useful image tools

Post about useful image tools in general as the title says.
the usual tools:
Irfanview
xnview
gimp
paintnet

Anyway, I want to talk about a specific issue(s): file size reduction
more specifictly color reduction
I have been quite unhappy ever since windows xp no longer supports 16 bit colors for desktop as well as images. Since then all image manipulation programs also no longer support 16 bit formats (or versions).
Now a day it has become more important since I do mods. I used to use an old DOS program for converting normal PNG 32/24bit to 16 bit. Since I lost it among other things recently I have been looking hard for a replacement. Nada so far. None satisfy my requirement nor can I find the old one again. However, it appears L3DT can save 16 bit images. Far from what I need...

Hmm, i never paid attention to such issue, but ithink i can do everything in photoshop... Actually it's the only programm i need for like everything, except for quick view/manipulation so i don't know many programms that can convert images...

But i'm sure there should be plenty of what you need, it's just finding if and how they perform that certain action is not easy until you try em..

Nah, I don't like Adoby software that much and Photoshop isn't that good only for "photo pictures" not images where you need quality or sharpness or precision; in other word, for anything where it counts. Because of that it's good for making fakes, so you can't determine due to it's bad quality. Photoshop can convert but it has not that good options. The old one I got I could set a percentage of quality based on which the number of colors is reduced. I just can't find any that does that anymore. Being a DOS program I want a small sized one, too.
I found people saying RawTherapee can do it.
I only tested PVRTexTool yet, it does a very good job, but no way to set a level, either.