Question about image compression/RTC format

[Gambit37]

I'm experimenting with PNGs for walls and trying different formats to get a good quality/size ratio.

Four custom walls sets in my dungeon as 24-bit BMPs makes a file that's 4249Kb (includes other stuff too).

Converted to 8-bit (256 colour) PNGs, this reduces to 2376Kb.

I then ran PNGCRUSH on the PNGs to optimize them, saving around 120Kb on the original 8-bit file sizes.

However, compiling again resulted in a RTC file that was 2375Kb -- only 1Kb saving over the non-optimized PNGs. I would have expected this to be 120Kb smaller.

Is RTC doing something to PNG image data in the background that I'm unaware of? Is it converting them back to some non-optimized version?

[George Gilbert]

The RTC format is compressed using my own compression algorithm. What I imagine is happening is that RTCs compression of the PNGs is about as good as the PNGCRUSH compression so you don't get much saving by you doing it externally first!

[Gambit37]

Of course, I didn't think of it like that! Cool, that saves a step.