updating images using multithreading

hello,
          I am facing a problem while updating multiple images on my wpf form. i have two bitmap images an i wish to write the pixel data in these two images in parallel. I created two threads and assign the task. however there is an error...
The calling thread cannot access this object because a different thread owns it.

I understand that  actually my image objects are  handled by main thread and so the background threads are  not able to access them. can anyone knows a way to do the update in parallel . I really need to run the code in parallel as i am capturing images at 30fps. 


thank you