NB2 Batch Generation — 2x2 Contact Sheet Grids

Description

Generate 2x2 contact sheet grids for AI media projects using the Nanobanana MCP (mcp__nanobanana__generate_image). Each call produces a single image with 4 panels for hero frame selection.

When to Use

• User asks to generate or regenerate 2x2 grids, variant frames, or scene images
• User says "generate frames", "run NB2 batch", "regen scenes"
• After prompt block edits when new frames are needed

Generation Settings (recommended defaults)

Prompt Rules

• No character names — use descriptors ("the son", "the soldier", "the mother")
• Strip external tag references — MCP-specific tags from other tools are ignored
• Include grid directive — add "2x2 contact sheet grid, four equal panels, thin borders" in the prompt
• Front-load character descriptions in the first 200 chars
• Camera specs — include lens and film stock for cinematic tone

Reference Images

• Pass up to 3 reference images via input_image_path_1/2/3
• Priority order: character turnaround > location > prop
• Source from your references/approved/ directory

Output

• Save to: runs/grids/variants/{ITEM_ID}/
• Use output_path parameter pointing to the variant directory
• Files are auto-named by the MCP tool

Batch Workflow

1. Load prompts

import json
with open("runs/prompts.json") as f:
    prompts = json.load(f)

2. Build manifest

For each item, extract:

• prompt_text (strip references and external tag refs)
• ref_images (up to 3 resolved absolute paths)
• output_dir (e.g., runs/grids/variants/{item_id}/)

3. Generate in parallel batches of 3

Run 3 concurrent mcp__nanobanana__generate_image calls per batch to balance API load. More may hit rate limits.

4. Example MCP call

{
  "prompt": "2x2 contact sheet grid, four equal panels, thin borders, no text. [scene prompt here]",
  "aspect_ratio": "16:9",
  "model_tier": "nb2",
  "resolution": "4k",
  "negative_prompt": "text, watermark, logo, title card, UI elements, split screen borders, white borders",
  "enable_grounding": false,
  "n": 1,
  "input_image_path_1": "/abs/path/to/turnaround.png",
  "input_image_path_2": "/abs/path/to/location.png",
  "output_path": "/abs/path/to/runs/grids/variants/shot-01/"
}

Cost Reference

• Pro tier: ~$0.04 per image
• 27 scenes × 1 image = ~$1.08 per full pass
• 27 scenes × 4 images = ~$4.32 per variant pass

World / Palette Anchoring (example)

Include a palette hint in each prompt for consistent world identity:

Generation Memory

Every batch run should be logged. This lets future sessions know what was generated, what prompts worked, and what scores were achieved.

Log a generation

python3 "${CLAUDE_SKILL_DIR}/scripts/log-generation.py" log \
  --scene shot-06 \
  --prompt "2x2 contact sheet grid..." \
  --model nb2 \
  --refs "references/approved/characters/hero/front.jpg" \
  --output-path "runs/grids/variants/shot-06/" \
  --notes "Round 2 — strengthened character descriptors"

Attach quality scores after verification

python3 "${CLAUDE_SKILL_DIR}/scripts/log-generation.py" add-scores --scene shot-06

Check what was previously generated

python3 "${CLAUDE_SKILL_DIR}/scripts/log-generation.py" history --scene shot-06

Before generating: always read history first

At the start of any batch run, read the generation history for target items. This tells you:

• Which prompts were already tried
• What worked (GOOD verdict) and what did not (FAIL)
• Whether to iterate on the best prompt or try something new

For log format details, see reference/generation-format.md.

Gotchas

• Model tier escalation — nb2 may auto-escalate to pro tier. Changes cost slightly.
• 2x2 grid splitting — the MCP generates a single 4-panel image. Crop with a separate tool if you need individual frames.
• Reference image limit — NB2 MCP accepts max 3 reference images. Priority: character > location > prop.
• Prompt length — NB2 handles long prompts well, but front-load key descriptors in the first 200 chars.
• Output directory — must exist before generation. Create with mkdir -p if needed.
• Parallel batch size — 3 concurrent calls is the safe limit. More may hit rate limits.