I was in need of a quick conversion from LZW-compressed TIFF to CCITT G4, and PhotoPaint 6 wasn't able to read the file.
So, I downloaded PMView to see if that would work. The image is 12981x888 at 1 bit per pixel. After getting that silly Win2K message about increasing my swap file size, I ended up killing PMView. Later, after things were closed, I ran only PMView, and tracked its memory usage. It began by immediately allocating over 200MB of memory, then fluctuated up and down during the image load (always over 100MB), until the image was finished loading, at which point it sat still at 200MB. Keeping this image in memory requires a whole lot less memory than this - two other editors take up 20-25MB total with the image fully loaded. A bit of simple math shows that the image data itself only adds up to about 13.75MB.