A slider can be labelled. It cannot, in the width of a 300-pixel panel, explain why it is there. Each of these notes began as a question somebody asked after a conversion had already run and could not be taken back: where did the see-through part go, why does this file have a different extension from the one I asked for, why will the phone open it and the desktop refuse.
They are notes, not tutorials. None of them walks you through this page — there is a numbered list on the front of the site for that, and it is five lines long because the job is five lines long. What these do is name the bargain the format is striking on your behalf, so that what is in front of you is a decision rather than a default somebody else picked.
What HEIC is, and the ways out of it
A container borrowed from video, a codec that halves the file, and the licence that keeps most of Windows from reading either. Start here if a folder of holiday photographs will not open on a laptop.
JPG and JPEG are one format
The answer is in the first line and takes four words. The rest is the three-letter filename limit that produced a question people were still asking thirty years after the limit went away.
Transparency has to become a colour
JPEG has nowhere to put an alpha channel, so every transparent pixel is painted before it is encoded. How to choose what it is painted with, and how to tell when the right answer is to keep the PNG.
What a photo's EXIF block contains
The facts a camera writes into a photo, tag by tag, with the location ones singled out. Read it before sharing originals, or when a photo turns sideways after an edit.
JPG quality, measured
Quality 95, 82 and 60 on one of this site's photographs and on a screenshot of it, with the bytes and the PSNR measured and the damage shown at 400%.
Chroma subsampling: 4:2:0 against 4:4:4
The setting that decides whether coloured text survives. 4:2:0 and 4:4:4 measured side by side, and how the Precise encoder's Auto choice decides.
Photo and signature sizes for Indian online forms
The KB range, box and DPI behind every form preset, each with its source and the date it was checked, and the five commonest reasons a portal says no.
What is deliberately not written down here
There is no separate note on getting a photograph under a stated number of kilobytes, because the page that does it explains itself: the Reduce JPG size route runs that measurement loop — encode, weigh, adjust, encode again — on your own file, and the online forms route adds the pixel box and DPI a portal asks for.
And there is nothing here about editing a photograph — lightening it, retouching it, taking something out of it. None of that happens on this domain. The only changes it makes to a picture are the ones a conversion needs and you ask for: fitting it to a pixel box, cleaning a signature photo down to ink on white, or taking the old background out of a cut-out’s edges.
The converter itself is at the front of the site, and the iPhone case has its own page with the codec warmed up in advance.