1. A method of estimating a halftone image from an original binary image formed of an array of a plurality of pixels, each of said pixels having one of two different components characteristic of a binary image, comprising the steps of: (a) selecting a group of differently configured scanning area units ("SAU's"), each of said SAU's being adapted to enclose a portion of the original binary image having a predetermined number of pixels of said array to be represented with a halftone level; (b) selecting a first target pixel from among the array of a plurality of pixels; (c) choosing one of said group of SAU's; (d) setting said chosen SAU onto a portion of the original binary image which includes said first target pixel; (e) obtaining a counted value of the number of pixels in the portion of the original binary image enclosed within said chosen SAU which have the same one of the two characteristic components of a binary image; (f) assigning a halftone level related to said counted value to each of the pixels in the portion of the original binary image enclosed within the chosen SAU; (g) converting the assigned halftone level into a converted binary image with a threshold value matrix, said threshold vlaue matrix having a plurality of threshold values corresponding in number to the predetermined number of pixels in the portion of the original binary image enclosed within the chosen SAU; (h) comparing an image pattern of the converted binary image with that of the portion of the original binary image enclosed by said chosen SAU to obtain a comparison result; (i) determining whether the comparison result satisfies a predetermined condition and, if it does, to provide an identified SAU for the first target pixel; (j) if the comparison result does not satisfy the predetermined condition of step (i) for the chosen SAU, repeating steps (c)-(i) for other SAU's in said group of SAU's chosen in sequence until an identified SAU is found; (k) generating an estimated halftone image for the first target pixel related to the assigned halftone level obtained with the identified SAU in step (f); (l) sequencing to a next target pixel in the array of a plurality of pixels; and (m) repeating steps (c)-(k) for the next target pixel.