JPH0696217A - Luminance conversion circuit - Google Patents

Abstract

PURPOSE:To process pixel data at a high speed. CONSTITUTION:This circuit is provided with an image memory 3 for storing respective pixel data, histogram preparing circuit 2 for preparing the histogram of luminance-to-frequency from the respective pixel data, histogram storage memory 4 for storing the histogram prepared by this histogram preparing circuit 2, luminance allocating circuit 5 for allocating the luminance order of the respective pixel data stored in the image memory 3 corresponding to the histogram stored in this histogram storage memory 4, and luminance conversion table 6 for converting the luminance order of respective pixel data allocated by this luminance allocating circuit 5 to the pixel data of new luminance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brightness conversion circuit used in an image recognition device or the like.

[0002]

2. Description of the Related Art In an image recognition device, each dot of an image to be recognized (target image) is converted into multivalued digital pixel data (pixel data of luminance), and this pixel data is converted into another by a luminance conversion circuit. It is converted into pixel data of a new brightness with a scale.

For example, in an image recognition apparatus for determining the authenticity of a coin by image processing, a series of pixel data is obtained by reading an image of a coin, and this series of pixel data is added to a new scale having a different scale by a brightness conversion circuit. The pixel data of luminance, that is, pixel data indicating the contrast of coins is converted and then compared with the reference data to determine the authenticity of coins. In this case, the brightness of each dot of the coin changes depending on the conditions at that time, dirt on the coin, etc., so by converting the image signal obtained by reading the coin into pixel data indicating the contrast of the coin by the brightness conversion circuit, Coins are accurately verified without being affected by conditions or the dirt of coins.

Conventionally, the brightness conversion circuit generally stores each pixel data of a target image in a frame memory and processes the content of the frame memory according to a program by a microcomputer (CPU).

[0005]

In the above luminance conversion circuit, since the contents of the frame memory are processed by the CPU according to the program, the overhead time of the program footage of the CPU becomes large, and high-speed conversion of pixel data cannot be performed. It is unsuitable for an image recognition device that intends to process a large amount of pixel data in time.

An object of the present invention is to provide a brightness conversion circuit which can improve the above-mentioned drawbacks and can perform high-speed processing of pixel data.

[0007]

In order to achieve the above object, the invention according to claim 1 is an image memory for storing each pixel data, and a histogram creating circuit for creating a histogram of luminance versus frequency from each pixel data. A histogram storage memory for storing the histogram created by the histogram creation circuit; a brightness allocation circuit for assigning the brightness rank of each pixel data stored in the image memory by the histogram stored in the histogram storage memory; And a brightness conversion table for converting the brightness rank of each pixel data allocated by the allocation circuit into pixel data of a new brightness.

[0008]

Each pixel data is stored in the image memory, the histogram creating circuit creates a histogram of luminance versus frequency from each pixel data, and the histogram is stored in the histogram storage memory. The brightness allocation circuit allocates the brightness rank of each pixel data stored in the image memory by the histogram stored in the histogram storage memory, and this brightness rank is converted into pixel data of new brightness by the brightness conversion table.

[0009]

FIG. 1 shows an embodiment of the present invention. The brightness conversion circuit 1 of this embodiment is composed of hardware composed of individual parts without intervention of a program, and realizes high-speed processing of pixel data. Specifically, the brightness conversion circuit 1 is composed of a histogram creation circuit 2, an image memory 3, a work memory 4, a brightness allocation circuit 5, a brightness conversion table 6 and an address generation counter 7, and a histogram creation circuit 2 and a brightness allocation circuit 5 Is a hardware logic circuit including an adder and the like. RAM is used for the image memory 3 and the work memory 4, and the brightness conversion table 6 is configured by ROM (or RAM).

Further, the frame memory 8 stores a series of pixel data to be subjected to luminance conversion processing, that is, each dot of an image (target image) to be recognized by the image recognition device, into multivalued digital pixel data (pixels of luminance). The converted data is stored. This frame memory 8 displays the target image as C
A / A that converts a series of analog pixel data obtained by reading with an image sensor consisting of a CD into multi-valued digital pixel data
A D converter may be used. The controller 9 stores a series of pixel data to be subjected to the brightness conversion processing in the frame memory 8
Alternatively, it is a circuit for inputting from the A / D converter to the histogram creation circuit 2 and the image memory 3 in the brightness conversion circuit 1, and DMA when the frame memory 8 is used.
A controller is used and A is used instead of the frame memory 8.
A CPU is used when the / D converter is used.

In the brightness conversion circuit 1, multivalued digital pixel data is input to the histogram creation circuit 2 and the image memory 3 from the frame memory 8 or the A / D converter in synchronization with the system clock from the clock generator 10. The clock generator 1 processes the multi-valued digital pixel data.
It is performed in synchronization with the system clock from 0.

