Creating Sprites

Generate pixel-art game sprites via OpenAI's gpt-image-1.5 model with native transparent background support, then process them into game-ready assets with correct dimensions and proper anchoring.

Reference Files

File	Read When
references/sprite-sizes.md	Choosing target size, generation size, crop mode, or fake pixel math for a sprite type
references/prompt-guide.md	Constructing or refining a generation prompt, choosing style keywords, or writing per-type prompts
references/troubleshooting.md	A generation fails, transparency check fails, style doesn't match, or API returns errors

Prerequisites

• OPENAI_API_KEY — an OpenAI API key
  • The generate script auto-loads from: --api-key flag → OPENAI_API_KEY env var → .env file in current directory
• Python dependencies: openai and Pillow (installed via requirements.txt in the skill's scripts/ directory)

Script Paths

All scripts/ paths in this skill are relative to the skill directory, not the project directory. Resolve them to absolute paths before running. For example, if the skill is installed at ~/.claude/skills/creating-sprites/, then scripts/generate_sprite.py means ~/.claude/skills/creating-sprites/scripts/generate_sprite.py.

Workflow Checklist

- [ ] Phase 0: Verify prerequisites
- [ ] Phase 1: Determine sprite requirements
- [ ] Phase 2: Prepare reference images
- [ ] Phase 3: Construct prompt
- [ ] Phase 4: Generate candidates
- [ ] Phase 5: Validate candidates
- [ ] Phase 6: Process chosen sprite
- [ ] Phase 7: Save and update plan

Phase 0: Verify Prerequisites

Before doing any work, verify the environment is ready. Handle what you can; only ask the user for things you can't resolve yourself.

1. Check API key — check all three sources:

   python -c "
   import os
   from pathlib import Path
   key = os.environ.get('OPENAI_API_KEY', '')
   if not key:
       env = Path('.env')
       if env.exists():
           for line in env.read_text().splitlines():
               if line.strip().startswith('OPENAI_API_KEY'):
                   key = line.partition('=')[2].strip().strip('\"').strip(\"'\")
   print('OK' if key else 'MISSING')
   "
   

   • If MISSING: ask the user to add OPENAI_API_KEY=their-key to a .env file in the project root, or export it as an environment variable
   • Do NOT proceed past this phase without a valid key

2. Install Python dependencies (do this yourself, don't ask the user): pip install -r <skill-dir>/scripts/requirements.txt

Only the API key requires user action. Everything else you should handle yourself.

Phase 1: Determine Sprite Requirements

Identify what to create and look up its parameters.

1. Determine the entity type: item, enemy, decoration, structure, UI icon, player, pet, animal, boss, terrain tile
2. Read references/sprite-sizes.md for common size examples, generation size, and crop mode — use these as a starting point and adjust based on the specific entity
3. Record these values:
   • target_width and target_height (e.g., 32x32)
   • generation_size (1024x1024 default)
   • crop_mode (bottom-anchor, center, or none)
4. Identify the destination path in the project for the final sprite
5. Identify 1-3 existing sprites that could serve as style references

Phase 2: Prepare Reference Images

Existing sprites are tiny and must be upscaled for the AI model to interpret them. Reference images are passed directly to the API via --reference flags for style matching.

For each reference sprite, run:

python scripts/upscale_reference.py --input path/to/sprite.png --output temp/sprite_upscaled.png

The script auto-calculates the best integer multiplier to reach 500-1024px using nearest-neighbor interpolation (preserves pixel crispness).

If no reference sprites exist (first sprite in the project), skip this phase. The prompt alone will define the style.

Phase 3: Construct Prompt

Read references/prompt-guide.md for the base template, style keywords, and per-type examples.

Every prompt must specify:

• Pixel-art style with era/palette keywords (derived from reference analysis in Phase 2)
• Target fake-pixel dimensions ("a 32x32 pixel art sprite")
• Transparent background (gpt-image-1.5 supports this natively)
• ONE sprite only, centered in frame
• No border, no shadow, no text, no grid
• Subject description
• Anchoring: "touching the bottom of the image" for entities, "centered" for items
• "Match the style of the provided reference images" when references are included

Phase 4: Generate and Validate (Max 3 Attempts)

You get at most 3 generation attempts per sprite. Each attempt produces 4 candidates. Never delete candidates from previous attempts — you will pick the best sprite across ALL attempts at the end.

The --name flag sets the base filename. Use a short, descriptive slug for the sprite (e.g. slime, health_potion, oak_tree). Use a versioned suffix to prevent overwrites across attempts: slime_v1, slime_v2, slime_v3.

Attempt 1 — Initial Generation

Generate with the prompt from Phase 3. The script always requests a transparent background natively, whether or not reference images are provided.

python scripts/generate_sprite.py \
  --prompt "A 32x32 pixel art ..." \
  --output-dir ./sprites-wip \
  --reference temp/ref1_upscaled.png \
  --reference temp/ref2_upscaled.png \
  --count 4 \
  --name slime_v1

Outputs: slime_v1_001.png through slime_v1_004.png.

Validate (run on every attempt):

1. Programmatic check — run on each candidate:

   python scripts/check_transparency.py --input ./sprites-wip/slime_v1_001.png
   

   Output format:

   FILE: slime_v1_001.png
   FORMAT: PNG
   ALPHA_CHANNEL: yes
   TRANSPARENT_PIXELS: 45.2%
   CHECKERBOARD_DETECTED: no
   RESULT: PASS
   

   • PASS: At least 10% transparent pixels, no checkerboard pattern
   • FAIL: No alpha channel, 0% transparency, checkerboard detected, or not PNG

2. Visual inspection — use the Read tool to view each passing candidate alongside the reference images from Phase 3. Compare against the references — don't judge in isolation. A sprite can look fine on its own but still miss the intended style, proportions, or details from the references. Check: matches references? Single sprite? Correct orientation? Right proportions? Matches game style?

