JPS61239377A - Device for detecting angle difference between pictures - Google Patents

Abstract

PURPOSE:To increase the speed for detecting the angle difference between two similar pictures, by utilizing the maximum value of the angle histogram of the maximum changing direction of the picture element value of a picture. CONSTITUTION:The picture element value data of a picture to be collated stored in an image memory 1 are supplied to a space differentiating circuit 2 composed of a 3X3 differentiation calculating window and the maximum changing direction of the picture element value is found. Then the data are supplied to a histogram calculating circuit 3 and become the angle histogram data of density gradient and once stored in a histogram memory 4. A maximum value detecting circuit 5 detects the maximum value of the histogram data of the histogram memory 4 which are successively read out in accordance with the address of an address generating circuit 9 and sends then angle to a subtracting circuit 7. The angle is compared with an angle which gives the maximum of the angle histogram of a reference picture stored in a register 6 at the subtracting circuit 7 and the rotating angle between two picture is detected.

Description

Detailed Description of the Invention [Summary] In a device that detects the angular difference between two congruent, similar, or similar images, the detection speed can be increased by using the maximum value of the angular histogram in the direction of maximum change in one pixel value. The aim is to increase the number of people.

[Industrial application field]

For example, in a seal matching device, which is an applied field of image processing technology, a matching seal impression, that is, a matching image, and a registered seal impression, that is, a reference image, are used as a reference for matching, using techniques such as pattern matching. The information is compared and the consistency between the two is checked.

However, if the angle or orientation of the image to be matched is different from that of the reference image, matching is difficult as is.

Therefore, in a seal verification device or the like, an angular difference detection device between five images is used to match the angles (align the directions) of the two images.

At this time, it is desirable that the angular difference between the two images can be detected in a short time with a small amount of calculation.

[Conventional technology]

FIG. 3 is a principle block diagram of a conventional example of an angular difference detection device between images.

Reference numeral 1 denotes an image memory that stores the density of the image to be compared as a quantized pixel value for each pixel arranged at a constant pitch in a grid pattern.

2 is the image stored in 1 image memory 1 (3 x 3)
A spatial differentiation circuit that scans through a differential calculation window to find the direction of maximum change in density, that is, the spatial differential value, at each pixel.

3 is a histogram calculation circuit that calculates the angle histogram by counting the maximum change direction of the pixel values obtained by the spatial differentiation circuit 2 for each angle.

A first histogram memory 4 stores the angle histogram obtained by the histogram calculation circuit 3 using angles from 0 to 359 degrees as addresses.

A second histogram memory 8 similarly stores an angle histogram obtained in advance from a reference image using angles from 0 to 359 degrees as addresses.

9 is an address generation circuit that generates addresses from 0 to 359;

10 is 1 for each address generated by the address generation circuit 9.
An address conversion circuit that converts the address to an address shifted by 0 to 359 degrees in the variable position.

Reference numeral 11 denotes a difference integration circuit that calculates the integrated value of the absolute value of the difference between the histogram read from the first histogram memory 4 and the angle histogram read from the second histogram memory 8.

Reference numeral 12 denotes an integrated value memory that stores the integrated value, that is, the distance, obtained by the difference integrating circuit 10 using the shift angle shifted by the address conversion circuit 10 as an address.

That is, the angle histogram of the image to be matched stored in the first histogram memory 4 is shifted from 0 to 359 degrees, the distance between each of them and the histogram stored in the second histogram memory 8 is determined, and the minimum The shift amount when the distance is obtained is used as the rotation angle difference between the two images.

[Problem that the invention seeks to solve]

In the conventional example, it is necessary to calculate the distance between two angle histograms 360 times, and in each calculation, it is necessary to calculate the difference between the angle histograms for each angle 360 times. Therefore, there is a problem that the number of calculations becomes enormous.

That is, an object of the present invention is to reduce the enormous amount of calculations in the conventional example.

[Means for solving problems]

FIG. 1 is a block diagram of the principle of the present invention, and FIG. 4 shows the same reference numerals as those of the conventional example.

Reference numeral 5 denotes a maximum value detection circuit that detects the angle corresponding to the maximum value of the angle histogram obtained from the matched image stored in the histogram memory 4.

6 is a register that similarly stores the angle corresponding to the maximum value of the angle histogram obtained in advance from the reference image.

7 is a subtraction circuit that calculates the difference between the angle detected by the maximum value detection circuit 5 and the angle stored in the register 6;
The angle obtained by the subtraction circuit 7 is the rotation angle difference between the image to be matched and the reference image.

[Effect]

That is, the maximum value detection circuit 5 uses the histogram memory 4
Find the maximum value of the angle histogram from.

Detect the address when that value was read.

The difference between the detected value and the angle stored in the register 6 in advance is used as the angular difference between the reference image and the matched image by the subtraction circuit 7.
is output from.

〔Example〕

FIG. 2 is a block diagram of the embodiment, and the maximum value detection circuit 5 is composed of a comparison circuit (COM) 5a, a selection circuit (MPχ) 5b, and a register 5c.

Zero is set in register 5c as an initial value.

The comparison circuit 5a compares the angle value stored in the register 5c with the angle value read from the histogram memory 4, and the selection circuit 5b selects whichever is larger based on the comparison result in the comparison circuit 5a. The angle values along with their addresses are sent to register 5C, which stores them.

As a result, after the address generator 9 finishes reading out all angle histogram values from 0 to 359 degrees, the register 5C detects the maximum value among them and the address, that is, the angle corresponding to that value. The subtraction circuit 7 obtains the difference between the calculated angle and the angle stored in the register 6 in advance.

According to this embodiment, the angular difference between two images can be determined with a calculation amount of 1/360 compared to the conventional example.

〔Effect of the invention〕

As explained above, according to the present invention, the angular difference between two images can be determined with a much smaller amount of calculation compared to the conventional example.

Therefore, for example, the verification speed in a seal verification device can be significantly reduced.

FIG. 2 is a configuration diagram of the embodiment.

FIG. 3 shows a principle block diagram of a conventional example.

In the figure.

1 is an image memory, 2 is a spatial differentiation circuit.

3 is a histogram calculation circuit.

4 is histogram memory.

5 is a maximum value detection circuit, and 6 is a register.

Principle of trap moat example 1υ・7th Ban 3 呵

Claims (1)

[Scope of Claims] A spatial differentiation circuit (2) for determining the direction of maximum change in pixel value for each pixel of an image represented by quantized pixel values for each pixel arranged in a grid shape at a constant pitch; , a histogram calculation circuit (3) that calculates the angle histogram by counting the direction of maximum change in pixel values obtained by the spatial differentiation circuit (2) for each angle; A maximum value detection circuit (5) that detects the angle corresponding to the value, a register (6) that stores the angle corresponding to the maximum value of the angle histogram obtained from the reference image in advance, and an angle detected by the maximum value detection circuit 5. An angular difference detection device between images, comprising a subtraction circuit (7) for determining the difference between the angle and the angle stored in the register (6).