Choose Canvas > Resize Canvas Option+Command+C to change the canvas size without touching the pixels. Pick which edge or corner the existing artwork clings to with the nine-point anchor grid Command+1 through Command+9, laid out like a number pad.
Tip The width and height fields accept arithmetic—type 32*4 or 320/2 and Dottie does the maths.
Canvas dimensions are capped by the maximum canvas size chosen in Settings > Experimental (1024 per side by default, up to 4096) — in this dialog and everywhere else a size can be set.
Choose Canvas > Resize Image Option+Command+I to rescale all layers to a new size. Scaling is nearest-neighbour, so pixels stay crisp and no new colours are introduced.
Choose Canvas > Split into Tiles to cut the canvas into a grid of equal tiles—one layer per cell—and switch to tileset mode. Dottie suggests a tile size that divides the canvas evenly.
Canvas > Merge Tiles into Canvas does the reverse: it lays the tiles back into their grid, flattens them into a single layer, and leaves tileset mode. If the tileset came from Split into Tiles, the merge crops back to the original canvas size so the two round-trip cleanly.
Some classic systems had non-square pixels. Choose Canvas > Pixel Aspect Ratio Option+Command+R to display the canvas with the correct stretch—for example 8:7 for the Famicom and Super Famicom—while you keep drawing in ordinary pixels.
The Canvas menu also works on all layers at once: Flip Canvas Horizontally Shift+H or Vertically Shift+V, Rotate Canvas Left/Right Control+Command+[ / ], and Nudge Canvas Option+Shift+arrows.
Choose Canvas > Add Reference Image… to bring in any image as a non-editable tracing guide. It’s document-level rather than tied to a layer, sits behind your artwork, and is excluded from exports. Show Reference Image / Hide Reference Image toggles it, and Remove Reference Image clears it.