What Is the Knockout Option in Advanced Blending?

The Knockout option in advanced blending settings allows a layer to non-destructively "punch through" underlying layers to reveal content beneath them. Instead of permanently erasing pixels or creating complex clipping masks, Knockout uses the shape or transparency of a specific layer to cut a hole through other layers. This guide explains how the Knockout feature functions, the difference between its settings, and practical ways to use it in non-destructive image editing workflows.

How the Knockout Option Works

Found within the Advanced Blending section of the Layer Style dialog box in raster image editors like Adobe Photoshop, Knockout controls layer transparency penetration.

For the Knockout effect to become visible, the active layer's Fill Opacity must typically be reduced (often to 0%). While regular Opacity fades the entire layer including its layer effects, reducing Fill Opacity hides only the fill pixels. Knockout then dictates how far down through the layer stack that transparency cuts. Any layer styles applied to the knockout layer—such as strokes, bevels, or drop shadows—remain visible on top of the cut-out area.

Shallow Knockout vs. Deep Knockout

The Knockout dropdown menu provides three distinct settings:

  • None: The default setting. The layer behaves normally according to its standard opacity and blend modes.
  • Shallow: Punches a hole through underlying layers within the same layer group or clipping mask. The cutout stops at the base layer of that group, preventing underlying layers outside the group from being affected.
  • Deep: Punches through all layers in the document regardless of grouping, stopping only at the locked Background layer. If no flat Background layer exists, it punches straight through to total canvas transparency (the checkerboard pattern).

Practical Applications

  1. Dynamic Cutout Text: You can create text layers with a Fill Opacity of 0% and a Deep Knockout to cut directly to the background image. If you retype or move the text, the cutout automatically updates without having to regenerate a selection mask.
  2. Hollow Shapes with Styles: By applying a stroke or drop shadow to a vector shape set to Knockout, you create a frame that cuts through specific textures or shapes underneath while preserving its border and shadow.
  3. Complex Mockups and UI Design: Using Shallow Knockout within layer groups allows UI designers to cut holes in buttons, cards, or interface containers without exposing the artboard or canvas behind the parent container.