JPH0652307A - Device and method for extracting edge from digital image signal - Google Patents

Abstract

PURPOSE:To accurately extract edge information in a digital image with a simple hardware or processing. CONSTITUTION:An input digital video signal is divided into small blocks by a block circuit 2. The maximum value and minimum value of each block are detected by a maximum value detection circuit 3 and minimum value detection circuit 4 and as the difference of these values, a dynamic range DR is calculated from a subtraction circuit 5. The dynamic range DR is supplied to a comparator circuit 6 and in the case of the block of Th1>DR, it is judged no edge information is contained, Normalized pixel data PD are quantized by a ROM 8 adaptively to the dynamic range DR. Quantized data Q are compared with a threshold value Th2 by a comparator circuit 10. The picture element in the block containing the edge information is converted to either of '0' and '1' by the threshold value Th2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge extracting apparatus and method for extracting edge information from a digital image signal.

[0002]

2. Description of the Related Art Extracting edge information from a digital image signal has various fields of use in digital image processing such as position detection of chip parts during automatic mounting in a manufacturing process. Conventionally, a differential filter or a Laplacian filter is used, and a place where the level change of the digital video signal is drastic is detected as an edge.

[0003]

However, when the above-mentioned filter is constructed by a digital circuit, a digital multiplier is generally required, and there is a problem that the scale of hardware becomes large. Further, when the level change is not relatively large, there is a problem that edge extraction cannot be performed.

Further, the applicant of the present application first subdivides the digital image into blocks, and when the difference between the maximum value and the minimum value of each block is larger than a certain threshold value, it is determined that the block contains edge information. We have proposed an edge extraction device that estimates and sets the values of all pixels in the block to, for example, the white level. This can solve the problem when using the above-mentioned digital filter, but it is necessary to set the threshold appropriately according to the average brightness of the entire screen affected by the illumination at the time of shooting, Further, the whole block shows edge information, and the accuracy is insufficient.

Therefore, the object of the present invention is to provide an edge extracting apparatus and method which can be realized by a simple hardware or software process which does not use a multiplier and which can extract edges even when the level change is not large. Especially.

Another object of the present invention is to provide an edge extraction apparatus and method capable of preventing the edge extraction accuracy from varying due to the difference in average screen brightness.

Still another object of the present invention is to provide an edge extraction device and method capable of extracting edge information with pixel-by-pixel accuracy.

[0008]

SUMMARY OF THE INVENTION According to the present invention, an input digital video signal is subdivided into block-unit data consisting of a plurality of pixel data, and the maximum value, the minimum value, the maximum value and the minimum value of the plurality of pixel data are divided for each block. A circuit that detects a dynamic range that is a difference between values, a first comparison circuit that compares the dynamic range with a first threshold value, a circuit that normalizes pixel data with a maximum value or a minimum value, Of the block that has a dynamic range smaller than the first threshold, and a second comparator that compares the output of the quantization circuit with a second threshold value. For blocks in which the pixel data are all the first value and the dynamic range is larger than the first threshold value, the second threshold value is used to set the pixel data to the first value and An edge extraction device from the digital image signal comprising a circuit for converting one of the second value.

[0009]

The brightness difference exists in the block containing the edge information. When this brightness difference is larger than the first threshold value, it is determined that the block has edge information. Normalization for removing the minimum value of the block is performed from the pixel data, and the normalized data is quantized. In the quantized data of the block including the edge information, the pixel data is converted into the first value or the second value using the second threshold value.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 is an input terminal to which a digital video signal is supplied. In this digital video signal, one pixel is 8-bit data. The input digital video signal is converted by the blocking circuit 2 from raster scan order to block order. The block has a size of (n pixels × m lines), for example, (6 × 6)
Is the size of. The block size is appropriately selected in consideration of the usage field of the extracted edge information.
The blocking circuit 2 includes an m-line memory.

A maximum value detection circuit 3, a minimum value detection circuit 4 and a delay circuit 5 are connected to the blocking circuit 2. The maximum value detection circuit 3 detects the maximum value MAX for each block, and the minimum value detection circuit 4 detects the minimum value MI for each block.
Detect N. The minimum value MIN is subtracted from the maximum value MAX by the subtraction circuit 6, and the subtraction circuit 6 obtains the dynamic range DR of the block. This dynamic range DR is supplied to the ROM 8 and the comparison circuit 9. R
The pixel data PD obtained by subtracting the minimum value MIN from the subtraction circuit 7 is supplied to the OM 8.

