creating .raw

.raw is just raw data. PSP can create them. The filetype contains exactly what the extension says, raw data. Just dump your data into a file, and you have a .raw file.

If what you want is a real simple image format, you can look into PPM

You can use photoshop to edit/create these. Here is an example of how they are used:

http://www.simoneschbach.com/Data/SkullbonezCore/SkullbonezCoreSource.zip

A .raw file just has the raw pixel data, it doesn't contain the dimensions, the number of colors (or bits per pixel), or anything else. If you have a chunk of pixel data, just dump it into a file, add the .raw extension and you have a .raw file. If you want to create your own format, I think the simpliest setup is creating a header that has the width, height, and the bits per pixel. After that header you could dump in the pixel data just as it occurs in RAM. So your file would have 3, 32-bit unsigned ints, followed by a stream of unsigned 8-bit bytes. You don't need to include the size because width*height*bits_per_pixel/8 = number of bytes of pixel data.

with terragen ,you can create a landscape and export it as a raw heightmap