Notes

Seven pieces, each written against a question people actually type. None of them is a summary of the converter and none of them needs you to use it.

What is here

• Why a PNG turns blackWhat a default black matte is, which tools use one, and the fix.
• Choosing a matte colourWhite, the page colour, a sampled edge, or a value you type.
• When to keep the PNGThe cases where the JPG is bigger, softer, or loses something needed.
• PNG vs JPGThe two formats measured on four drawn test pictures: bytes, edges, transparency.
• The two edge faultsPremultiplied colour and borrowed colour: why one repair darkens and the other lightens.
• Fake transparent PNGsWhy a "transparent" download shows grey squares, and how to tell before converting.
• Form photo and signature sizesThe KB, pixel and DPI rules this site's presets use, each with its source and date.

What is not here yet

Three more are drafted and unpublished: what quality 86 and 4:2:0 actually do to a thin red heading, read from real files; the built-in ways to convert on a phone or a computer without any website; and a dated record of what each browser's canvas encoder writes at each quality. They go up when they are finished rather than when the list looks tidy.