If any candidate passes both checks → skip to Pick the Best below.

Attempts 2 and 3 — Diagnose Then Fix

Before each retry, diagnose the failure type from previous attempts. The fix depends on the problem:

Background problems (use prompt refinement, then chromakey)

Symptoms: colored background instead of transparency, checkerboard pattern, unwanted scenery (grass, forest, inventory frame, etc.)

• Attempt 2: Strengthen transparency language in prompt: "isolated sprite on transparent background, no checkerboard pattern, actual PNG transparency, no scenery, no environment"
• Attempt 3 (if background problems persist): Switch to chromakey fallback:
  • Pick a safe background color not present in the subject (see references/troubleshooting.md)
  • Add to prompt: "solid flat [COLOR] background, no gradients, no patterns, no shadows"
  • After generation, process with: process_sprite.py remove-bg --chroma-color HEXCODE

Subject problems (use prompt refinement only — NOT chromakey)

Symptoms: wrong proportions, wrong style, multiple sprites, missing details, wrong pose/orientation — but transparency is fine.

• Attempts 2 and 3: Refine the prompt and/or adjust style keywords. See references/troubleshooting.md. Chromakey does not help here — the problem is the subject, not the background. Keep iterating on prompt wording and style descriptions.

Mixed problems (both background and subject issues)

• Prioritize fixing the subject first (prompt refinement), since chromakey can always fix the background later
• If subject looks good by Attempt 2 but background is still wrong, use chromakey for Attempt 3

python scripts/generate_sprite.py \
  --prompt "Refined prompt ..." \
  --output-dir ./sprites-wip \
  --count 4 \
  --name slime_v2   # then slime_v3 for attempt 3

Validate the same way after each attempt.

Pick the Best (across ALL attempts)

After completing your attempts, review all candidates from every attempt — not just the latest batch. A sprite from Attempt 1 may be better than one from Attempt 3.

Use the Read tool to compare the top candidates side-by-side and against the original reference images — select the one that best matches the intended style and details from the references.

If All 3 Attempts Fail

Create a manual creation task in the implementation plan and move on. Don't block progress on one asset. Save the best attempt as a reference for future manual work.

Phase 6: Process Chosen Sprite

Run the full pipeline on the selected candidate:

python scripts/process_sprite.py pipeline \
  --input ./sprites-wip/slime_002.png \
  --output ./sprites/slime.png \
  --target-width 32 --target-height 32 \
  --crop-mode bottom-anchor

If chromakey was used, add --chroma-color HEXCODE --tolerance 45.

Pipeline steps (can also run individually):

1. Remove background (if chromakey): remove-bg --chroma-color HEXCODE
2. Downscale: nearest-neighbor from generation size to target dimensions
3. Crop per crop mode: bottom-anchor trims sides/top; center and none leave canvas as-is

Post-chromakey re-check: The pipeline automatically detects leftover chroma fringe pixels after background removal. If fringe is detected (>5% of edge pixels match the chroma color), it re-runs removal with tolerance +15 and checks again. Watch the pipeline output for DETECTED/CLEAN/WARNING messages.

After the pipeline completes, run check_transparency.py on the output with --chroma-color HEXCODE to verify:

python scripts/check_transparency.py --input OUTPUT.png --chroma-color HEXCODE

If it fails or the visual check shows artifacts, still use the sprite but add a task to the implementation plan noting the sprite needs manual background cleanup by the user.

Read the final sprite alongside the reference images to verify: matches references, correct dimensions, clean transparency, pixel-art preserved, appropriate crop.

Phase 7: Save and Update Plan

1. Move the final sprite to the correct project folder
2. Clean up temporary upscaled references (temp/)
3. Keep all candidates in sprites-wip/ — do NOT delete any, from ANY attempt. The versioned filenames (slime_v1_001.png, slime_v2_003.png, etc.) make it easy to revisit rejected candidates later
4. Update the implementation plan with integration tasks (add to asset registry, create entity config, etc.)

Anti-Patterns

Avoid	Do Instead
Generating without reference images	Always use 1-3 style references when available
Passing tiny 32px sprites as references	Upscale references to 500-1024px with nearest neighbor first
Bilinear/bicubic downscaling	Always nearest-neighbor to preserve pixel crispness
Multiple sprites in one image	ONE sprite per image, 4 separate API calls
Only visual transparency check	Always run check_transparency.py script first
Green chromakey for plant sprites	Pick a chromakey color not present in the subject
Skipping visual validation	Always Read the image to inspect after programmatic checks
Judging sprites without references	Always compare candidates against the original reference images — never evaluate in isolation
Cropping items	Items stay centered in canvas; only crop entities
Giving up after 1 failed generation	Up to 3 attempts; diagnose failure type and apply the right fix each time
Using chromakey for subject problems	Chromakey fixes backgrounds only; for wrong style/proportions, refine the prompt
Deleting candidates from earlier attempts	Keep ALL candidates; pick the best across all attempts at the end
Reusing the same --name across attempts	Use versioned names (slime_v1, slime_v2, slime_v3) to prevent overwrites
Using generic style keywords	Derive style keywords from studying the project's existing sprites

Dependency Note

This skill requires openai and Pillow. Phase 0 handles installation automatically. This is an approved exception to the standard-library-only rule for scripts.