JPH0345018A - Method and apparatus for compressing digital signal group - Google Patents

Abstract

PURPOSE:To attain efficient compression in a few compression period by making a length of measuring direction of each compression period unequal corresponding to the degree of a change in a value of an original digital signal group whose value changes in one measuring direction. CONSTITUTION:The apparatus is provided with a change degree arithmetic means 12 calculating the degree of the change in the measuring direction of an original digital signal group whose value changes to one measuring direction, and a compression period length decision means 13 obtaining the measuring direction length of the compression period in response to the degree of a change in the picture data obtained by the arithmetic means. Then the change degree arithmetic means 12 obtains the degree of the change of the original digital signal group in the measuring direction, and the compression period length decision means 13 decides the length of the compression period in response to the degree of change. Thus, each compression digital signal is generated based on each compression period where the measuring direction length is made unequal corresponding to the change degree of the value of the original digital signal group and the compression digital signal group with high compression efficiency corresponding to the change in the value of the original digital signal group with excellent response is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a digital signal group compression method that compresses an original digital signal group whose value changes with respect to one measurement direction into a compressed digital signal group with a smaller number of signals. Method and Apparatus
Q.

(Prior Art) In general, in order to convert an arbitrary amount of change into a group of original digital signals whose values change with respect to one measurement direction, and to improve efficiency when further utilizing this group of original digital signals, Compression conversion is performed into a compressed digital signal group in which the tendency of value changes corresponds to the original digital signal group, but the number of signals is smaller than the number of signals in the original digital signal group.

An example of compressing such a digital signal group is when an arbitrary image 1 is printed on paper 3 as a reproduced image 1a, as shown in FIG. 10, for example.

To explain further, FIG. 10 shows a case where the image 1 and the characters 2 shown on the leftmost part are collected together and printed as the reproduced image 1a and the reproduced characters 2a on the paper 3 as shown in the rightmost part. ing. One character 2 is converted into a digital signal by a character data input device 4 such as a keyboard, and is inputted to the host computer 6 as character data. The other image 1 is obtained by an image data input device 5 such as an image scanner.
is read as image data by the host combination 1-
Input to Taro. The image data read from this image 1 is an original digital signal consisting of a set of digital signals obtained by measuring the shading of the image 1 for each unit pixel along the scanning direction of the scanning line. If this original digital signal is used as it is for printing image 1, the amount of information will be too large, and the CPU of the host computer 6 and printer 7 will need to use it.
This places a heavy burden on control devices such as t! It becomes a tetravalent substance.

Therefore, conventionally, a compressed digital signal that changes according to the change in the original digital signal and has a small number of signals has been created, and this compressed digital signal is used to perform the editing process of image 1 and character 2 by the host computer 6. It is supposed to be done.

The print data created by the host computer 6 is sent to the printer 7, and the printer 7 prints the reproduced image 1a and reproduced characters 2a on the paper 3 based on the received print data.

[Problem to be solved by the invention]

However, conventional methods for compressing original digital signals have the following problems.

That is, the reading of the shading of the image 1 by the image data input device 5 is carried out by repeatedly measuring the image 1 shown in FIG. 10 while scanning it in the X direction.

FIG. 11 shows 1iUii image data obtained by scanning the image 1 in the X direction by the image data input device 5 and consisting of the degree of density of the image 1 along the scanning line. This image data is the density rI! measured for each pixel in the X direction of image 1! The four tone values are used as digital signal values, and these digital signal values are displayed as a line graph, which is a type of original digital signal group whose armor changes in the X direction. When compressing this image data,
As shown in FIG. 11, the entire scanning range of image 1 in the X direction is equally divided into a large number of compressed sections of equal width in the X direction, and the original digital signal group divided for each compressed section is divided into one
The signal is compressed into two compressed digital signals.

However, as in the image data shown in FIG. 11, the original digital signal group often includes a high frequency component region whose value changes rapidly and a low frequency component region whose value changes slowly. In order to compress the high frequency component so that it changes responsively in response to the change, the length in the measurement direction, that is, the length in the X direction, of the compression section to be equally divided must be shortened.

However, if the length of the compression section in the X direction is reduced,
This creates more compressed digital signals than necessary in the low frequency component region, resulting in a signal that contains redundant data and poor compression efficiency, which ultimately places a heavy burden on subsequent various control processes in the host computer 6 and printer 7. will be multiplied by . From such a thing,
In the conventional method described above, it is difficult to determine the number of equal divisions of the entire scanning range, that is, the length of the compression section in the measurement direction to an appropriate value.

The present invention has been made in view of these points, and it is an object of the present invention to convert a group of original digital signals whose values change in one measurement direction into a group of compressed digital signals whose values change responsively to the changes. Moreover, it is an object of the present invention to provide a digital signal group compression method and apparatus that can efficiently compress a group of digital signals in a small number of compression sections.

[Means to solve the problem]

In order to achieve the above object, the digital signal group compression method of the present invention compresses an original digital signal group whose value changes with respect to one measurement direction using compression sections divided into a plurality of sections in the 1tll value direction. In a digital signal group compression method, the length of each compression section in the measurement direction is made unequal in accordance with the degree of change in the value of the original digital signal group. Therefore, the digital signal group pressure line device of the present invention includes a change degree calculation means for calculating the change degree of the value in the measurement direction of the ring digital signal group whose value changes with respect to one measurement direction, and The apparatus is characterized in that it has a compression section length determining means for determining the length of the compression section in the measured value direction in accordance with the degree of change in the ring digital signal group obtained by the degree calculation means.

