Error diffusion of overlapping dots

Claim 2

An error diffusion method for converting gray-scale pixel information into binary data capable of being rendered by dots, which may overlap, each dot having one of two levels of density, said method including the steps of: providing a fixed threshold value; determining which level of density is to be rendered for a first dot, said determination being based upon a comparison of the fixed threshold value with a gray-scale value of pixel information corresponding to the first dot; propagating, to an adjacent dot, at least a portion of any error between the determined density level of the first dot and the fixed threshold value; modifying the propagated error based upon the amount of overlap between the first dot and the adjacent dot and upon the rendered level of the first dot; using the modified error to adjust the gray-scale value of the pixel corresponding to the adjacent dot; and comparing the adjusted gray-scale value with the threshold value to determine which density level is to be rendered for the adjacent dot.

Claim 3

The error diffusion method of claim 1 wherein no modification is made to the propagated error when the first dot is rendered in the lower of the two density levels.

Claim 4

The error diffusion method of claim 1 wherein the modification to the propagated error is a function of the overlapped area to a complete area of the adjacent dot when the first dot is rendered in the higher of the two density levels.

Claim 5

The error diffusion method of claim 1 wherein the modified error is propagated in two directions to two adjacent dots, with the same modified error being used to establish the adjusted gray-scale value for each of the adjacent dots.

Claim 6

The error diffusion method of claim 4 wherein the modified error which is used to establish an adjusted gray-scale value for the adjacent dot is derived from the two dots partially overlapping the adjacent dot.

Claim 7

The error diffusion method of claim 1 wherein steps of the method are repeated so that all of the binary dots to be rendered from the gray-scale pixel information are thresholded using a modified propagation error which is based upon the amount of overlap between adjacent dots and the rendered level of the previous dot.

Claim 8

An error diffusion method for converting gray-scale pixel information into binary data capable of being rendered by dots, which may overlap, each dot having one of two levels of density, said method including the steps of: providing a fixed threshold value; determining which level of density is to be rendered for a first dot, said determination being based upon a comparison of the fixed threshold value with the gray-scale value of pixel information corresponding to the first dot; propagating, to at least two adjacent dots, at least a portion of any error between the determined density level of the first dot and the fixed threshold value; modifying the propagated error when the first dot is rendered in the higher of the two density levels, said modification being based upon the amount of overlap between the first dot and the corresponding adjacent dot; using the modified error to adjust the gray-scale of the pixel corresponding to the adjacent dots; comparing the adjusted gray-scale value with the threshold value to determine which density level is to be rendered for the adjacent dots; and repeating steps of the method so that all of the binary dots to be rendered from the gray-scale pixel information are thresholded using a modified propagation error which is based upon the amount of overlap between adjacent dots and the rendered level of the error propagating dot.

Claim 9

An error diffusion method for converting gray-scale pixel information into binary data capable of being rendered by dots, which may overlap, each dot having one of two levels of density, said method including the steps of: providing a fixed threshold value; determining which level of density is to be rendered for a first dot, said determination being based upon a comparison of the fixed threshold value with the gray-scale value of pixel information corresponding to the first dot; propagating, to at least two adjacent dots, at least a portion of any error between the determined density level of the first dot and the fixed threshold value; modifying the propagated error when the first dot is rendered in the higher of the two density levels, said modification being based upon the amount of overlap between the first dot and the corresponding adjacent dot; using the modified error to adjust the gray-scale of the pixel corresponding to the adjacent dots; comparing the adjusted gray-scale value with the threshold value to determine which density level is to be rendered for the adjacent dots; and repeating steps of the method so that all of the binary dots to be rendered from the gray-scale pixel information are thresholded using a modified propagation error which is based upon the amount of overlap between adjacent dots and the rendered level of the error propagating dot.

Claim 10

Apparatus for converting gray-scale pixel information into binary data capable of being rendered in binary dots which may overlap, each dot having one of two possible density levels, said apparatus comprising: means for thresholding the pixel information by comparing the information with a threshold value to determine which density level should be rendered by a dot corresponding to the pixel information; means for propagating any error produced during the thresholding process from a propagating dot to at least one adjacent dot; and means for affecting the thresholding process for an adjacent dot based at least partially upon the area overlap between the propagating and adjacent dots and the density level of the propagating dot.

Claim 11

Apparatus for converting gray-scale pixel information into binary data capable of being rendered in binary dots which may overlap, each dot having one of two possible density levels, said apparatus comprising: means for thresholding the pixel information by comparing the information with a threshold value to determine which density level should be rendered by a dot corresponding to the pixel information; means for propagating any error produced during the thresholding process from a propagating dot to at least one adjacent dot; and means for affecting the thresholding process for an adjacent dot based at least partially upon the area overlap between the propagating and adjacent dots and the density level of the propagating dot.

Claim 12

The apparatus of claim 8 wherein the affecting means changes the threshold value when the propagating dot is rendered at the higher of the two density levels.

Claim 13

The apparatus of claim 9 wherein the threshold value is changed by an amount proportional to the amount of overlap and a total area of the adjacent dot.

Claim 14

The apparatus of claim 8 wherein the error is propagated in at least two directions to two adjacent dots.

Claim 15

The apparatus of claim 8 wherein the affecting means changes the gray-scale value for the adjacent dot.

Claim 16

The apparatus of claim 8 wherein the error is converted into lightness space before it is propagated.

Claim 17

The apparatus of claim 8 wherein the pixel information for the adjacent dot is converted into lightness space.

Claim 18

Apparatus for converting first gray-scale pixel information provided at a first number of discrete gray levels into second data at a second number of discrete gray levels capable of being rendered by dots which may overlap, the dots having densities according to the second number of discrete gray levels, said first number being greater than said second number, said apparatus comprising: means for thresholding the first pixel information by comparing this information with one or more threshold values to determine which density level should be rendered by a dot corresponding to this pixel information; means for propagating any error produced during the thresholding process from a propagating dot to at least one adjacent dot; and means for affecting the gray-scale value of the adjacent dot based at least partially upon the area overlap between the propagating and adjacent dots and the density level of the propagating dot.

Claim 19

Apparatus for converting first gray-scale pixel information provided at a first number of discrete gray levels into second data at a second number of discrete gray levels capable of being rendered by dots which may overlap, the dots having densities according to the second number of discrete gray levels, said first number being greater than said second number, said apparatus comprising: means for thresholding the first pixel information by comparing this information with one or more threshold values to determine which density level should be rendered by a dot corresponding to this pixel information; means for propagating any error produced during the thresholding process from a propagating dot to at least one adjacent dot; and means for affecting the gray-scale value of the adjacent dot based at least partially upon the area overlap between the propagating and adjacent dots and the density level of the propagating dot.

Claim 20

The apparatus of claim 15 wherein the error is converted into lightness space to linearize the error.

Claim 21

The apparatus of claim 15 wherein the error is converted into uniform color space to linearize the error.

Claim 24

The method of claim 18 wherein the error is defined in terms of lightness space.

Claim 25

The method of claim 18 wherein the error is defined in terms of uniform color space.