JPH0338969A - Changed point detecting circuit - Google Patents

Abstract

PURPOSE:To execute the detection of a changed point in bit boundary processing only with simple initial set to a shift number accumulator at high speed samely as the detection by word boundary processing by accumulating the outputs of combinational logic and applying the number of bits to be shifted to a barrel shifter. CONSTITUTION:Barrel shifters 102a and 102b are provided to shift input data by the prescribed number of bits and inversional logic is provided to invert the outputs of the barrel shifters 102a and 102b corresponding to color under processing. The combinational logic is provided to detect the bit position of the least significant changed point in the output of the inversional logic and a shift number accumulator 107, which can be initially set to an arbitrary value, is provided to accumulate a shift number to be outputted by the combinational logic and to apply the number of bits to be shifted to the barrel shifters 102a and 102b. Then, before the detection of the changed point, the shift number accumulator 107 is initially set to the desired number of bits. Thus, the changed point is detected from the arbitrary bit position of the input data and time is shortened for detecting the changed point in the bit boundary processing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a change point detection circuit, and particularly to a change point detection circuit that detects a change point within an arbitrary bit boundary in input data.

[Conventional technology]

In recent years, with the advancement of information technology in society, information can be transmitted faster and faster.
There is a growing need to transmit data in larger quantities. Under these circumstances, in the field of facsimile that transmits binary images, MH is used as a method for compressing and encoding images, and conversely expanding and decoding codes, in order to transmit images efficiently.

MR and MMR encoding methods are defined by international standards.

When encoding or decoding an image using these encoding methods, it is necessary to know the position of the point (change point) where the image color changes from white to black or from black to white on each scanning line. This is necessary. Conventionally, a change point detection circuit shown in FIG. 7 has been used for this purpose.

A conventional change point detection circuit uses an input register 7011 that latches input data, and an XOR logic 702 that takes the exclusive OR of adjacent bits in the data of the input register 701,
Mask logic 703, mask logic 7 that masks bits of a specified bit width from the LSB side of the output of R702 to 0
A latch 704 that stores and holds the output of 03, a latch 704
During output, a priority logic circuit 705 outputs the first bit position of 1 on the LSB side, and a shift number accumulator 706 accumulates the output of the priority logic circuit 705.
It consists of

Next, the operation of the conventional change point detection circuit will be explained.

An example of input data to be subjected to change point detection is shown in FIG. 4. In FIG. 4, 0 represents white (W) and 1 represents black (B). Also, W6 means 6 consecutive bits of white, B
4 represents four consecutive bits of black. FIG. 8 shows how a change point in this input data is detected by a conventional change point detection circuit.

Here, the time required for the shift number accumulator to perform one accumulation is called one cycle. The shift number accumulator is reset to zero prior to processing. In cycle l, input register 701 latches the first data. The values of the input register 701 are exclusive-ORed by the XOR logic 702 and are added to the shift number accumulator 7 by the mask logic 703.
After being masked by the number of shifts indicated by 06, the latch 704
is memorized. The priority logic circuit 705 searches the bit position where l is set in the output of the latch 704 from the LSB side, detects l at the 6th bit, and outputs the change point position 6. In response to this, the shift number accumulator 706 adds 6 to the accumulated value, outputs the 6th bit change point, and sets the mask bit number of the mask logic 703 to 6. Next, the priority logic circuit 705 determines the change point position l.
Detects and outputs O. Similar processing is performed thereafter (FIG. 8).

Incidentally, recently there has been a growing need to process data within arbitrary bit boundaries in input data. This is called bit boundary processing. On the other hand, conventional processing in units of multiple bits (words) is called word boundary processing. Bit boundary processing, when considering input data as an image, is a process that allows the boundaries of pixels to be processed to be set in units of one pixel, rather than in units of specific multiple pixels as in the past. . Bit boundary processing allows more detailed processing than word boundary processing.

In the conventional change point detection circuit, in order to perform bit boundary processing, it is necessary to perform post-processing as shown in FIG. 9 on the result of change point detection.

In FIG. 9, the number of bits on which bit boundary processing is performed is defined as bt. First, when the change point position is smaller than bt, that change point is discarded and the next change point is searched. If the change point is greater than or equal to bt, bt is subtracted from the change point.

Next, if the color of the first change point equal to or greater than bt is black, a white change point O is output.

Output the finally determined change point. For example, when detecting the change point of the input data shown in Figure 4 using the 7th bit of the input data as the starting position (b t), the change point of the 6th bit is marked as a black mark, and the next change point is marked as a black mark. Therefore, the change point position is corrected by outputting white 0 and subtracting 7 for the subsequent change points.

[Problem to be solved by the invention]

However, the conventional change point detection circuit requires subtraction processing in bit boundary processing. If this process is performed using software, it will take a long time. On the other hand, if this processing is performed in hardware, a subtracter will be required. Furthermore, at this time, the processing time required for subtraction is twice that of word boundary processing. As described above, if bit boundary processing is performed using the conventional method, there are problems in terms of circuit scale and processing time.

In the past, when the time required for code transmission, encoding, and other parts of decoding was longer than the time required to detect a change point, the time it took to detect a change point was not much of a problem. . But the transmission.

