converting a C code to multi threading

I have a code in C language deals with processing image. I need someone to convert the C code to multi thread. The code is allready modularized on each task. All needs to be done is converting few of the tasks to threading. Any person who had worked in multi threading environment in the past can successfully convert the code. The threading implementation is flexible to the programmer's choice with less complexity, no fancy staff. The main job is to spawn the threads of few specific tasks. Details will be provided as shown interest on the project via private messaging.