Resize so that width is multiple of 4

[zedrummer]

Hello
I use textures for my 3D programming and I would be interested in automatically resize pictures so that they have a width that is a multiple of 4 (as OpenGL only accept that). For example, if the width is a 32bit unsigned integer, performing a bitwise AND 0xFFFFFFFC to get the immediate smaller size multiple of 4. Is there an easy way to do something like that with NConvert? If not, is there an easy way for a program in C calling NConvert to get the size?
Thanks
Cathy L.