Batch photo filters

A look is a fixed transform, and a fixed transform lands where the picture already was. Drive the contrast up on a frame exposed a stop down and it stays a stop down — darker and flatter than the frame beside it, with the same tint over the top. That is why a folder run through a filter app comes back looking filtered rather than looking like one shoot, and why a grading suite balances a clip before it grades it.

So the queue reads each photograph first: where its tones sit, how far apart they are, and which way its neutral leans. It takes the median of those readings across the folder, brings every frame to it, and only then applies the look — composed into a single colour table, so it is still one draw through the same shader the rail uses. Each row prints what it measured in that file and the exposure, contrast and warmth move that reading produced. The blind rule is one button away for files that are not a set, and pixel dimensions never change under either.

The files still travel through the queue separately. One is decoded, measured, graded, encoded and released before the next begins, so a folder from a modern camera does not leave forty full-resolution canvases sitting in memory together. The finished files are held until you save them, and that is capped too: once about 600 MB of graded output is waiting (250 MB on an iPhone or iPad), the queue pauses and offers what is done as ZIP part 1, then carries on with the rest.

• JPG to JPG carries camera, lens and exposure data and always removes the location tags; PNG and WebP output carries no capture data at all.
• Levelling reads whole-frame averages and nothing else. It knows where a photograph’s tones sit, not what the photograph is of, so a frame that is mostly one dark coat reads as underexposed and is lifted accordingly — the row says what it measured, and the blind rule is there for that file. For portraits, the optional “Level by faces” gives faces 60% of the weight (it downloads a 0.2 MB face model once); a frame with no face found keeps the plain average.
• A dark interior and a bright exterior can be brought to the same level, but no colour table invents detail that was clipped away in the highlights of one of them.
• WebP is offered only when the browser proves it can encode WebP. Older browsers may refuse that choice instead of silently saving a PNG under the wrong extension.

• Photo filtersFifty-six looks shelved by family, compared four at a time and built into recipes, every thumbnail drawn from the photograph you opened.
• Film looksThe eight emulations on their own, with what each one does to skin written down.
• Black and whiteEight channel and tonal decisions for turning colour into grey.
• Vintage looksFaded-print responses with lifted blacks and colour drift.
• Making a set of photos matchOne look, one strength, a run of pictures, and the judgement calls that sit between them.