Fujitsu M3097DG, Oem Manual

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Image Functions
3-10
3.2.4
Halftone reading
[A.4.7 SET WINDOW command/Image Composition = X’01’]
This scanner supports two types of halftone image, that is Dither and Error Diffusion.
(1) Dither
[A.4.7 SET WINDOW command / Halftone type = X’01’]
This is a way of producing halftone images with white and black pixels. The scanned image is
processed by the unit of group of pixels.
At first a reference table called “dither matrix” is specified. Each element in the matrix (8x8) has a
threshold value of 256 levels. Allocation of threshold values in the dither matrix is called “dither
pattern”. Group of the scanned images are compared with the dither pattern, and each element is
decided whether it is black or white. Number of black pixels corresponds to a level of scale,
producing pseudo grayscale images.
Four built-in dither patterns are available.
(2) Error diffusion
[A.4.7 SET WINDOW command / Halftone type = X’02’]
This is a way of producing halftone (Pseudo grayscale) images with white and black pixels. Optical
density of pixels and its adjacent pixels are totaled and black pixels are repositioned in the order of
density in accordance with relations between adjacent pixels.
This scheme aims to minimize errors between scanned density and printed density on the average.
Density data of adjacent pixels are modified by diffusing errors on the objective pixel into several
pixels to be binarized. This scheme is aimed to keep high levels of grayscale and high resolution,
producing high quality halftone. Especially when dotted halftone images like photos on the
newspaper are scanned, this scheme suppresses moire patterns.
Following parameters are available for this function
The parameters which affects the Halftone image are shown in Table 3.5.