By subtracting the minimum value, the ROM 8 adapts the normalized pixel data PD to the dynamic range DR and quantizes it, and outputs each pixel as data Q having a predetermined number of bits. You may perform the normalization which subtracts pixel data from the maximum value MAX. In the example of 4-bit quantization, as shown in FIG. 2, the quantization step is calculated by dividing the dynamic range DR of the block by 2 ⁴ = 16, and the value of the data PD from the subtraction circuit 7 is calculated. 0-15 by dividing by the quantization step
A quantized output Q is generated. The ROM 8 stores a table for performing this quantization processing. Since it is normalized, the influence of the average brightness of the input digital video signal can be removed, and the fixed threshold value enables highly accurate edge extraction.

In the comparison circuit 9, the dynamic range DR
Is compared with a certain threshold Th1. The comparison circuit 9 is T
When h1> DR, an output of “0” is generated, and Th1 ≦ D
When R, an output of "1" is generated. The output signal of the comparison circuit 9 enables / disables the comparison circuit 10. As an example, the output signal of the comparison circuit 9 is supplied to the comparison circuit 10 as its clear signal.
In the clear state, the output signal of the comparator circuit 10 is "0" regardless of the input signal. The dynamic range DR for the block including the edge is large and the dynamic range D for the block not including the edge is large.
R is small. Therefore, when the dynamic range DR is less than or equal to the threshold Th1, the values of all the pixels in the block are replaced with "0".

The dynamic range DR is the threshold Th1.
For blocks that are larger than R,
A comparison output of the output data (that is, the quantized data) Q of the OM8 and the threshold value Th2 is generated. When Th2> Q, a comparison output of “0” is generated, and when Th2 ≦ Q, a comparison output of “1” is generated.

The output signal of the comparison circuit 10 is supplied to the block decomposition circuit 11 and converted from the block order to the raster scan order. The memory required for the block decomposition circuit 11 is for m lines. Output data obtained by converting each pixel data into a value of "0" or "1" is obtained at the output terminal 12 of the block decomposition circuit 11. "1" of this output data is data corresponding to the edge information, as can be understood from the above-mentioned processing.

As shown in FIG. 3, a background 21 is displayed in one screen.
Consider an input image in which a triangular object 22 having a brightness different from that of the background 21 exists. In this case, since the block in the background 21 does not have edge information, its dynamic range DR is smaller than the threshold Th1 and all the pixels in that block are set to “0”, for example, the black level. The block inside the object 22 also has no edge information, and thus is set to the black level. In the block including the edge information, the pixels having the threshold value Th2 or more are set to "1", for example, the white level.

As shown in the enlarged view of FIG. 3, the edge of the object 22 is from the level L1 of the background 21 to the level L of the object 22.
Stand up with a slope at 2. This tilt exists both horizontally and vertically. Therefore, Th1 ≦
Even in the DR block, there is a pixel smaller than the threshold Th2, and this is a black level. As a result, an output image in which only the edge portion 23 is white and the background 21 and the in-object region 24 are black can be obtained. More specifically, even in a block including edge information, among a plurality of pixels that generate a sloping level, a pixel having a value larger than a threshold value Th2 is converted into a value “1”. In this case, the value of a pixel smaller than the threshold Th2 may be converted into "1".

FIG. 4 shows another embodiment of the present invention. Similar to the above-described embodiment, the dynamic range DR is detected for each block, the dynamic range DR is compared with the threshold value Th1 in the comparison circuit 9, and the pixel data is quantized in the ROM 8 in accordance with the dynamic range DR. , The comparison circuit 10 which is cleared by the output of the comparison circuit 9
At, the quantized output and the threshold Th2 are compared.

In the embodiment of FIG. 4, the comparison circuits 13 and A
An ND gate 14 is further provided. The comparison circuit 13
It is cleared by the output of the comparison circuit 9, and the ROM 8
The quantized data Q from (3) and the threshold value Th3 are compared.
The relationship is set to Th3> Th2. The outputs of the comparison circuits 10 and 13 are supplied to the AND gate 14, and the output of the AND gate 14 is supplied to the block decomposition circuit 11.
The output of the AND gate 14 becomes "1" only when the two comparison outputs simultaneously become "1".

The comparison circuit 13 is such that when Th3 ≧ Q,
An output of "1" is generated, and when Th3 <Q, an output of "0" is generated. Therefore, the comparison circuits 10, 13 and AN
The D-gate 14 operates as a window comparator that produces an output of "1" when the quantized data exists between Th2 and Th3.

