Tone correction for multi-level halftoned images
First Claim
1. An image reproducing device, comprising:
- means for producing image values for individual picture elements of an image;
an image generating device for producing a visible image, wherein each picture element of the visible image has a display value that can be at one of multiple intensity levels;
a halftone processor for converting said image values into display values at said multiple intensity levels;
a first correcting device for correcting said image values to compensate for non-linearities in the display values caused by said halftone processor; and
a second correcting device for correcting individual display values to compensate for non-linearities of said display values over a range of said multiple intensity levels.
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Accused Products
Abstract
A multi-level image output device performs correction of pixel values which have undergone halftone processing to compensate for non-linearities. This correction is carried out by means of a tonal reproduction transfer function, which linearizes the output values from a halftone processor before they are applied to an image generator, such as a laser modulator. By rectifying non-linear intensity of individual pixels, images can be generated with a smoother grayscale gradient. The function of the post-halftone correction can be combined with a modulator, to achieve an economy of components which make up the output device. As a further feature, a plurality of post-halftoning correction devices can be provided. One of these devices is selected to correct the data values produced by halftone processing, in dependence upon the values of neighboring pixels in an image.
23 Citations
20 Claims
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1. An image reproducing device, comprising:
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means for producing image values for individual picture elements of an image; an image generating device for producing a visible image, wherein each picture element of the visible image has a display value that can be at one of multiple intensity levels; a halftone processor for converting said image values into display values at said multiple intensity levels; a first correcting device for correcting said image values to compensate for non-linearities in the display values caused by said halftone processor; and a second correcting device for correcting individual display values to compensate for non-linearities of said display values over a range of said multiple intensity levels. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 18, 19)
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10. In an image reproducing device of the type in which each picture element of an image can be reproduced at one of multiple levels, a method for generating a halftoned image, comprising the steps of:
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generating image values for the picture elements of an image, wherein each image value represents one of N levels; halftone processing said image values to produce corresponding display values, wherein each display value represents one of M levels and N>
M>
2;correcting said image values to compensate for non-linearities in the display values caused by said halftone processing; correcting individual display values to compensate for non-linearities in said display values over said M levels; and generating a visible image in accordance with the corrected display values. - View Dependent Claims (11, 12, 20)
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13. In an image reproducing device of the type in which individual pixels are reproduced with an intensity value that can occupy one of multiple levels in a range of intensity values, a halftone processor comprising:
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means for converting image data into display values commensurate with the number of levels in said range; and a correcting device for correcting said display values to compensate for non-linearities of said display values over said range of intensity values. - View Dependent Claims (14)
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15. An image reproducing device, comprising:
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means for producing image values for individual picture elements of an image; an image generating device for producing a visible image, wherein each picture element of the visible image has a display value that can be at one of multiple intensity levels; a halftone processor for converting said image values into display values at said multiple intensity levels; a pre-halftone correcting device for correcting said image values to compensate for non-linearities in the display values caused by said halftone processor; at least two post-halftone correcting devices for correcting said display values to compensate for non-linearities of said display values over a range of said multiple intensity levels; and means for selecting one of said post-halftone correcting devices on the basis of display values for picture elements that are adjacent to a picture element whose display value is being corrected. - View Dependent Claims (16, 17)
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Specification