Multibit digital halftoning, indexing 2D and 3D lookup tables
View Patent ↗Digital halftoning processes for producing a halftone image include, for each pixel in the image: indexing a two-dimensional look up table using a position of the pixel, identifying a threshold value for the pixel from the two-dimensional look up table, creating an index that indexes a three-dimensional lookup table using the threshold value and the position of the pixel, and obtaining an output value for the pixel from the three-dimensional look up table via the index. The digital halftoning processes also produce a halftone representation of the image from output values for corresponding pixels.
1. A method for implementing digital halftoning of an image, the method comprising:
for each pixel in the image:
indexing a two-dimensional look up table using a position of the pixel;
identifying a threshold value for the pixel from the two-dimensional look up table;
creating an index that indexes a three-dimensional lookup table using the threshold value and the position of the pixel; and
obtaining an output value for the pixel by indexing the three-dimensional look up table via the index; and
producing a halftone representation of the image from output values for corresponding pixels,
wherein the threshold value is a mean of a set of gray levels used to output to a halftone image.
2. The method of claim 1 , wherein the image is a scanned image representing a two-dimensional array of contone pixels.
3. The method of claim 1 , wherein the index is created by calculating a difference between the position of the pixel and a corresponding threshold value, and scaling a result of the calculating by a constant factor.
4. The method of claim 3 , wherein the constant factor is a range of threshold values to which pixel positions are compared.
5. The method of claim 1 , further comprising:
outputting the halftone representation of the image to a printing device.
6. The method of claim 1 , further comprising:
outputting the halftone representation of the image to a computer display screen.
7. A system for implementing digital halftoning of an image, comprising:
a computer processing device; and
a halftoning engine executing on the computer processing device, the halftoning engine implementing a method, comprising:
for each pixel in the image:
indexing a two-dimensional look up table using a position of the pixel;
identifying a threshold value for the pixel from the two-dimensional look up table;
creating an index that indexes a three-dimensional lookup table using the threshold value and the position of the pixel; and
obtaining an output value for the pixel by indexing the three-dimensional look up table via the index; and
producing a halftone representation of the image from output values for corresponding pixels,
wherein the threshold value is a mean of a set of gray levels used to output to a halftone image.
8. The system of claim 7 , wherein the image is a scanned image representing a two-dimensional array of contone pixels.
9. The system of claim 7 , wherein the index is created by calculating a difference between the position of the pixel and a corresponding threshold value, and scaling a result of the calculating by a constant factor.
10. The system of claim 9 , wherein the constant factor is a range of threshold values to which pixel positions are compared.
11. The system of claim 7 , wherein the method further comprises:
outputting the halftone representation of the image to a printing device.
12. The system of claim 7 , wherein the method further comprises:
outputting the halftone representation of the image to a computer display screen.
13. A computer program product for implementing digital halftoning of an image includes a non-transitory computer readable storage medium having computer readable program code embodied therewith, the computer readable program code configured to implement a method, the method comprising:
for each pixel in the image:
indexing a two-dimensional look up table using a position of the pixel;
identifying a threshold value for the pixel from the two-dimensional look up table;
creating an index that indexes a three-dimensional lookup table using the threshold value and the position of the pixel; and
obtaining an output value for the pixel by indexing the three-dimensional look up table via the index; and
producing a halftone representation of the image from output values for corresponding pixels,
wherein the threshold value is a mean of a set of gray levels used to output to a halftone image.
14. The computer program product of claim 13 , wherein the image is a scanned image representing a two-dimensional array of contone pixels.
15. The computer program product of claim 13 , wherein the index is created by calculating a difference between the position of the pixel and a corresponding threshold value, and scaling a result of the calculating by a constant factor.
16. The computer program product of claim 15 , wherein the constant factor is a range of threshold values to which pixel positions are compared.
17. The computer program product of claim 13 , wherein the method further comprises:
outputting the halftone representation of the image to a printing device.
18. The computer program product of claim 13 , wherein the method further comprises:
outputting the halftone representation of the image to a computer display screen.