In the embodiment of FIG. 4, as shown in FIG. 5, from the input image composed of the background 21 and the object 22, the output image in which the background 21 and the in-object region 24 are black and the edge portion 23 is white. Can be generated. Since the edge has the level gradient as described above, as shown in an enlarged view in FIG. 5, pixels along the edge can be white in the block including the edge information. Therefore, the resolution of edge extraction can be increased as compared with the embodiment of FIG.

The output of the comparison circuit 9 for discriminating the block containing the edge information and the block not containing the edge information may not be used as the clear output of the comparison circuit 8 as shown in FIG. That is, as shown in FIG. 6, the comparison outputs of the comparison circuits 9 and 10 may be supplied to the AND gate 15.

FIG. 7 shows still another embodiment of the present invention. Similar to the above, one image is subdivided into blocks, the dynamic range DR of each block is detected, and pixel data in which the minimum value MIN is subtracted is formed. Here, the dynamic range DR and the normalized pixel data PD are supplied to the ROM 16, and the ROM 16 sets pixels having edge information to “1” and other pixels to “0”.

The conversion table shown in FIG. 8 is stored in the ROM 16. The horizontal axis in Fig. 8 is the dynamic range D
R, whose vertical axis is the value of the normalized data PD. When each pixel of the input data has 8 bits, the horizontal axis and the vertical axis have values of 0 to 255. The portion above the diagonal line 17 extending from the position where the data PD and DR of this table are both 0 to the upper right corner may be irrelevant (don't care). Further, the threshold value Th1 is set on the horizontal axis, a vertical line 18 is drawn from this, and the threshold values Th2 and Th3 are set on the vertical axis, and these threshold values and PD and DR are both 0. Draw lines 19 and 20 that connect the position and.

Then, the output data in the area on the lower side of the diagonal line 17 which is a low value on the left side of the line 18 is set to "0". In the high value area on the right side of the line 18, the output data of the area sandwiched between the lines 17 and 19 is set to "0". In the area on the right side of the line 18, the output data of the area sandwiched by the lines 19 and 20 is set to "1". In the area on the right side of the line 18, the output data of the area below the line 20 is set to "0". In this way, the conversion table in which the output data is set is stored in the ROM 16. With this conversion table, output data which becomes "1" corresponding to an edge can be obtained only by supplying the dynamic range DR and the normalized data PD to the ROM 16 as an address.

Also in the configuration using the threshold values Th1 and Th2 shown in FIG. 1, the comparison circuit can be omitted by constructing the conversion table of the ROM as described above. Furthermore, FIG.
In the above configuration, the ROM 8, the comparison circuit 9, and the comparison circuit 10 in FIG. 6 are replaced with one conversion table, but these two may be replaced with the conversion table.

Since the present invention can be processed at extremely high speed even in software processing of a computer, it can be realized in real time even in a general-purpose image processing apparatus using a computer. FIG. 9 is a flowchart of an example of software processing.

The input image data is divided into blocks in step 31. Next, the dynamic range DR and the minimum value MI
N is detected, and the pixel data is quantized according to the dynamic range DR (encoding processing in step 32). Then, the decision steps 33, 34 and 35 are carried out in order. Step 33 determines whether DR <Th1 holds. Step 34 determines whether Q <Th2 holds. Step 35 determines whether Q> Th3 holds.

If the result of these determination steps 33, 34 or 35 is affirmative, the control moves to step 36 and the quantized data Q is converted to "0" (for example, black level). When the results of steps 33, 34 and 35 are all negative, the quantized data Q is converted to "1" (for example, white level) in step 37. Block decomposition processing is performed in step 38 after these steps 36 and 37, and the data is output in the order of raster scanning.

Contrary to this embodiment, the value of the pixel corresponding to the extracted edge may be set to "0" and the value of the other pixels may be set to "1". Further, the "0" and "1" pixels may be converted into distinguishable brightness or colors other than the black and white levels.

[0031]

The present invention does not require a digital multiplier, as compared with an edge extraction device using a digital differential filter, and therefore can be realized with a small scale of hardware and a small number of steps of software. There is an advantage that it is possible to extract an edge having a small difference in brightness. According to the present invention, a process of discriminating a block containing edge information and a block not containing it, and a process of discriminating a pixel containing an edge information into a pixel of an edge portion and a pixel other than that are performed. Can be extracted. Further, since the pixel data is normalized with the minimum value or the maximum value, the edge information can be extracted accurately without being affected by the average brightness in the block.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining quantization in one embodiment of the present invention.

FIG. 3 is a schematic diagram for explaining data conversion according to an embodiment of the present invention.

