US 6,185,003 B2 · Method and apparatus for printing digital half-tone images

Abstract

A method of reproducing images formed from binary values of basic pixels arranged in a raster, with an electrophotographic printing unit having an electrically chargeable photo-conductive medium, a selectively activatable light source to discharge of the medium and a developing unit for developing the said medium with toner powder. The method processes the digital image data to compensate for properties of the printing unit by: generating two sub-pixels for each basic pixel, where a first sub-pixel always corresponds in value to the value of the associated basic pixel and a second sub-pixel has a value that depends upon the value of the associated basic pixel and upon the values of basic pixels in a predetermined area around the associated basic pixel; and generating control signals to activate the light source in accordance with each of the generated sub-pixels. Initially, the second pixel is given the same value as that of the associated basic pixel. If, however, this value specifies the activation of the light source and the values of basic pixels in the area around the associated basic pixel indicate that there is a transition in that area between an image portion for exposure and one which is not to be exposed, then the value of the second sub-pixel is converted to the value which does not activate the light source.

Claims30

Dependent claims

In an electrophotographic printing unit having at least one electrically chargeable photo-conductive medium, a selectively activatable light source for image-wise discharge of said medium and a developing unit for developing said medium with toner powder, a method of reproducing images formed from binary values of basic pixels arranged in a raster, the method compensating for properties of the printing unit, the method comprising the steps of:

generating a first and a second sub-pixel for each basic pixel of the digital image data, each said first sub-pixel corresponding in value to the associated basic pixel, each said second sub-pixel having a value determined as a function of the value of the associated basic pixel and values of basic pixels in a predetermined area around the associated basic pixel;
and
generating control signals in accordance with the values of the sub-pixels, respectively, to selectively activate the light source and so compensate for properties of the printing unit such that, for at least substantially every basic pixel that is to be exposed and that is immediately adjacent to a transition from a to-be-unexposed pixel to the to-be-exposed basic pixel, said first sub-pixel is set to be exposed and said second sub-pixel is set to be unexposed.

An apparatus for reproducing an image, comprising:

a first generator for generating digital image data in the form of binary values of basic pixels arranged in a raster;
an electrophotographic printing unit for reproducing an image on an image support on the basis of processed digital image data, the printing unit having at least one electrically chargeable photo-conductive medium, a selectively activatable light source for image-wise discharge of the said medium and a developing unit for developing said medium with toner powder;
a processing unit for receiving digital image data from the first generator, for generating a first sub-pixel and a second sub-pixel for each basic pixel, for setting the first sub-pixel to a value equal to the value of the associated basic pixel, and for setting the second sub-pixel to a value dependent upon the value of the associated basic pixel and values of basic pixels in a predetermined area around the associated basic pixel;
and
a control unit for delivering control signals to selectively activate the light source in accordance with each of the sub-pixels in the processed image data and to compensate for properties of the printing unit such that, for at least substantially every basic pixel that is to be exposed and that is immediately adjacent to a transition from a to-be-unexposed pixel to the to-be-exposed basic pixel, said first sub-pixel is set to be exposed and said second sub-pixel is set to be unexposed.

2 more elements

Dependencies are inferred from the claim text.

Method and apparatus for printing digital half-tone images

Life of this patent

Method and apparatus for printing digital half-tone images

Life of this patent

Abstract

Claims30