Notes

Three 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.

What is not here yet

Three more are drafted and unpublished: the maths of premultiplied against straight alpha worked through on real type, what 4:2:0 does to a thin red heading, and what an upload form means when it says JPG and then says 100 KB. They go up when they are finished rather than when the list looks tidy.