Patent ID: 8488138

Claim:
A method for composing a global histogram of values of pixels during transformation of an image on a hardcopy original to an electronic representation of the image by means of an opto-electronic conversion device generating scanlines, said method comprising the steps of: establishing a division of a detection area in stripes, each stripe comprising several scanlines; initializing a candidate histogram and said global histogram; for each stripe: scanning the stripe; composing a local histogram of values of pixels within the stripe; adding the local histogram of values of pixels to the candidate histogram; determining from the local histogram, if the values of pixels in the stripe originate from the hardcopy original; and if it is determined that the values of pixels in the stripe originate from the hardcopy original, both adding the candidate histogram to the global histogram and clearing the candidate histogram; if it is determined that the values of pixels in the stripe do not originate from the hardcopy original, neither adding the candidate histogram to the global histogram nor clearing the candidate histogram, such that, after scanning a subsequent stripe, said candidate histogram still comprises said local histogram and said local histogram becomes part of the global histogram only if it is determined that the values of pixels of said subsequent stripe originate from the hardcopy original; and finalizing the global histogram after scanning the last stripe, wherein the hardcopy original is aligned to a side of the detection area where a first scanline is acquired.