1. A system for measuring image blur in a digital image, the digital image having luminance and chrominance components, the system comprising: at least one memory; and at least one processor operative to execute at least one computer program out of the at least one memory: to generate, from at least one of the luminance and chrominance components of the digital image, image pixel data in an image pixel array corresponding to the digital image, the image pixel array having a plurality of pixel locations for pixel values of the image pixel data; to calculate gradient image data in a gradient image array from the image pixel data, the gradient image data representing a plurality of states, the gradient image array having a plurality of state locations for state values of the gradient image data, each of the state values corresponding to a respective gradient value calculated in a specified direction for a respective pair of adjacent pixel locations in the image pixel array; to estimate a plurality of transition probabilities between respective pairs of state values for adjacent state locations disposed in the specified direction throughout the gradient image array; to pool data corresponding to the plurality of transition probabilities to generate a measurement of image blur in the digital image; and to generate an output indicative of the measurement of image blur in the digital image.