Systems and methods for selectively screening image data

• US 9,578,207 B1
• Filed: 09/30/2015
• Issued: 02/21/2017
• Est. Priority Date: 09/30/2015
• Status: Expired due to Fees

• Current Assignee: CSR Imaging US, LP
• Original Assignee: CSR Imaging US, LP
• Inventors: Andree, Fred William, Epstein, Neil Brad, Lee, Sung-Chu
• Primary Examiner(s): Nguyen, Madelein
• Application Number:
  US14/871,149
• Time in Patent Office: 510 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: H04N 1/40062 Discrimination between different image types, e.g. two-tone, continuous tone
• CPC Class Codes: H04N 1/4052 by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions
• CPC Class Codes: H04N 1/4055 producing a clustered dots or a size modulated halftone pattern
• CPC Class Codes: H04N 1/4092 Edge or detail enhancement
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening
• CPC Class Codes: H04N 1/58 Edge or detail enhancement; Noise or error suppression, e.g. colour misregistration correction H04N1/62 takes precedence
• CPC Class Codes: H04N 1/6005 with luminance or chrominance signals, e.g. LC1C2, HSL or YUV
• CPC Class Codes: H04N 2201/0094 Multifunctional device, i.e. a device capable of all of reading, reproducing, copying, facsimile transception, file transception

Abstract

Various embodiments are directed to methods, systems, and devices for improving the quality of image data for printing by a printer having relatively low resolution capabilities. Image data may be scanned, captured or otherwise received. The image data may be received in bands, chunks, blocks, portions, regions, or its entirety. An edge detector is subsequently employed to detect a location of edges in a region of the received image data. For image data pixels that are located in or close to a detected edge, a first screen is applied to modify these pixels to compensate for printing at or near the detected edge. Otherwise, a second image screen is applied to modify pixels for printing that are not close to a detected edge. The first screen may be an error diffusion screen or a threshold screen. The second screen may be a halftone screen.

Claims

1. A method for processing image data for printing by a printing device, comprising:

receiving the image data;

employing an edge detector to determine when one or more edges are located in one or more regions of the image data;

when one or more edges is detected in one or more regions of the image data, iteratively performing actions for each pixel in the one or more regions of the image data, including;

determining a gradient of a pixel in the one or more regions of image data;

comparing the gradient of the pixel to a first screen threshold, wherein a first screen is selected for the pixel having an affirmative comparison to the selected first screen threshold and a second screen is selected for the pixel having a negative comparison to the first screen threshold;

for the pixel having the affirmative comparison, determining one or more screened pixel values based on one or more pixel values included in the pixel and the first selected screen; and

for the pixel having the negative comparison, determining the one or more screened pixel values based on one or more pixel values included in the pixel and the second selected screen; and

generating screened image data based on the one or more screened pixel values, wherein the screened image data is employed to print an screened image at the printing device.

2. The method of claim 1, wherein employing an edge detector further comprises generating a representation of the image data in a color space for detecting one or more edges located in one or more regions of the image data.

3. The method of claim 1, wherein employing an edge detector further comprises generating a representation of the image data in one or more luma channels for detecting one or more edges located in one or more regions of the image data.

4. The method of claim 1, wherein the first screen is one of:

an error diffusion screen or a threshold screen.

5. The method of claim 1, wherein the second screen is a halftone screen.

6. The method of claim 1, wherein the method further comprises:

determining a halftone dot resolution of the image data based on one or more tone continuities of the image data; and

determining a coarseness of the edge detector based on the halftone dot resolution;

determining one or more edge kernels based on the coarseness of the edge detector; and

locating the one or more edges in the image data based on the one or more edge kernels and one or more pixel values of each of the pixels in the one or more regions of the image data.

7. The method of claim 1, further comprising:

determining one or more screening weights based on the gradient of the pixel; and

determining the one or more screened pixel values based on the first screen, the second screen, the one or more screening weights and one or more other pixel values included in one or more neighboring pixels of the pixel.

8. The method of claim 1, wherein the method further comprising:

for at least a portion of the pixels in the one or more regions of the image data, determining one or more vertical gradients based on a convolution of a vertical edge kernel with the one or more pixel values included the portion of the pixels;

for the portion of the pixels, determining one or more horizontal gradients based on a convolution of a horizontal edge kernel with the one or more pixel values included in the portion of the pixels;

for the portion of the pixels, determining one or more gradient magnitudes based on a combination of the one or more vertical gradients and the one or more horizontal gradients;

locating the one or more edges based on the one or more gradient magnitudes and a second screen threshold.

