1. A method of creating a histogram of an image signal matrix representative of a radiographic image having a plurality of pixels, said method comprising the steps of: i) scanning a stimulable phosphor sheet carrying the radiation image with stimulating rays; ii) detecting for each pixel the light emitted after stimulation; iii) converting for each pixel the detected light into electrical signals; iv) collecting a subset of said electrical signals by statistical sampling relative to discrete, non-clustered pixels, said statistical sampling being performed by the following steps: a) choosing a range of sample distances di; b) deducting from di a range of corresponding pixel numbers ni; c) choosing a value n out of ni; d) generating one random number y within the ni-range; e) defining all sampling lines as follows: locating the initial sample-line (on which the first pixel-samples will be taken) at height y, and defining all next sample-lines by upgrading the position of the initial sample-line by increments of n; f) generating a series of random numbers xj={x1, x2. .. xl} within the same above-mentioned range ni; g) sampling all pixels pj as follows: determining the initial pixel (which will be sampled first) on each line at horizontal position x1 for the first line, x2 for the second line, etc; and defining all next pixels on each line to be sampled by upgrading the initial pixel position xJ by increments of n up to the end of each line to be sampled; v) creating a histogram by means of said subset; vi) displaying said histogram on a monitor; and, vii) using said histogram for the determination of the relevant image window.