IMAGE PROCESSING
2-32
A229 SM
Dot Screen Determination
The machine determines whether the pixel is in a dot screen area or not. The
process can be adjusted with SP4912-017.
The page is divided into 4 x 4 blocks of pixels. Each block [A] is placed at the
center of a 5 x 3 array of these blocks, and becomes either text or photo,
depending on the other blocks in the 5 x 3 area .
If the number of dot screen blocks in the 5 x 3 area exceeds a threshold, the
central block is determined to be an image area. (The threshold is 2: if two or more
of the blocks in the 5 x 3 area are dot screen, then all the pixels in the central block
are determined to be in an image area.)
Final Evaluation
The final evaluation depends on the result of dot screen and edge determination as
follows.
Dot Screen Edge Final Evaluation
No No Photo
No Yes Text
Yes No Photo
Yes Yes Photo
The type of filtering to be used depends on the result of the final evaluation.
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