Claims
- 1. A method to select a restricted set of L halftone cell types from an ordered set of halftone cell types comprising the following steps:
- selecting a subset of halftone cell types Hj from said ordered set;
- for each selected halftone cell type Hj from said subset, rendering a contiguous zone by repetitive rendering the same halftone cell Hj a plurality of times;
- measuring the reflectance Rj integrated over said plurality of same halftone cells Hj;
- dividing the range of measured reflectances Rj for all selected halftone cell types Hj from said subset in L-1 substantially equally sized reflectance intervals;
- finding a halftone cell type Hk from the ordered set for each reflectance Rk using the measured reflectances Rj for the selected halftone cell types Hj;
- defining the restricted set as being composed of the halftone cells Hk.
- 2. The method of claim 1, wherein the ordered set of halftone cells is constructed from a restricted set of possible energy levels.
- 3. The method of claim 1, wherein the composition of the ordered set comprises following steps:
- establishing a halftone cell from one or more identical elementary halftone cells composed of microdots, having a primary ordering;
- establishing a subordinate ordering for each microdot within the complete halftone cell;
- defining the ordering such that the primary ordering prevails and the subordinate ordering comes in effect when the primary ordering gives equal candidates for halftone cell types.
- 4. The method of claim 3, wherein the subordinate order corresponds to the order of a generalised Bayer matrix over the halftone cell.
- 5. The method of claim 4, wherein the generalised Bayer matrix is a contiguous subsection of the next larger Bayer matrix, covering the halftone cell, with both dimensions being powers of two.
- 6. The method of claim 4, wherein said Bayer matrix is altered by imposing a random permutation on each sub-matrix, having both dimensions being the smallest prime factor of the size of the generalised Bayer matrix.
- 7. The method of claim 1, wherein said ordered set of halftone cell types is generated by the steps of:
- associating with each halftone cell type a halftone cell with at least one micro dot Bx,y having spatial coordinates (x,y) for its relative location within said halftone cell;
- associating a pixel tone curve with every micro dot within said halftone cell for reproduction of an image on a rendering device driven by a set of at least three energy levels Ej;
- computing for every micro dot Rx,y an object function g(x,y,I) as a function of the relative location (x,y) within the halftone cell and an intensity level I of the image, wherein the object function g indicates the order in which an energy level Ej must be increased to an energy level Ej+1;
- adding an error function e(x,y,I) to each object function, to obtain g'(x,y,I) for imposing a subordinate ordering;
- assigning energy levels Ej to pixel tone curves for each micro dot in the order as indicated by the function g'(x,y,I).
Priority Claims (1)
Number |
Date |
Country |
Kind |
94201151.1 |
Apr 1994 |
EPX |
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Parent Case Info
This is a division of application Ser. No. 08/430,081 filed Apr. 27, 1995.
US Referenced Citations (5)
Divisions (1)
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Number |
Date |
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Parent |
430081 |
Apr 1995 |
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