While not common, in rare cases you may have an image in its raw pixel format (say in rgb565). It can even be a portion of video. If you ever come accross converting such raw data to say a png or jpeg image, ffmpeg can be used easily. See the following command:
ffmpeg -vcodec rawvideo -f rawvideo -pix_fmt rgb565 -s 1024x768 -i image.raw -f image2 -vcodec png image.png
1024x768 is the geometry. image.raw is the file containing the image in rgb565 format. image.png is the new file to be written.
Need to great a jpeg file? One can use -vcodec mjpeg image.jpg instead of png.
What if image.raw contains data for multiple frames (of a video)? You can use "%d" and ffmpeg will automatically name the additional files generated:
ffmpeg -vcodec rawvideo -f rawvideo -pix_fmt rgb565 -s 1024x768 -i movie.raw -f image2 -vcodec png image%d.png
Instead of a file, If you have an rgb565 stream, you may attempt to direct the data to stdin of ffmpeg and accomplish the same. In such a case, instead of "-i image.raw", you can use "-i -":
firstCommand | ffmpeg -vcodec rawvideo -f rawvideo -pix_fmt rgb565 -s 1024x768 -i - -f image2 -vcodec png image%d.png
firstCommand should be sending rgb565 raw video data to the standard output of it. We are just redirecting such data to ffmpeg. A trivial example is "cat movie.raw" used in the place of firstCommand.
This was not an easy find! Enjoy.