I was fiddling around with Imagemagick, and converted a .png image to a .bmp format, and opened it in a hex editor. The file started with 42 4D, which is what it's supposed to be. However, when I converted it to a '.plasma' format, it starts off with the file signature for a .png file. What is the .plasma format, and why does the file signature remain the same? And what should be the file signature for a .plasma format? I haven't found anything of much substance on the net, so... Any explanations would be helpful.
The plasma image format is a build-in format in the ImageMagick library. Good documentation about this can be found here: http://www.imagemagick.org/Usage/canvas/#plasma. But you are not writing a .plasma image because that format does not support writing.
$ convert -list format | grep -i plasma
FRACTAL* PLASMA r-- Plasma fractal image
PLASMA* PLASMA r-- Plasma fractal image
When a format does not support writing the original format (png in your case) of the input file will be used. And that is why you end up with a png file.