Reduction of moire by adaptively selecting a smoothing filter fo

Details Reduction of moire by adaptively selecting a smoothing filter fo Reduction of moire by adaptively selecting a smoothing filter fo

1993-12-03

1995-04-18

Coles, Sr., Edward

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

355445, 355463, 355462, 355467, 355457, 355456, 355464, 355433, 355455, 382 22, 382 54, 382 56, H04N 140, H04N 138, G06K 940, G06K 936

Patent

active

054083370

ABSTRACT:
An image processing apparatus in which a moire occurring in a half tone area can be eliminated by a suitable filter. A plurality of data blocks comprising N*N pixel data are transformed by means of a two-dimensional orthogonal transform so as to obtain an N*N matrix transformation factor block. An evaluation block is prepared which comprises N*N transformation factors each of which is the mean value of the absolute values of corresponding factors from a data block being considered and data blocks surrounding the data block to be determined. Mean values A[i] and B[i] (i=0 to L-1) of predetermined transformation factors are calculated, A[i] being mean values of factors included in a number L of first areas consecutively positioned along a diagonal line of the evaluation block, B[i] being mean values of factors included in a number L of second areas positioned adjacent to and lower in frequency to the corresponding first areas. A filter selection signal is generated which corresponds to the number i when a condition is satisfied where A[i]>B[i] and A[i]>threshold value th1. The pixel data corresponding to the evaluation block is smoothed by the selected filter.

REFERENCES:
patent: 5287200 (1994-02-01), Sullivan et al.
patent: 5359676 (1994-10-01), Fan
patent: 5371611 (1994-12-01), Kato et al.

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