Outline

Add an inside or outside border to a sprite. Use a separate layer to hide or recolor the contour independently, or paint it into the sprite’s pixels.

Add an outline

Select a visible, unlocked drawing layer. Apply or cancel pending transforms first.
Choose Filter > Outline….
Under Output, choose New layer or Same layer. Same layer applies to the active pixel layer on the current frame and requires a layer without editable paths or linked fills.
Under Appearance, set Thickness (1–64 pixels), Placement (Outside or Inside) and Color. The color field opens the full color chooser and the document palette.
Choose a Shape: Square, Diamond, Horizontal or Vertical.
With New layer selected, choose your layer and frame scope under Targets.
Compare the result using Preview on canvas, then click Apply.

Drag the title bar to move the dialog out of the way of your artwork.

New layer gives each source a separate raster outline layer immediately above it, in the same folder. Source pixels, paths and live fills stay unchanged. The outline is ordinary pixel content: later source edits do not regenerate it. Inside outlines overlay the source. Outside outlines occupy its background. Same layer paints over the source pixels and inherits the active layer’s opacity and blend mode.

Cancel, the title-bar close button or Escape discard the preview. Apply creates one undo step, including when processing multiple frames or layers. Save natively to retain the layers and editable source; image and animation exports include the result. With New layer and Current frame, the new layer has empty cels on the other frames. Playback stops when the dialog opens.

Advanced controls

Directions: toggle any of the eight neighbors to make directional or custom corners. Thickness repeats this neighborhood; Diamond uses four neighbors.
Background: use Transparency, or Exclude color to ignore an exact RGBA background color as well as transparent pixels. Transparent RGB values are ignored.
Alpha cutoff: source pixels with alpha at or below the cutoff count as background. This tests the rendered layer content before layer opacity/blending.
Components: choose the output R, G, B and A components. Unchecked components become zero; disabling A produces no visible outline.
Wrap edges: connect opposite canvas edges on X, Y or both. Without wrapping, pixels outside the canvas count as background.

A selection clips the generated output; the full source silhouette still defines the outline. Its boundary does not introduce an artificial edge. Off-canvas pixels are excluded from the calculation and stay in the source layer. Hidden or locked sources and folder targets are skipped. All editable layers creates a separate outline for each eligible source. New layers use Normal blending at 100% opacity and inherit their parent folder’s appearance.

Apply is unavailable if no directions are selected, the output is transparent or the settings produce no pixels. A thick outline across many layers or frames may exceed processing or memory limits; reduce thickness or process fewer layers/frames. If a limit is exceeded, the document stays unchanged.