image-gen-letterboxlisted

# Image generator letterbox trick Image generation models (Gemini 3 Pro Image, nano-banana, gemini-2.5-flash-image, and other "Banana" family models) only accept a fixed set of **standard aspect ratios**: `1:1`, `16:9`, `9:16`, `4:3`, `3:4`. Passing a non-standard size (e.g. `2560×423` ≈ 6:1 for a YouTube banner, or `768×2048` for a super-tall infographic) causes one of three failure modes: 1. The model silently picks the nearest supported ratio and ignores your intended framing. 2. The model regenerates the scene "creatively" and destroys any composition you tried to preserve. 3. Spatial instructions in the prompt ("top-left corner", "right third") stop working because the model thinks in terms of its own frame. The fix is to **always work inside a standard ratio**: pad the inputs up to the nearest standard ratio, do the generation there, then crop back. ## When to trigger this skill Trigger whenever you are about to call a Gemini image model AND the target output aspect ratio is not in `{1:1, 16:9, 9:16, 4:3, 3:4}`. Do not assume the model will handle anything else — it won't. Common real-world triggers: - YouTube banners (2560×423, ≈ 6:1) - Twitter / X headers (1500×500, 3:1) - LinkedIn banners (1584×396, 4:1) - Ultra-wide cinematic strips - Tall vertical story strips that don't match 9:16 - Any target where `max(w,h) / min(w,h) > 1.78` (beyond 16:9) If the user-requested dimensions map cleanly to a standard ratio (1920×1080, 1024×1024, 1080×1920, etc.), this skill