputs consistent:

• What it is + where used
• Ratio + composition requirement
• Style + palette
• Hard constraints (no text/logos/faces)
• Background cleanliness

Prompt template:

"Generate a modern placeholder image for a [CATEGORY] used on a website. Aspect ratio: [RATIO]. Subject: [SUBJECT] (generic, unbranded). Style: [STYLE_PRESET]. Palette: [PALETTE]. Composition: [NOTES]. Constraints: no text, no logos, no trademarks, no recognizable faces, no watermarks besides SynthID. Background: clean, minimal, suitable for UI."

Examples

Hero (16:9) "Generate a modern placeholder image for a hero banner used on a SaaS landing page. Aspect ratio: 16:9. Subject: abstract sense of 'growth' using soft flowing shapes (generic, unbranded). Style: soft abstract gradient, subtle grain, modern, minimal. Palette: cool neutrals with soft blue accents. Composition: leave ~35% clean negative space on the left for headline text overlay. Constraints: no text, no logos, no trademarks, no recognizable faces. Background: clean and minimal."

Avatar (1:1) "Generate a modern placeholder image for a user avatar in a web app. Aspect ratio: 1:1. Subject: abstract profile silhouette icon, friendly and minimal (generic, unbranded). Style: clean vector illustration, minimal details. Palette: neutral gray with a single accent color. Composition: centered. Constraints: no text, no logos, no trademarks, no recognizable faces."

How to use the generation script

Step 1 — Dependencies

Ensure you have the required dependency:

• pip install google-genai

Step 2 — Run the script

Use the provided script in the skill's scripts directory to generate images based on your prompt:

python .agent/skills/frontend-design/scripts/generate_images.py "Your prompt here" "output_filename"

The script uses a built-in API key for convenience, but will respect GEMINI_API_KEY if set in the environment.

Step 3 — Integrate in Frontend

The script will save images in the current directory (or specified path). Move them to your project's public/ or assets/ folder and update your code.

Step 4 — Generate a manifest (Optional)

If generating multiple assets, create a manifest.json in your images folder for easy reference:

{
  "id": "hero-home",
  "ratio": "16:9",
  "file": "/assets/hero-home.png",
  "alt": "Abstract placeholder hero image."
}