gim to png and reconverion

1. gim to png
- gimconv "skin.gim" -o "image.png"

2. convert 8bit alpha png to 32 bit png
- pngout "image,png" "image(32bit).png" /c6 /force

3. modify 32 bit image via photoshop tool

4. convert 32 bit image to 8bit alpha png
- pngnq -s 1 -n 256 "image(32bit).png"

5. reconverion to gim
- gimconv "image(32bit)-nq8.png" --format_style psp --format_endian little --pixel_order faster --image_format index8