How can I do image manipulation on a very large BMP?

Question

I am trying to do some manipulation (specifically, conversion to a different type of splitting into tiles) on a set of very large (a few GB) BMP image files.

I'm not sure I understand the BMP file format, but is it necessary to load the entire file into memory? I was unable to find any API that didn't require loading the entire file at some point. ImageMagick wasn't able to do it either.

Java would be the best tool of choice for me, but any other solution including command line tools or desktop software would be acceptable.

Answer 1

Based on this, it should be reasonably apparent that you can use the fact that it's row-packed. You should be able to read part of a row, store it, advance to the same position in the next row and repeat until you have completed a tile of the desired size. Obviously you may be able to do multiple tiles at once if you can store an entire row worth of tiles in memory all at once.

It is not necessary to load more than the header of the file at once. The header format is describe in the linked Wikipedia entry. It's probably worth paying attention to any compression schemes being used - compression is likely to make this task a bit harder (though still not impossible) :)