FIG. 2 shows an operation flow of the brightness conversion circuit 1. A series of pixel data to be subjected to the brightness conversion processing is sequentially synchronized with the system clock from the clock generator 10 by the controller 9 so that the pixel data is sequentially transferred from the frame memory 8 or the A / D converter to the histogram in the brightness conversion circuit 1. When input to the creating circuit 2 and the image memory 3, the series of pixel data is stored in the image memory 3, and at the same time, the histogram creating circuit 2 stores the series of pixel data in the work memory 4 as shown in FIG. Create a histogram of luminance versus frequency.

When the input of a series of pixel data is completed, the brightness allocating circuit 5 determines the brightness from the highest (or the lowest) based on the histogram in the work memory 4.
The ranking is performed, and the luminance and the ranking are written in the work memory 4 so as to have the relationship between the address and the data of the work memory 4 as shown in FIG. For example, the brightness allocation circuit 5
Since the luminance rank of 100 is the 50th, the data of the rank 50 is written to the address 100 of the work memory 4, and the luminance of 099 is the 53rd rank, so the address of 099 of the work memory 4 is ranked. Data 53 is written, and since the brightness ranking 098 is 60th, the data 60 is written to the address 098 in the work memory 4.

After the luminance allocating circuit 5 ranks all the luminances and writes them in the work memory 4, the counter 7 is activated to read a series of pixel data from the image memory 3 sequentially from the beginning. Is used as an address to access the work memory 4 to extract the data of the luminance rank corresponding to the pixel data. The brightness conversion table 6 is accessed by this brightness rank data, and pixel data of new brightness having another scale corresponding to the brightness rank data is output as the pixel data after the brightness conversion.

Here, in the brightness conversion table 6, as shown in FIG. 5, the relationship between the brightness rank data and the pixel data of the new brightness having another scale is stored as the relationship between the memory address and the memory data. . The pixel data of the new luminance is, for example, 200 in the 50th luminance rank, 202 in the 51st luminance rank, 202 in the 52nd luminance rank, and 203 in the 53rd luminance rank. Therefore,
Original pixel data having a brightness of 100 will be converted into new pixel data having a brightness of 200, and similarly, original pixel data having a brightness of 099 is new pixel data having a brightness of 210. Will be converted to.

In this way, all pixel data in the image memory 3 are converted into new pixel data. In this embodiment, since the hardware is configured so that the program does not intervene, the overhead time becomes zero and the pixel data processing can be speeded up. When a CPU is used as the controller 9, the CPU need only input a series of pixel data to the brightness conversion circuit 1. Further, when a DMA controller is used as the controller 9, higher speed pixel data processing can be realized.

By the way, in the above embodiment, the histogram creating circuit 2, the image memory 3, the work memory 4, the brightness allocating circuit 5, the counter 7 and the controller 9 are constituted by a gate array, and the brightness conversion table 6 is an EPROM and the frame memory. If 8 is used, the frame memory 8
When pixel data of 514 × 22 dots is cut out and input to the brightness conversion circuit 1, the brightness conversion of the pixel data is about 3 to 4 msec, which is 100 times faster than a brightness conversion circuit using a conventional CPU. I was able to measure it.

[0018]

As described above, according to the invention described in claim 1, an image memory for storing each pixel data, a histogram creating circuit for creating a histogram of luminance versus frequency from each pixel data, and this histogram creating A histogram storage memory that stores the histogram created by the circuit,
A luminance allocating circuit for allocating the luminance rank of each pixel data stored in the image memory by the histogram stored in the histogram storage memory, and a luminance rank of each pixel data allocated by the luminance allocating circuit for a pixel of a new luminance. Since the brightness conversion table for converting into data is provided, the program can be configured by hardware without intervention, the overhead time can be set to zero, and high-speed processing of pixel data can be performed.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing an operation flow of the same embodiment.

FIG. 3 is a diagram showing an example of a histogram of the same embodiment.

FIG. 4 is a diagram showing an example of luminance rank data in a work memory in the embodiment.

FIG. 5 is a diagram showing an example of data in a luminance conversion table in the same embodiment.

[Explanation of symbols]

 2 Histogram creation circuit 3 Image memory 4 Work memory 5 Luminance allocation circuit 6 Luminance conversion table

Claims (1)

[Claims] 1. An image memory for storing each pixel data, a histogram creation circuit for creating a histogram of luminance vs. frequency from each pixel data, a histogram storage memory for storing the histogram created by this histogram creation circuit, A brightness allocation circuit that allocates the brightness rank of each pixel data stored in the image memory by the histogram stored in the histogram storage memory, and the brightness rank of each pixel data allocated by this brightness allocation circuit to the pixel data of the new brightness. And a brightness conversion table for converting the brightness into a brightness conversion circuit.