Method of spatially thresholding a discrete color image

Details Method of spatially thresholding a discrete color image Method of spatially thresholding a discrete color image

1985-06-20

1987-06-16

Goldberg, E. A.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

358261, 382 56, H04N 712, H04N 100, G06K 936

Patent

active

046739777

ABSTRACT:
A method is disclosed for thresholding the luminance component of color picture elements (pels) prior to compression. The method is most effective when used with discrete color images, such as documents having areas of nominally constant color. The method uses spatial information rather than histogram information to threshold the image data. Each scan line is defined as having a series of pel runs. A pel is considered to be in a run if its luminance is within a certain range of an average luminance based on preceding pels. Each run may end in a transition region wherein the luminance of each pel differs from the luminance of the preceding pel by more than a predetermined amount. Where a transition region is found, a local threshold is set based on the average luminance of the preceding run and of the following pel. All pels in the transition region are assigned a luminance value equal either to the average luminance of the preceding run or the actual luminance of the following pel.

REFERENCES:
patent: 4189711 (1980-02-01), Frank
patent: 4476495 (1984-10-01), Fujisawa et al.
patent: 4501016 (1985-02-01), Persoon et al.
patent: 4542411 (1985-09-01), Imanaka et al.

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