A couple of years ago I made a small command-line program for setting the DPI/PPI of PNG files. I used the System.Drawing.Bitmap class (i.e. GDI+) to set this property, which had the unfortunate side effect of producing relatively bloated files. Given that the chunk specifying this property is only 21 bytes long, I thought I could do better.
SetDPI version 2 searches for the pHYs chunk and updates it directly, or adds it immediately before the first IDAT chunk if it doesn’t already exist. Files produced by this tool will be at most 21 bytes larger than the original (or the same size when the pHYs chunk was already present).
13,478 bytes; SHA-1: 800D83A390F2AD80772D79D7FB45C7EAAB0D4294