Just follow the trail of data in your variables:

image -> bitmapImageRep -> width, height -> myBitmapContext -> myImage -> bitmapRep -> producedImage

You see that the only thing you take from the original image is its width & height. No where do you refer to the data in the image.

Clearly you need to do a lot more reading. Maybe google for more examples, or download open source programs that might be doing similar things, etc.