Outpainting extension prompt guide
Outpainting grows an image beyond its original edges — turning a portrait into a full scene, or a square into a wide banner. The challenge is consistency: the model only sees the original on one side of the new canvas, so style and perspective can drift fast. This guide builds a prompt and the strategy to keep the extension seamless.
How it works
Good outpainting depends on three things: a prompt that describes the whole continuing scene (not just the original crop), a sensible denoising strength, and prompt mirroring — keeping your style, lighting and quality words identical across every pass while only the content words change. This tool sets the direction context, assembles a continuation prompt, and recommends a denoise band plus an overlap-and-steps strategy for the extension you’re doing.
Why outpainting is harder than inpainting
With inpainting, the model has reference context on all sides of the masked region. Outpainting places the new canvas along one or more outer edges, meaning the model only has context from one direction. It must extrapolate rather than interpolate, which is inherently less constrained and more prone to diverging in perspective, colour temperature, and texture. A prompt that works well for a simple inpaint will often drift noticeably when used for large outpaints.
Denoising strength and why it matters
Denoising strength controls how much the model departs from the masked region. Too high (above 0.9) and the model ignores the overlap entirely, producing a jarring seam. Too low (below 0.5) and it is so constrained by the context pixels that it cannot generate coherent new content. For outpainting, a range roughly between 0.6 and 0.8 tends to work well — enough freedom to create the extension while respecting the edge context. This tool recommends a starting range based on your direction and step size.
Worked example: extending a landscape right
Original image: a mountain lake at golden hour, square crop.
A naive single-pass expansion would extend the canvas by 100% to the right and fill it all at once. Common result: the new sky shade is slightly warmer, the mountains feel lower, and there is a visible brightness seam at the join.
Better approach using this guide:
- Step 1 — extend 30% to the right. Prompt: “golden hour mountain lake, calm reflective water, pine forest to the right, dramatic peaks, warm amber sky, photorealistic, soft light, high detail.” Denoise: 0.65.
- Step 2 — move the canvas and extend another 30%. Use the same style words verbatim: “golden hour … photorealistic, soft light, high detail.” Only change the content description to match what the new area should show.
- Step 3 — repeat for a final extension. Each pass uses the growing edge as context and the mirrored style tokens prevent temperature drift.
Tips and notes
- Extend in steps. Add a quarter or third of canvas at a time. One giant expansion is where drift and repetition come from.
- Keep an overlap. Most tools let you overlap the new region with the original by a strip of pixels — that shared context is what makes the seam vanish.
- Mirror your style words every pass. Identical lighting/style/quality tokens each time anchor the look so it doesn’t wander.
- Describe the scene, not the crop. Tell the model what logically continues off-frame — more sky above, more floor below, the rest of the room to the side.
- Scale down your starting image if doing aggressive expansion. Working at a manageable resolution per pass prevents vram issues and lets you do more refinement steps.
- Upscale at the end, not the beginning. Outpainting at high resolution is slower and more prone to repetition artifacts. Generate at a moderate size, outpaint to the full canvas, then upscale the finished composite.