Encoding information in printed images by decreasing grayscale pixel values exceeding threshold

Patent metadata

Field	Value
Publication number	US-10791239-B2
Application number	US-201816605600-A
Country	US
Kind code	B2
Filing date	Jun 15, 2018
Priority date	Mar 20, 2018
Publication date	Sep 29, 2020
Grant date	Sep 29, 2020

Abstract

In an example method, a dot pattern of pixels including information to be encoded across an image is mapped to a corresponding subset of the grayscale source pixels corresponding to the image to be printed. A value of a grayscale pixel in the subset of the grayscale source pixels is modified based on based on a predetermined threshold pixel value. The value of the grayscale pixel is decreased in response to detecting that the predetermined threshold pixel value is exceeded. The clipping channel color is used to detect the dot pattern of pixels. The image including the subset of pixels with modified values is printed.

First claim

What is claimed is:

1. A method comprising:
mapping a dot pattern of pixels comprising information to be encoded across an image to a corresponding subset of grayscale source pixels corresponding to the image;
modifying a value of a grayscale pixel in the subset of the grayscale source pixels based on a predetermined threshold pixel value, wherein the value of the grayscale pixel is decreased in response to detecting that the predetermined threshold pixel value is exceeded; and
printing the image comprising the subset of pixels with modified values.

2. The method of claim 1 , wherein the predetermined threshold pixel value is greater than half of a highest pixel value to compensate for a printer dot gain.

3. The method of claim 1 , wherein the value of the grayscale pixel is increased in response to detecting that the predetermined threshold pixel value is not exceeded.

4. The method of claim 1 , comprising passing a value of a second grayscale pixel corresponding to the subset of grayscale source pixels without modification in response to detecting that the value of the grayscale source pixel is zero.

5. The method of claim 1 , wherein modifying the value of the grayscale pixel comprises using a lookup table to determine a replacement value for the grayscale pixel.

6. An apparatus comprising:
a receiver to receive a set of grayscale source pixels corresponding to an image to be printed and a dot pattern of pixels comprising information to be encoded across the image;
a pattern mapper to map the dot pattern of pixels to a corresponding subset of the grayscale source pixels;
a pixel modifier to modify a value of a grayscale pixel in the subset of the grayscale source pixels based on a predetermined threshold pixel value, wherein the value of the grayscale pixel is to be decreased in response to detecting that the predetermined threshold pixel value is exceeded; and
a printer to print the image comprising the subset of pixels with modified values.

7. The apparatus of claim 6 , wherein the predetermined threshold pixel value is greater than half of a highest pixel value to compensate for a printer dot gain.

8. The apparatus of claim 6 , wherein the pixel modifier is to increase the value of the grayscale pixel in response to detecting that the predetermined threshold pixel value is not exceeded.

9. The apparatus of claim 6 , wherein the pixel modifier is to pass the value of a second grayscale pixel corresponding to the subset of grayscale source pixels without modification in response to detecting that the value of the grayscale source pixel is zero.

10. The apparatus of claim 6 , comprising a lookup table to be used to determine a replacement value for the grayscale pixel.

11. A non-transitory machine-readable storage medium encoded with instructions executable by a processor, the machine-readable storage medium comprising instructions to direct the processor to:
receive a set of grayscale source pixels corresponding to an image to be printed and a dot pattern of pixels comprising information to be encoded across the image;
map the dot pattern of pixels to a corresponding subset of the grayscale source pixels;
modify a value of a grayscale pixel in the subset of the grayscale source pixels based on a predetermined threshold pixel value, wherein the value of the grayscale pixel is to be decreased in response to detecting that the predetermined threshold pixel value is exceeded; and
print the image comprising the subset of pixels with modified values.

12. The non-transitory machine-readable storage medium of claim 11 , comprising instructions to direct the processor to set the predetermined threshold pixel value greater than half of a highest pixel value to compensate for a printer dot gain.

13. The non-transitory machine-readable storage medium of claim 11 , comprising instructions to direct the processor to increase the value of the grayscale pixel in response to detecting that the predetermined threshold pixel value is not exceeded.

14. The non-transitory machine-readable storage medium of claim 11 , comprising instructions to direct the processor to pass a value of a second grayscale pixel corresponding to the subset of grayscale source pixels in response to detecting that the value of the grayscale source pixel is zero.

15. The non-transitory machine-readable storage medium of claim 11 , further comprising instructions to direct the processor to use a lookup table to determine a replacement value for the grayscale pixel.

Assignees

• Hewlett Packard Development Co

Inventors

• Ulichney Robert
• Gaubatz Matthew D

Classifications

• H04N1/32309 Primary

  in colour image data · CPC title

• H04N1/32208

  involving changing the magnitude of selected pixels, e.g. overlay of information or super-imposition (H04N1/32219, H04N1/32224 take precedence) · CPC title

• H04N1/32352

  Controlling detectability or arrangements to facilitate detection or retrieval of the embedded information, e.g. using markers (for decoding, detection or retrieval operations H04N1/32149 and subgroups take precedence) · CPC title

• G06K15/1881

  Halftoning (halftoning of still images in general H04N1/405, H04N1/52) · CPC title

• H04N1/32256

  in halftone data · CPC title