Gradient direction calculation device

Patent metadata

Field	Value
Publication number	US-2020005484-A1
Application number	US-201916456276-A
Country	US
Kind code	A1
Filing date	Jun 28, 2019
Priority date	Jun 29, 2018
Publication date	Jan 2, 2020
Grant date	—

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, including:
an element gradient vector calculation unit that 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 that 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 that determines comparison results by comparing each of the ratios of magnitudes of the two element gradient vectors with a predetermined threshold; and a gradient direction determination unit that determines a gradient direction corresponding to a combination of the positive/negative signs and the comparison results.

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

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

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

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

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

7 . The gradient direction calculation device according to claim 2 , wherein
the predetermined ratio is tan(22.5°) or an approximated value thereof.

8 . The gradient direction calculation device according to claim 2 , wherein
the predetermined ratio 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 ratio comparison unit 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 element gradient vectors, multiplies the numerator by a magnitude of the other element gradient vector, and determines the comparison results according to the sign of a value obtained after summing the products.

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

• G06T2207/30196

  Human being; Person · CPC title

• G06F18/245

  relating to the decision surface · CPC title