FIG. 4 is a block diagram showing the configuration of another embodiment of the present invention.

FIG. 5 is a schematic diagram for explaining another embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of still another embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of still another embodiment of the present invention.

FIG. 8 is a schematic diagram for explaining still another embodiment of the present invention.

FIG. 9 is a flowchart for explaining the present invention which is performed by software processing.

[Explanation of symbols]

 3 Maximum value detection circuit 4 Minimum value detection circuit 6, 7 Subtraction circuit 8 Encoding ROM 9, 10 Comparison circuit

Claims (8)

[Claims] 1. An input digital video signal is subdivided into block-unit data consisting of a plurality of pixel data, and the difference between the maximum value and the minimum value and the maximum value and the minimum value of the plurality of pixel data is divided for each block. Means for detecting a dynamic range, first comparing means for comparing the dynamic range with a first threshold value, means for normalizing the pixel data with the maximum value or the minimum value, and the normalization A means for quantizing the generated data in accordance with the dynamic range, and a second means for comparing the output of the quantizing means with a second threshold value.
And the dynamic range is smaller than the first threshold, the pixel data of the block are all first values,
Means for converting the pixel data into one of the first value and the second value using the second threshold value for the block whose dynamic range is greater than the first threshold value; Edge extraction device from digital image signals. 2. An input digital video signal is subdivided into block-unit data consisting of a plurality of pixel data, and the difference between the maximum value and the minimum value and the maximum value and the minimum value of the plurality of pixel data is divided for each block. Means for detecting a dynamic range, first comparing means for comparing the dynamic range with a first threshold value, means for normalizing the pixel data with the maximum value or the minimum value, and the normalization A means for quantizing the generated data in accordance with the dynamic range, and a second means for comparing the output of the quantizing means with a second threshold value.
Comparing means for comparing the output of the quantizing means with a third threshold value larger than the second threshold value, and the dynamic range is smaller than the first threshold value. All the pixel data of the block is the first value,
For the blocks whose dynamic range is greater than the first threshold, convert the pixel data less than the second threshold or greater than the third threshold to the first value. An edge extraction device from a digital image signal, which further comprises means for converting the pixel data which is larger than the second threshold value and smaller than the third threshold value into a second value. 3. The edge extraction device according to claim 1, wherein the output of the first comparing means and the output of the second comparing means are supplied to a logic gate, and a converted output is obtained from the logic gate. An edge extraction device characterized by the above. 4. The edge extraction device according to claim 1, wherein at least one of the first comparison means and the second comparison means, the quantization means, and the conversion means are configured by a conversion table. An edge extraction device. 5. The edge extracting apparatus according to claim 2, wherein at least two of the first comparing means, the second comparing means and the second comparing means, the quantizing means, and the converting means. An edge extraction device characterized by comprising a conversion table. 6. The edge extraction device according to claim 1 or 2, wherein the means for comparing the output of the quantizing means with the second threshold value has the dynamic range as the first threshold value. An edge extraction device characterized by being enabled / disabled by the output of the comparing means. 7. A step of subdividing an input digital video signal into block-unit data consisting of a plurality of pixel data, the maximum value, the minimum value, the maximum value and the minimum value of the plurality of pixel data for each block. Detecting a dynamic range that is a difference between the pixel data and the pixel data, normalizing the pixel data with the maximum value or the minimum value, and quantizing the normalized data according to the dynamic range; A first determining step for checking that the output of the quantizing means is less than a second threshold; a first determining step for checking that the output of the quantizing means is less than a second threshold; A step of setting the pixel data to a first value when any of the second determination steps has a positive result, and the first determination step And when the second determination step are both negative result, the edge extraction method from a digital image signal comprising the step of the pixel data and the second value. 8. A step of subdividing an input digital video signal into block-unit data consisting of a plurality of pixel data, the maximum value, the minimum value, the maximum value and the minimum value of the plurality of pixel data for each block. Detecting a dynamic range that is a difference between the pixel data and the pixel data, normalizing the pixel data with the maximum value or the minimum value, and quantizing the normalized data according to the dynamic range; A first determining step for checking that the output of the quantizing means is smaller than a second threshold; and a second determining step for checking that the output of the quantizing means is smaller than the second threshold. A third determining step for checking that the threshold value is greater than a threshold value of 3, and the first determining step, the second determining step and the third determining step. When any one of the determining steps has a positive result, the step of setting the pixel data to the first value, the first determining step, the second determining step and the third determining step are all negative results. And a step of setting the pixel data to a second value, the edge extraction method from the digital image signal.