Black bars on left and right sides of the frame—occurs when 4:3 content plays on 16:9 displays or vice versa. Opposite of letterboxing.
Pillarboxing describes a phenomenon you see daily on modern displays — black vertical bars to the left and right of the image content. The reason is simple: the aspect ratio of the material doesn't match the screen. A classic example is an old 4:3 television broadcast on a 16:9 monitor. The projector or player displays the image unscaled in its original size, and the remaining areas remain black because they cannot be filled with anything — without distorting the image.
From a historical perspective, it was a necessary evil: before the transition to widescreen standards, 4:3 was the norm. TV archives, old 16mm footage, even early digital cameras delivered this format. Today — where 16:9 is the global standard — pillarbox situations mainly arise with archive material or when artists deliberately use square or ultra-narrow formats (e.g., TikTok vertical content on large screens). In contrast to letterboxing (black bars at the top and bottom for material that is too wide), pillarboxing works vertically — it "lacks" width instead of height.
On set or in the edit, you should actively manage this. First: clarify the aspect ratio early — for which final format are you shooting or arranging? Second: don't just add black bars in the back if it can be avoided. In a professional workflow, I only pillarbox material if the original must be preserved (archive aesthetic, documentary integrity). Otherwise, I upscale with caution or re-edit to take advantage of the modern format. Third: make it clear during delivery which bars are intentional. Authors get angry if they think your DCP is incorrectly cropped.
A practical tip: black bars can also be a creative opportunity — they can focus attention or deliberately build tension if you use them intermittently. Some directors use variable pillarboxing widths as a stylistic device. But that is conscious direction, not a lack of management.