Header Redirect after image functions don't work?

I know you cannot header redirect after you output (echo) anything to the browser. But I discovered that I cannot redirect even if I use the normal php image functions, such as:

imagecreatetruecolor
imagejpeg
imagegif
imagepng

These functions are essential for me to call before redirecting (since Im dividing a very large image process into several calls).

Any ideas? Thanks guy!