I am making an XNA application where I capture the screenshot from a webcam 4 times a second and then I try to convert it into an Boolean array when the pixel color Red is below
The answer provided by Hans Passant is correct, it is better to use LockBits and process the data all at once.
You might also try writing a shader that thresholds the data and thereby utilize the power of the GPU to parallel-process the input image stream much, much faster.