gcbenison gcbenison - 3 months ago 24
Linux Question

Insert a text chunk into a png image

I'm looking for a simple command-line tool (on Linux) to insert a text chunk (e.g. copyright) into a png file, resulting in a new png file:

> png-insert-text-chunk "here's my text chunk" < in.png > out.png


Note: by "insert a text chunk", I do not mean "draw some text on the image". I mean: insert the text into the png file as a chunk, in the technical sense. This can be used, for example, to insert a copyright message that isn't displayed on the actual image.

Answer

I have searched around for utilities to do this, and not yet found anything that really matches what I want to do. So I decided to build my own, which it turns out is not too hard. The utility png-text-dump displays all text chunks in a PNG image. It depends only on libpng. The utility png-text-append inserts text chunks into a PNG image. It depends only on the standard C library - I had initially tried to implement this using libpng, but actually found it easier to work from scratch using only the PNG specification.

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