Screening method for a rendering device having restricted density resolution

Claim 1

A method for rendering an image on a carrier by a rendering system, comprising the steps of: establishing microdots on the carrier, each microdot being addressable by an address (x,y); representing the image by one pixel per microdot, each pixel having as information the address (x,y) and an image signal I x ,y ; partitioning by a screen all microdots in partitions of identical screen cells, each screen cell comprising M (M integer and M>1) microdots R i (i=1. . . M); associating each microdot R i with a pixel tone curve L i , for transforming the image signal I x ,y to an energy level E; determining for each pixel the microdot R i from the address (x,y) and transforming the image signal I x ,y by the corresponding pixel tone curve L i , to a suitable energy level E; converting by the rendering system the energy level E to a density level on the microdot having address (x,y); wherein there are N (N integer and N>2) energy levels E j (i=1. . . N) ordered in ascending or descending energy level order, and selecting an index S (1<S<N) such that: E 1 is a non-marking and stable energy level; E s . . . E N are marking and stable energy levels; and all other energy levels are marking and non-stable.

Claim 2

A method for rendering an image on a carrier by a rendering system, comprising the steps of: establishing microdots on the carrier, each microdot being addressable by an address (x,y); representing the image by one pixel per microdot, each pixel having as information the address (x,y) and an image signal I x ,y ; partitioning by a screen all microdots in partitions of identical screen cells, each screen cell comprising M (M integer and M>1) microdots R i (i=1. . . M); associating each microdot R i with a pixel tone curve L i , for transforming the image signal I x ,y to an energy level E; determining for each pixel the microdot R i from the address (x,y) and transforming the image signal I x ,y by the corresponding pixel tone curve L i , to a suitable energy level E; converting by the rendering system the energy level E to a density level on the microdot having address (x,y); wherein there are N (N integer and N>2) energy levels E j (i=1. . . N) ordered in ascending or descending energy level order, and selecting an index S (1<S<N) such that: E 1 is a non-marking and stable energy level; E s . . . E N are marking and stable energy levels; and all other energy levels are marking and non-stable.

Claim 8

The method according to claims 5 or 6, wherein the fraction. is 15 percent.

Claim 10

The method according to any of claims 4, 5 or 8, wherein exclusively E s is selected as stable marking energy level.

Claim 11

The method according to any of claims 2, 3, 4, 5 or 8, wherein the density D S is obtained by driving all microdots of the carrier by the energy level E s .

Claim 12

A method for rendering an image on a carrier by a rendering system, comprising the steps of: establishing microdots on the carrier, each microdot being addressable by an address (x,y); representing the image by one pixel per microdot, each pixel having as information the address (x,y) and an image signal I x ,y ; partitioning by a screen all microdots in partitions of identical screen cells, each screen cell comprising M (M integer and M>1) microdots R i (i=1. . . M); associating each microdot R i with a pixel tone curve L i , for transforming the image signal I x ,y to an energy level E; determining for each pixel the microdot R i from the address (x,y) and transforming the image signal I x ,y by the corresponding pixel tone curve L i , to a suitable energy level E; converting by the rendering system the energy level E to a density level on the microdot having address (x,y); wherein the pixel tone curves L i transform each value of the image signal to an energy level that causes a micro density that is proportional to an area within the corresponding microdot R i , wherein the area is defined as that portion of the microdot R i that is covered by one or more bands, of which the width is proportional to the density level represented by the image signal, have the same distance with respect to each other and are positioned and oriented such that the center lines continuously connect over neighboring screen cells.

Claim 13

A method for rendering an image on a carrier by a rendering system, comprising the steps of: establishing microdots on the carrier, each microdot being addressable by an address (x,y); representing the image by one pixel per microdot, each pixel having as information the address (x,y) and an image signal I x ,y ; partitioning by a screen all microdots in partitions of identical screen cells, each screen cell comprising M (M integer and M>1) microdots R i (i=1. . . M); associating each microdot R i with a pixel tone curve L i , for transforming the image signal I x ,y to an energy level E; determining for each pixel the microdot R i from the address (x,y) and transforming the image signal I x ,y by the corresponding pixel tone curve L i , to a suitable energy level E; converting by the rendering system the energy level E to a density level on the microdot having address (x,y); wherein the pixel tone curves L i transform each value of the image signal to an energy level that causes a micro density that is proportional to an area within the corresponding microdot R i , wherein the area is defined as that portion of the microdot R i that is covered by one or more bands, of which the width is proportional to the density level represented by the image signal, have the same distance with respect to each other and are positioned and oriented such that the center lines continuously connect over neighboring screen cells.

Claim 17

The method according to any of claims 11, 12, 13 or 14, wherein at least one center line passes through the center of at least one microdot.

Claim 18

The method according to any of claims 11, 12, 13 or 14, wherein the center lines do not pass through the center of the microdots.

Claim 19

The method according to any of claims 11, 12, 13 or 14, wherein the center line has a rational tangent.

Claim 20

The method according to any of claims 11, 12, 13 or 14, wherein the vertical distance between two center lines is always rational.

Claim 24

A method for rendering an image on a carrier by a rendering system, comprising the steps of: establishing microdots on the carrier, each microdot being addressable by an address (x,y); representing the image by one pixel per microdot, each pixel having as information the address (x,y) and an image signal I x ,y ; partitioning by a screen all microdots in partitions of identical screen cells, each screen cell comprising M (M integer and M>1) microdots R i (i=1. . . M); associating each microdot R i with a pixel tone curve L i , for transforming the image signal I x ,y to an energy level E; determining for each pixel the microdot R i from the address (x,y) and transforming the image signal I x ,y by the corresponding pixel tone curve L i , to a suitable energy level E; converting by the rendering system the energy level E; to a density level on the microdot having address (x,y); wherein each pixel tone curve is a weighted sum of binary pixel tone curves from a binary screening method with higher resolution.

Claim 25

A method for rendering an image on a carrier by a rendering system, comprising the steps of: establishing microdots on the carrier, each microdot being addressable by an address (x,y); representing the image by one pixel per microdot, each pixel having as information the address (x,y) and an image signal I x ,y ; partitioning by a screen all microdots in partitions of identical screen cells, each screen cell comprising M (M integer and M>1) microdots R i (i=1. . . M); associating each microdot R i with a pixel tone curve L i , for transforming the image signal I x ,y to an energy level E; determining for each pixel the microdot R i from the address (x,y) and transforming the image signal I x ,y by the corresponding pixel tone curve L i , to a suitable energy level E; converting by the rendering system the energy level E; to a density level on the microdot having address (x,y); wherein each pixel tone curve is a weighted sum of binary pixel tone curves from a binary screening method with higher resolution.