Gradient direction calculation device

Patent metadata

Field	Value
Publication number	US-11074712-B2
Application number	US-201916456276-A
Country	US
Kind code	B2
Filing date	Jun 28, 2019
Priority date	Jun 29, 2018
Publication date	Jul 27, 2021
Grant date	Jul 27, 2021

Abstract

In a gradient direction calculation device, an element gradient vector calculation unit calculates two mutually perpendicular element gradient vectors with respect to a pixel of interest by using a difference in pixel values in the vicinity of the pixel of interest. A quadrant determination unit determines, based on a combination of positive/negative signs of each of the two element gradient vectors, a quadrant among the four quadrants defined by the two element gradient vectors that contains a gradient direction of the pixel of interest. A ratio comparison unit determines comparison results by comparing each of the ratios of magnitudes of the two element gradient vectors with a predetermined threshold. A gradient direction determination unit determines a gradient direction corresponding to a combination of the positive/negative signs and the comparison results.

First claim

What is claimed is:

1. A gradient direction calculation device that calculates a gradient direction of a pixel, comprising:
a non-transitory memory storing one or more computer programs; and
a processor executing the one or more computer programs to:
calculate two element gradient vectors with respect to a pixel of interest by using a difference in pixel values a vicinity of the pixel of interest, the two element gradient vectors being mutually perpendicular;
determine, based on a combination of signs of the two element gradient vectors, which one of four quadrants defined by the two element gradient vectors contains a gradient direction of the pixel of interest;
determine comparison results by comparing each of ratios of magnitudes of the two element gradient vectors with a predetermined threshold; and
determine a gradient direction corresponding to a combination of the signs and the comparison results.

2. The gradient direction calculation device according to claim 1 , wherein
the processor determines the gradient direction by determining on of eight directions.

3. The gradient direction calculation device according to claim 1 , wherein
the processor calculates the two element gradient vectors by using a difference in pixel values of pixels in each of two diagonal directions in a set of four pixels including the pixel of interest.

4. The gradient direction calculation device according to claim 1 , wherein
the processor calculates one of the two element gradient vectors by using a difference in pixel values of two pixels adjacent to the pixel of interest in a vertical direction, and calculates the other of the two element gradient vectors by using a difference in pixel values of two pixels adjacent to the pixel of interest in a horizontal direction.

5. The gradient direction calculation device according to claim 1 , wherein
the processor determines the gradient direction by using a lookup table that takes as input a combination of the signs and the comparison results.

6. The gradient direction calculation device according to claim 1 , wherein
the processor determines the gradient direction by using a lookup table that takes as input a value obtained by respectively multiplying the signs and the comparison results by predetermined coefficients, and then summing the products.

7. The gradient direction calculation device according to claim 1 , wherein
the predetermined threshold is tan(22.5°) or an approximated value thereof.

8. The gradient direction calculation device according to claim 1 , wherein
the predetermined threshold is expressed as a fraction in which both a denominator and a numerator are expressed as an integer.

9. The gradient direction calculation device according to claim 8 , wherein
the processor sets whichever of the denominator and the numerator that requires a smaller number of bits to be expressed to a negative number, multiplies the denominator by a magnitude of one of the two element gradient vectors, multiplies the numerator by a magnitude of the other of the two element gradient vectors, and determines the comparison results according to the sign of a value obtained after summing the products.

10. A computer-implemented method for calculating a gradient direction of a pixel, the computer-implemented method comprising:
calculating two element gradient vectors with respect to a pixel of interest by using a difference in pixel values in a vicinity of the pixel of interest, the two element gradient vectors being mutually perpendicular;
determining, based on a combination of signs of the two element gradient vectors, which one of four quadrants defined by the two element gradient vectors contains a gradient direction of the pixel of interest;
determining comparison results by comparing each of ratios of magnitudes of the two element gradient vectors with a predetermined threshold; and
determining a gradient direction corresponding to a combination of the signs and the comparison results.

11. The computer-implemented method according to claim 10 , further comprising:
determining the gradient direction by determining one of eight directions.

12. The computer-implemented method according to claim 10 , further comprising:
calculating the two element gradient vectors by using a difference in pixel values of pixels in each of two diagonal directions in a set of four pixels including the pixel of interest.

13. The computer-implemented method according to claim 10 , further comprising:
calculating one of the two element gradient vectors by using a difference in pixel values of two pixels adjacent to the pixel of interest in a vertical direction; and
calculating the other of the two element gradient vectors by using a difference in pixel values of two pixels adjacent to the pixel of interest in a horizontal direction.

14. The computer-implemented method according to claim 10 , further comprising:
determining the gradient direction by using a lookup table that takes as input a combination of the signs and the comparison results.

15. The computer-implemented method according to claim 10 , further comprising:
determining the gradient direction by using a lookup table that takes as input a value obtained by respectively multiplying the signs and the comparison results by predetermined coefficients, and then summing the products.

16. The computer-implemented method according to claim 10 , wherein
the predetermined threshold is tan(22.5°) or an approximated value thereof.

17. The computer-implemented method according to claim 10 , wherein
the predetermined threshold is expressed as a fraction in which both a denominator and a numerator are expressed as an integer.

18. The computer-implemented method according to claim 17 , further comprising:
setting whichever of the denominator and the numerator that requires a smaller number of bits to be expressed to a negative number, multiply the denominator by a magnitude of one of the two element gradient vectors, multiply the numerator by a magnitude of the other of the two element gradient vectors, and determine the comparison results according to the sign of a value obtained after summing the products.

19. A non-transitory computer-readable storage medium having stored therein instructions executable by a processor to cause the processor to perform functions comprising:
calculating two element gradient vectors with respect to a pixel of interest by using a difference in pixel values in a vicinity of the pixel of interest, the two element gradient vectors being mutually perpendicular;
determining, based on a combination of signs of the two element gradient vectors, which one of four quadrants defined by the two element gradient vectors contains a gradient direction of the pixel of interest;
determining comparison results by comparing each of ratios of magnitudes of the two element gradient vectors with a predetermined threshold; and
determining a gradient direction corresponding to a combination of the signs and the comparison results.

20. A gradient direction calculation device for calculating a gradient direction of a pixel, comprising:
a processing unit configured to:
calculate two element gradient vectors with respect to a pixel of interest by using a difference in pixel values in a vicinity of the pixel of interest, the two element gradient vectors being mutually perpendicular;
determine, based on a combination of signs of the two element gradient vectors, which one of four quadrants defined by the two element

Assignees

• Denso Corp

Inventors

• Nomoto Shohei

Classifications

• G06T7/13 Primary

  Edge detection · CPC title

• G06V10/758

  Involving statistics of pixels or of feature values, e.g. histogram matching · CPC title

• G06T7/73 Primary

  using feature-based methods · CPC title

• G06F18/245

  relating to the decision surface · CPC title

• G06V10/50

  by performing operations within image blocks; by using histograms, e.g. histogram of oriented gradients [HoG]; by summing image-intensity values; Projection analysis · CPC title