As the time required for encoding and decoding becomes faster due to advances in technology, and as the amount of image data handled increases due to higher resolution scanning, it takes time to detect changing points in bit boundary processing. This has become a problem.

[Means to solve the problem]

The change point detection circuit of the present invention includes a barrel shifter that shifts input data by a predetermined number of hits, and a barrel shifter that shifts input data by a predetermined number of hits, and
an inversion logic that inverts the output of the barrel shifter; a combinational logic that detects the bit position of the lowest change point in the output of the inversion logic; and a shift output of the combinational logic that can be initialized to an arbitrary value. a shift number accumulator that accumulates a number and provides a number of bits to shift to the barrel shifter, and initializes the shift number accumulator to a desired number of bits prior to detecting a change point; Detects a change point from an arbitrary bit position of input data.

[Example 1] Next, an example of the present invention will be described with reference to the drawings.

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

The change point detection circuit of the first embodiment is an input register) 10
1. Barrel shifter 102, OR logic 103, latch 1
04, a color reference register 105, a priority logic circuit 106, and a shift number accumulator 107.

A diagram illustrating the truth table of barrel shifters 102a, b and OR logic 103 is shown in FIG.

Priority logic circuit 106 is comprised of inverting logic 106a and combinational logic 106b. Figure 3(a) shows the basic circuit and truth table of the priority logic circuit.
Shown in b). FIG. 4 shows input data on which change point detection is performed using the configuration of the first embodiment. here,
Assume that the number of bits to perform bit boundary processing is 7.

Next, the operation will be explained.

5 shows how the input data shown in FIG. 4 is processed. The input shift number accumulator 107 is initialized in advance to the number of bits 7 for performing bit boundary processing. The first two words of the input signal are input registers l-10 with l word length.
1a and 1b are latched one after another. The latched input signal is shifted by barrel shifters 102a,b)!
After being shifted by the value indicated by the accumulator 107, the logical sum 10
3 into one word and then latched into the latch 104. The color register 105 is reset to white, ie O, before the change point detection process.

Next, the priority logic circuit 106 inputs the values of the latch 104 and the color register 105, and outputs the bit position of the first different color point on the LSB side. In the example in Figure 4, LS
Since the colors are already different in E, the priority logic circuit 106 outputs 0. The shift number accumulator 107 accumulates the change point positions from the priority logic circuit 106 and outputs the change point if there is a change point.
Reverse the contents of . Change points are detected in the same manner as below (
Figure 5).

[Embodiment 2] FIG. 6 is a block diagram showing a second embodiment of the present invention.

The second embodiment is an example in which the input section of the present invention is configured with two sets of input resists, two sets of multiplexers, and a barrel shifter that takes out one word from two words.

In the second embodiment, input registers 101a, b, multiplexers 602a, b, barrel shifter 603, latch 10
4. Color register 105, FIG. 3(a).

It is comprised of a priority logic circuit 106 and a shift number accumulator 107, as shown in the figure showing the configuration and truth table in FIG.

The operation of the second embodiment is similar to that of the first embodiment.

〔Effect of the invention〕

As explained above, the changing point detection circuit of the present invention can detect changing points in bit boundary processing as quickly as in word boundary processing with only simple initial settings for the shift number accumulator. I can do it. Furthermore, since no subtracter is required, the circuit configuration is simplified.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention, and FIG. 2 shows barrel shifters 102a, b and O in the first embodiment.
Diagrams showing the truth table of R logic 103, Figure 3 (a), (b
) is the priority logic circuit 10 in the first embodiment.
6 is a block diagram showing a truth table, FIG. 4 is a diagram showing an example of input data that is subject to change point detection, and FIG. FIG. 6 is a diagram showing the operation when detecting a change point in the middle of the second embodiment of the present invention.
7 is a block diagram showing a conventional example, FIG. 8 is a diagram showing an example of detecting a change point in the input data shown in FIG. 4 using the conventional example, and FIG. 9 is a block diagram showing an example of the conventional example. 1 is a flowchart showing post-processing required when bit boundary processing is performed using a conventional configuration. 101a, b... Input register, 102a. b...Barrel shifter, 103...R
○Logic, 104...Latch, 105...
- Color resist, 106...Priority logic circuit, 106a...Inversion logic, 106b...
... Combinational logic, 107... Shift number accumulator, 602a, b... Multiplexer, 603.
... Barrel shifter, 701 ... Input register register, 702 ... XOR logic, 703 ...
... Mask logic, 704 ... Latch, 705
...Priority logic circuit, 706...
...Shift number accumulator.

Claims (1)

[Claims] In a change point detection circuit that detects the bit position of a change point, which is a point where a bit in input data changes from 0 to 1 or from 1 to 0, there is a barrel shifter that shifts input data by a predetermined number of bits, and a barrel shifter that shifts input data by a predetermined number of bits. an inverting logic that inverts the output of the barrel shifter according to the color of the barrel shifter; and a combinational logic that detects the bit position of the lowest change point in the output of the inverting logic; and a shift number accumulator that accumulates the output of the logic and provides the number of bits to be shifted to the barrel shifter.