you can access to a specific pixel by typing : figure_name(x_pos,y_pos) .
In the MATLAB workspace, most images are represented as two-dimensional arrays (matrices), in which each element of the matrix corresponds to a single pixel in the displayed image. (from Matlab documentation )
This matrix can be represented in several types as double, uint8, uint16. It can also be RGB, intensity, or indexed types.
I highly recommend reading to understand the differences.