Pillarbox

Overview

Pillarbox (also pillarboxing) refers to the display of an image with a narrower aspect ratio within a wider frame, resulting in vertical black bars (mattes) on the left and right. The name derives from the shape of classic, pillar-like British post boxes. Pillarbox is the vertical counterpart to letterbox, where the black bars are at the top and bottom. The terms reverse letterboxing or curtain boxing are also commonly used.

The effect allows material to be displayed in its original aspect ratio and without geometric distortion, rather than being stretched horizontally or cropped at the sides (Pan and Scan).

When Pillarbox Occurs

Pillarbox occurs when content with a narrower aspect ratio is shown on a wider playback format. Typical cases:

• Classic 4:3 material (standard TV, older productions) on a 16:9 screen.
• A 16:9 image within a wider cinema frame, such as 2.39:1.
• Portrait-oriented material (e.g., vertically shot smartphone video) on a horizontal display.

When pillarbox and letterbox occur simultaneously (bars on all four sides), it is referred to as windowbox.

Distinction from Letterbox

Use in Production and Broadcast

In post-production and broadcasting, pillarbox is the clean method for bridging format differences without distorting the image. Broadcasters sometimes use designed pillarboxing, where the side areas are filled with station logos or graphics when 4:3 material is broadcast in a 16:9 format. Image format signaling, such as Active Format Description (AFD), can inform the receiving device how to correctly fit the image to avoid unnecessary pillarboxing or stretching.