Method and apparatus for converting continuous-tone images to bi-level images
AssigneeOki Data Corporation
InventorKoji Urasawa
Life of this patent
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Abstract
A continuous-tone image is converted to a bi-level image by first applying an inverse gamma correction to a threshold matrix, then comparing the gray levels in the continuous-tone image with the corrected threshold values. The threshold matrix may be selected from a library of threshold matrices, and the inverse gamma correction applied by using a gamma correction table selected from a library of such tables. Alternatively, a library containing at least one corrected threshold matrix, to which the inverse gamma correction has already been applied, may be stored.
Claims16
A method of converting a continuous-tone image having more than two gray levels to a bi-level image having only two gray levels, comprising the steps of:
- (a) storing at least one first threshold matrix with a plurality of threshold values;
- (b) applying an inverse gamma correction to the threshold values in said first threshold matrix, thereby obtaining a second threshold matrix with a plurality of corrected threshold values;
- and
- (c) comparing the gray levels in said continuous-tone image with said corrected threshold values, thereby generating said bi-level image.
An apparatus for converting a continuous-tone image having more than two gray levels to a bi-level image having only two gray levels, comprising:
- a corrected dither pattern generator applying an inverse gamma correction to a first threshold matrix having a plurality of threshold values, thereby obtaining a second threshold matrix with corrected threshold values;
- and
- a dither processor, coupled to said corrected dither pattern generator, comparing the gray levels in said continuous-tone image with said corrected threshold values, thereby generating said bi-level image.
A method of converting a continuous-tone image having more than two gray levels to a bi-level image having only two gray levels, comprising the steps of:
- (a) storing at least one corrected threshold matrix having corrected threshold values obtained by applying an inverse gamma correction to a threshold matrix used for converting a gamma-corrected continuous-tone image to a bi-level image;
- and
- (b) comparing the gray levels in said continuous-tone image with said corrected threshold values, thereby generating said bi-level image.
An apparatus for converting a continuous-tone image having more than two gray levels to a bi-level image having only two gray levels, comprising:
- a storage device storing at least one corrected threshold matrix having corrected threshold values obtained by applying an inverse gamma correction to a threshold matrix used for converting a gamma-corrected continuous-tone image to a bi-level image;
- and
- a dither processor coupled to said storage device, comparing the gray levels in said continuous-tone image with said corrected threshold values, thereby generating said bi-level image.
Dependencies are inferred from the claim text.