Mitigation of tenting deletions in color xerographic printers
AssigneeXerox Corporation
InventorFritz F. Ebner
Life of this patent
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Abstract
A printing system that uses a halftone processor is driven to halftone selected areas of an image based on a selected halftone dot, wherein the halftone dot has the properties of maintaining a dot fill order of a desired dot, while also maintaining a preselected percentage of the dot as untilled space.
Claims11
A method of altering an image representation to prevent tenting deletions in a color printing system receiving image signals represented at d possible levels, by generating printer signals that retain original color characteristics and provide significantly reduced colorant coverage upon printing, where the color printing system includes a halftoning system that generates printer signals adapted to drive a printer to generate a mark on a substrate at one of c possible levels of colorant, where d>c, said halftoning system using a desired screen matrix have N number of thresholds and N number of threshold values in a K.times.L matrix, each threshold corresponding to a printer signal in an image to be printed, said method comprising the steps of:
- determining a percentage of coverage reduction required to mitigate tenting deletions;
- multiplying N number of thresholds by M, a number related to the coverage reduction percentage, to obtain an increase in the number of thresholds in the screen matrix, thereby obtaining M.times.N number of thresholds, while retaining N number of threshold values in the screen matrix;
- setting a percentage of the M.times.N thresholds to a system value preventing printing of corresponding image signals, said percentage related to the coverage reduction percentage;
- printing a image signal for each threshold value which is exceeded in the screen matrix.
A printing system suitable for forming marks on a substrate at one of c possible levels of colorant, and receiving image signals represented at d possible levels, where d>c, and having a halftone processor to reduce the number of levels at which the image is represented from d levels to c levels in order to replicate gray level printing, including:
- a memory, storing a set of halftone threshold level signals, each threshold signal corresponding to a unique location in an halftone cell;
- a comparator, receiving said image signal and one of the halftone threshold signals from the memory, and producing an output signal at one of c possible levels, varying according to the comparison of said halftone threshold signal to said image signal to cause marking at a selected location on a substrate;
- said set of threshold level signals including a plurality of signals grouped in clusters of predetermined size, each cluster having at least a first threshold value varying between a minimum value and a maximum value, and at least a second threshold value preventing mark formation at a corresponding location, said threshold level signals defining a switching order for varying values of gray in which non-fixed values in each cluster are switched among c levels with varying input values.
An image processing system suitable for generating signals adapted to drive a printer to generate a mark on a substrate at one of c possible levels of colorant, receiving image signals represented at d possible levels, where d>c, and including a halftone processor to reduce the number of levels at which the image is represented from d levels to c levels in order to replicate gray level images, said halftoning system responsive to a screen matrix stored in a halftone processor memory, said screen matrix including:
- a set of N threshold level signals including a plurality of signals grouped in clusters of predetermined size, each cluster having at least 1 threshold value preventing mark formation at a corresponding location, and at least 1 varying threshold level signal;
- said threshold signals ordered in said set to defining a switching order responsive to varying values of gray, and in which plural varying values in each cluster are switched among c levels simultaneously.
Dependencies are inferred from the claim text.