9. The method of claim 1, further comprising:

receiving the image data in a first representation in an additive color space;

generating a second representation of the image data in a subtractive color space; and

generating the screened image data, wherein the screened image data is represented in the subtractive color space.

10. An integrated circuit for processing image data for printing by a printing device, comprising:

an input circuit to receive the image data;

an edge detector for determining when one or more edges are located in one or more regions of the image data;

a logic circuit for performing actions, including;

when one or more edges is detected in one or more regions of the image data, iteratively performing actions for each pixel in the one or more regions of the image data, including;

determining a gradient of a pixel in the one or more regions of image data and a closest edge of the one or more edges;

comparing the gradient of the pixel to a first screen threshold, wherein a first screen is selected for the pixel having an affirmative comparison to the selected first screen threshold and a second screen is selected for the pixel having a negative comparison to the first screen threshold;

for the pixel having the affirmative comparison, determining one or more screened pixel values based on one or more pixel values included in the pixel and the first selected screen; and

for the pixel having the negative comparison, determining one or more screened pixel values based on one or more pixel values included in the pixel and the second selected screen; and

an output circuit to generate screened image data based on the one or more screened pixel values, wherein the screened image data is employed to print an screened image at the printing device.

11. The integrated circuit of claim 10, wherein employing an edge detector further comprises generating a representation of the image data in a color space for detecting one or more edges located in one or more regions of the image data.

12. The integrated circuit of claim 10, wherein employing an edge detector further comprises generating a representation of the image data in one or more luma channels for detecting one or more edges located in one or more regions of the image data.

13. The integrated circuit of claim 10, wherein the first screen is one of:

an error diffusion screen or a threshold screen.

14. The integrated circuit of claim 10, wherein the second screen is a halftone screen.

15. The integrated circuit of claim 10, wherein the method further comprises:

determining a halftone dot resolution of the image data based on one or more tone continuities of the image data; and

determining a coarseness of the edge detector based on the halftone dot resolution;

determining one or more edge kernels based on the coarseness of the edge detector; and

locating the one or more edges in the image data based on the one or more edge kernels and one or more pixel values of each of the pixels in the one or more regions of the image data.

16. The integrated circuit of claim 10, further comprising:

determining one or more screening weights based on the gradient of the pixel; and

determining the one or more screened pixel values based on the first screen, the second screen, the one or more screening weights and one or more other pixel values included in one or more neighboring pixels of the pixel.

17. The integrated circuit of claim 10, wherein locating the one or more edges includes:

for at least a portion of the pixels in the one or more regions of the image data, determining one or more vertical gradients based on a convolution of a vertical edge kernel with the one or more pixel values included the portion of the pixels;

for the portion of the pixels, determining one or more horizontal gradients based on a convolution of a horizontal edge kernel with the one or more pixel values included in the portion of the pixels;

for the portion of the pixels, determining one or more gradient magnitudes based on a combination of the one or more vertical gradients and the one or more horizontal gradients;

locating the one or more edges based on the one or more gradient magnitudes and a second screen threshold.

18. The integrated circuit of claim 10, further comprising:

receiving the image data in a first representation in an additive color space;

generating a second representation of the image data in a subtractive color space; and

generating the screened image data, wherein the screened image data is represented in the subtractive color space.

19. A printer device that processes image data for printing, comprising:

an input circuit to receive the image data;

an edge detector for determining when one or more edges are located in one or more regions of the image data;

a logic circuit for performing actions, including;

when one or more edges is detected in one or more regions of the image data, iteratively performing actions for each pixel in the one or more regions of the image data, including;

determining a distance between a pixel in the one or more regions of image data and a closest edge of the one or more edges;

comparing the gradient of the pixel to a first screen threshold, wherein a first screen is selected for the pixel having an affirmative comparison to the selected first screen threshold and a second screen is selected for the pixel having a negative comparison to the first screen threshold;

for the pixel having the affirmative comparison, determining one or more screened pixel values based on one or more pixel values included in the pixel and the first selected screen; and

for the pixel having the negative comparison, determining one or more screened pixel values based on one or more pixel values included in the pixel and the second selected screen; and

an output circuit to generate screened image data based on the one or more screened pixel values; and

a printing assembly that is employed to print an screened image based on the screened image data.

20. The printer device of claim 19, wherein employing an edge detector further comprises one or more of:

generating a representation of the image data in a color space for detecting one or more edges located in one or more regions of the image data;

or

generating a representation of the image data in one or more luma channels for detecting one or more edges located in one or more regions of the image data.