  Thresholding converts a greyscale image into a binary image, and is thus
often a necessary segmentation step in image processing. For a human viewer
however, thresholding usually has a negative impact on the legibility of
document images. This report describes a simple method for "smearing out" the
threshold and transforming the greyscale image into a different greyscale
image. The method is similar to fuzzy thresholding, but is discussed here in
the simpler context of greyscale transformations and, unlike fuzzy
thresholding, it is independent from the method for finding the threshold. A
simple formula is presented for automatically determining the width of the
threshold spread. The method can be used, e.g., for enhancing images for the
presentation in online facsimile repositories.
