About this instrument

Adding space around a picture looks like a five-minute feature, and as a feature inside a larger editor it usually is. What makes it worth a dedicated instrument is everything the five-minute version leaves out. A width in millimetres needs a resolution before it means anything. A percentage needs a rule about which edge it resolves against. A border added outside the picture and a border drawn inside it produce different files from the same number. A margin that will be framed wants a heavier lower edge for reasons that are optical rather than arbitrary. None of that fits behind a slider marked thin to thick.

The other half of the case is fitting. A great many people arrive at a tool like this one not because they want a frame but because a photograph is the wrong shape for where it is going and something has to give. Padding it out to the right proportion is the one response that leaves the picture alone, and it deserves to be treated as the main job rather than as a side effect of a border feature.

It does not crop, straighten, retouch, upscale or generate. Nothing on this site removes a pixel from a photograph or invents one, which is a narrower promise than most image tools make and a more checkable one. The border is inert colour of a stated width; the photograph passes through the grid it arrived on.

It also does not do pattern. Shaped edges, textures, drawn frames and shadows are a different kind of work needing a different kind of panel, and a rail full of numeric fields is the wrong instrument for choosing a look. The guide on plain and decorative borders sets out where the line falls and where to go for the other side of it.

The page is a static export with no server behind it. Decoding, compositing and encoding all happen in the browser: the full-resolution composite is drawn on a canvas and the encode runs in a worker so the tab stays responsive on a large file. Decode, composite and encode all execute in the page process, so no request made by this site carries your photograph.

The preview is a working copy capped at 2560 pixels on the long edge, with the border computed in the export’s own terms and scaled by a single factor. That is the reason on-screen proportions are the file’s proportions: one scalar cannot change a ratio, so what is approved on the canvas is what lands in the saved file.

It is one of a set of narrow, single-purpose photograph tools built and maintained by the team behind PictureEditor, whose attribution line sits under the wordmark at the foot of every page. Each site in the set owns one operation and hands the neighbouring jobs to whichever site owns those, rather than growing sideways until they are all the same product.

Corrections to the arithmetic, the metadata reading or the copy are the kind of thing this page most wants to hear about. The measurements here are checkable, and a tool that argues in numbers should be held to them.