What HTML is
An HTML table is a table element containing thead and tbody, with th cells for headers and td cells for data.
Web pages, email templates and anything pasted into a CMS.
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 HTML to PNG
The first table in the markup is used. Cell contents are stripped of inline tags and entities are decoded, so <td><b>Total</b> </td> arrives as Total. Nested tables inside a cell are not descended into.
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 HTML to PNG
HTML records 3 things about a table that PNG has no way to hold.
HTML 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.
Nothing in PNG records that the first row is a header. It is drawn at the top and looks like one, which is all that is left of the distinction.
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 HTML if you will need the values again.