Next with GIMP, I decomposed the 16k normalmap into R,G,B grayscale layers and subsequently composed a new 16k map, with R->G, G->Alpha, and B, R->black finally. Saved as a PNG file (compression 9) it's ~49.5 MB. The uncompressed PNG is, however 537.7 MB in size!
Next I used my well-proven 'texconvert' tool that I coded long ago, using the DeVIL lib to compress the modified file as a DXT5 which goes quite fast. The NVDXT tools will not work with big size files as you all know. And they are very slow. One needs however really big size to critically evaluate the resulting quality.
The final DXT5 file is 178.9 MB. So relative to the uncompressed PNG, I got a 3.0:1 compression with my DXT5 enconding (why not 4:1?). Due to Mipmaps?
Anyway the result looks quite good and there seem no obvious bugs in Chris' new CVS code of tonight. I'll get back when I have compared it carefully with the corresponding lossless 16k PNG normalmap.
If I wasn't so busy with finishing my CelestialMatters tutorial (at last), I'd quickly code a little additional module ('remapcolors') to be piped after nms or nmstiles from our nmtools package. Then my tiles from my 64k normalmap could be automatically converted to the new compressed DXT5...
Bye Fridger
