What XML is
XML marks up data with nested named tags and optional attributes. It is verbose, strict about being well-formed, and can carry a schema that says what shape a document must have.
Enterprise integrations, government data feeds, RSS, SOAP services and older document formats.
What PNG is
A lossless image format. Text and thin lines stay exactly as drawn, which is what a table is made of.
Slides, chat messages, issue trackers, and anywhere a table has to travel as a picture rather than as data.
What changes when you convert XML to PNG
The first repeating element is treated as the rows. Attributes are read alongside child elements and prefixed so they do not collide with a same-named tag. Nesting one level deep becomes dotted column names; deeper structures are kept as text.
The table is drawn from the data onto a canvas rather than captured from the page, so the whole thing comes out however long it is and however much of it is on screen. Column widths are measured from the content, alternating rows are shaded, and the scale is adjustable so a table for a slide or a print layout can be drawn at two or three times the size.
What carries over from XML to PNG
XML records 3 things about a table that PNG has no way to hold.
An empty cell and a missing one are the same thing in PNG, so a null and an empty string in the XML both come out blank and can no longer be told apart.
XML can hold a value that is itself a list or an object. PNG has only flat cells, so nested values are flattened into one cell rather than being spread across columns.
PNG is the end of the line for this data. Reading the table back out of it is a separate and much harder problem than writing it, so keep the XML if you will need the values again.