The pages behind the controls
Every control in the lab is a real parameter with a real unit, which makes it honest and leaves it silent. A cell size of eight can tell you it means eight pixels; it cannot tell you why nobody screens at four, or why the number you want changes the moment the file is going to a printer rather than to a phone.
These pages carry that missing half. Between them they cover how the engine keeps the file matching the screen, the one distinction the whole site is built on, the century of printing practice that decided the halftone defaults, the two rival ways of faking a colour you do not have, and three practical questions — removing a filter, official photos, and the sizes the apps want. None needs the others first. Take whichever one matches the thing that is currently puzzling you, and come back for the rest when something else does.
They are written to be read away from the tool, so each one states its own numbers rather than telling you to go and look at a slider.
Looks and rebuilds: two meanings of filter
A single question — did the units the picture is made of change? — sorted into fifteen cases people argue about, including grain, greyscale and duotone.
Read it to know which half of the strip a filter lives in, and why that decides what you can undo.
Why halftone dots have angles
Where 15, 75, 0 and 45 degrees come from, what a rosette actually is, and the arithmetic that decides how many pixels a single dot needs before a printer can hold it.
Read it before sending a screened picture anywhere near paper.
Error diffusion versus ordered dither
Two families that spend missing colours in opposite ways: one carries its mistakes forward and hides them, the other takes a fixed matrix and shows its working.
Read it when a sky has gone stripy and you need to know which knob caused it.
How the lab works
The single engine behind strip, preview, export and batch; the seven steps every render takes in the same order; and what this browser keeps.
Read it when you want to know why the file matches the screen, or what the site stores.
Can a filter be removed from a photo?
Completely, when the original still exists; only approximately, with tone controls, when it does not — and why no tool can do better than that.
Read it before you go looking for a filter remover.
Filters and official photos
The Indian missions' ICAO notice and embassy guidance on passport photos, what 'unaltered' rules out, and the one frame in the lab that is safe for a form.
Read it before you upload a filtered photo to any application.
Sizes for Instagram and WhatsApp
1080 × 1080, 1350 and 1920 — which figure Instagram states and which are observed — and the WhatsApp setting that decides whether a photo stays sharp.
Read it when a posted photo looks softer than the one you saved.
Or skip the reading
Nothing here is required to use anything. Open a picture in the lab and every look and effect appears on your own photograph within a second or two, which answers most of what these pages answer, faster and with less arithmetic. The essays are for afterwards, when a result has surprised you and you want to know whether it was the picture or the method.
Rendered on your computer, not on a server.