1. An image signal processor comprising: a central processing unit (CPU) configured to receive image data and positional information of phase detection pixels from an imaging device, extract first phase detection pixel data and second phase detection pixel data from the image data using the positional information of the phase detection pixels, compute first phase graphs from the first phase detection pixel data based upon moving a first window, compute second phase graphs from the second phase detection pixel data based upon moving a second window, compute disparities between the first phase graphs and the second phase graphs, and generate a depth map based upon the disparities, wherein: a size of the first window is set to be n*m pixels (the n, and m are the natural number more than 2), using the first window present at a first position at a first time, each first axis value of each of the first phase graph for the first window is computed as a combination of values of each column of the first window or a combination of values of each row of the first window, a size of the second window is set to be n*m pixels (the n, and m are the natural number more than 2), using the second window present at the first position at the first time, each first axis value of each of the second phase graph for the second window is computed as a combination of values of each column of the second window or a combination of values of each row of the second window.