Strength is literally: how much noise gets poured on your image
Before any "AI" happens, img2img runs your image forward into noise — but only partway. Strength 0.3 stops early (your image clearly survives); strength 1.0 goes all the way to static. The right panel is the actual starting point the denoiser will see. Drag the dial and watch the live correlation between your image and that starting point.
The correlation is computed live between the two panels. In real diffusion, "strength 0.6" means "jump to 60% of the way through the noising schedule and denoise from there" — fewer steps, and less of you left.
Draw something — then let the model re-dream it
Top canvas is a pixel sketchpad — draw on it (or load a preset). Then press Run img2img: your sketch gets noised to the chosen strength and denoised step by step in the bottom canvas by a tiny "model" whose taste is bold flat shapes in this site's palette. Watch it clean up your wobbly lines at low strength, and repaint you at high strength.
Honesty label: this denoiser is a conceptual toy (blur + a palette prior), not a trained network. The mechanics of strength — noise dose, denoise from there — are exactly what Stable Diffusion's img2img does; the artwork is not.
Faithfulness vs creativity — put numbers on the dial
Stop eyeballing. For thirteen strengths from 0.05 to 0.95, we run the full pipeline on your current sketch and measure two things from raw pixel distance: faithfulness (how close is the output to your input) and creativity (how far did it move beyond a mere cleanup). Drag the marker; both curves are recomputed whenever you edit the sketch in EP 02.
Faithfulness = 1 − normalized RMSE(output, your input). Creativity = normalized RMSE(output, a strength≈0 cleanup of your input) — i.e. change that can't be explained as tidying. Both are live measurements, not canned numbers.
The two ways to waste a render
Trigger both classic failures on your own sketch. Strength 0.08: the output is your input with trivially rounded corners — measure it: almost no pixels change. Strength 0.95: the "what changed" heat-map lights up everywhere and composition correlation collapses — your drawing had no say. The middle button shows the same metrics at a sane setting.
Seeds only matter as much as strength lets them
Same sketch, same strength, three different random seeds. At low strength the three outputs are near-identical — the noise is a whisper, your image is the anchor. Crank strength up and the seeds take over: three unrelated pictures. The spread between the outputs (average pairwise pixel RMSE) is computed live as you drag.