Understanding IDAT chunk of PNG file format
- by DRapp
From the sample image below, I have a border in yellow just for display purposes only.
The actual .png file is a simple black/white image 3 pixels by 3 pixels. I was originally thinking to try as a 2x2, but that would not help trying to interpret low/hi vs hi/low drawing stream. At least this way, I would have two black, one white from the top, or one white, two black from the bottom..
So I read the chunks of data, get to the IDAT chunk, decode that (zlib) and come up with 12 bytes as follows
00 20 00 40 00 80
So, my question, how does the above get broken down into the 3x3 black and white sample... Also, it is saved in palette format and properly recognizes the bit depth of 1 and color palette of 2... color pallet[0] is RGBA all zeros. Palette1 has RGBA of 255, 255, 255, 0
I'll eventually get into the multiple other depth formats later, just wanted to start with what would expect to be the easiest.
Part II. Any guidance on handling the other depth formats would help if anything special to be considered especially regarding alpha channel (which I am already looking for in the palette) that might trip me up.