[For production]

According to the present invention, by operating the gi device of the present invention in accordance with the method of the present invention, it is possible to obtain a compressed digital signal group in which a ring digital signal group is efficiently compressed.

That is, the degree of change calculating means calculates the degree of change in the value of the ring digital signal group in the measurement direction, and the compression section length determining means determines the length of the compression section according to this degree of change. As a result, each compressed digital signal is created based on each compression section whose length in the m* direction is made unequal according to the degree of change in the value of the ring digital signal group, and the length is made responsive to changes in the value of the ring digital signal group. Compressed digital signals with good compression efficiency can be obtained.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 9.

In this embodiment, as the ring digital signal group, as shown in FIGS. 1 and 2, image data consisting of the gradation of image 1 is targeted, as in the conventional case.

FIG. 1 schematically shows a digital signal compression means 11 of the present invention.

The digital signal compression means 11 of this embodiment converts image data consisting of the degree of change in the value in the m-line direction of a ring digital signal group whose value changes with respect to one measurement direction, that is, the W4 tone value of the density of the image 1. A change degree calculation means 12 for calculating the degree of change in the X direction, and a compression section for calculating the measured length of the compression section, that is, the length in the X direction, according to the degree of change in the image data obtained by the change degree calculation means 12. It has length determining means 13. Moreover, this compression section length determining means 13
It has a signal compression means 14 which converts an original digital signal into one compressed digital signal according to a predetermined method using the compression interval determined by , and a CPU 15 which operates these means in conjunction with each other.

Next, the operation of this embodiment will be explained.

In this embodiment, as shown in FIG. This converts each signal group into one compressed digital signal.

To explain this operation with reference to the schematic flowchart of FIG. 4, when the compression processing operation is started, first, as shown in step 5T11, the image data input device 5 performs density detection scanning in a certain X direction of the image 1. Then, the image data is read, that is, the ring digital signal group is read. Next, as shown in step 5T12,
Change degree calculation means 12 and compression section length determination means 13
The compression interval is set by That is, the degree of change calculating means 12 calculates the degree of change in the value of the ring digital signal group, and the compression interval length determining means 13 determines the length of the compression interval in accordance with the degree of change.

Next, in step 5T13, the signal compressing means 14 creates a compressed digital signal group using the compression section according to a predetermined method.

Various methods can be used to set the compression interval in step 5112, but for a ring digital signal group including a high frequency component region, such as the image data shown in FIG. It is better to shorten the length of the compression interval for the part and increase the length of the compression interval for the part where the degree of change in value is gradual. Obtainable.

In addition, in order to concretely set the compression intervals in step ST1□, it can be done smoothly and appropriately by determining the interval points that are the start and end points of each compression interval, which are indicated by black circles on the X-axis in Fig. 3. be able to.

Selection of this interval point is preferably carried out by the change degree summation means 12 and the compression interval length determining means 13 according to the flowchart shown in FIG. 5, for example.

That is, in step 5121, a plurality of pixel positions, ie, pixel X coordinates, at locations where the degree of change in value is large in the image data of FIG. 3 are selected as interval point candidates. next,
In step 5122, the plurality of interval point candidate sets selected as described above are narrowed down to a predetermined number of interval point candidates. Next, in step 5123, the interval point candidates narrowed down as described above are narrowed down to those separated by a predetermined minimum number of pixels or more. Next, in step 5124, a number of new interval point candidates corresponding to the number reduced by the narrowing down in step 5T23 is added to obtain the predetermined number of interval point candidates. Next, step 5T2
5, addition of interval points with monotonicity exceeding a predetermined value is performed. In other words, in a monotonous section where the gradation value only increases or decreases as the X coordinate increases,
The start point and end point where the absolute value of the difference in gradation values between the start point and end point of the section is greater than or equal to a predetermined value are added as section point candidates, and a compression section is determined using all these section point candidates as section points. do.

A more specific example of the flowchart in Figure 5 is shown in Figure 6.
2 is a flow chart of the figure.

To further explain this FIG. 6, step 5T31
A plurality of interval point candidates are selected in . This selection is to select a location where the degree of change in image data is large, and as a selection method, it is preferable to select pixels that satisfy the following conditions (1) and (2), for example.

Now, let the gradation value of the pixel data shown in FIG. 3 be a function g(X), and let the gradation of the pixel at position i in the X direction be q,
D""(i+1) '(i) If (i)
(i) If (1) D(,,)-D <0 (i) (2) wax(l D(i-1) l l D
l) >C, where C is a constant (default 1!I) A location that both satisfies the following conditions.

Conditions (1) and (2) mean that the digital signal of the pixel portion whose X coordinate is (i) is transmitted in units of 1i! The degree of change in the signal between the previous and subsequent pixel portions changes positively or negatively by ii elements, and the product of the absolute values of each change exceeds a predetermined number C or more. This is subject to the condition that the

Next, in step 5132, the step 5T3
For each interval point candidate selected in step 1, the following formula % formula %) () is assigned an order starting from the largest calculated value. in this case,
If there is a plurality of interval point candidates with the same calculation distance and it is necessary to select one from among them, for example, they are selected in order from the one with the smallest X coordinate value of the pixel.

Next, in step 5133, a predetermined number (for example, 30) of high-ranking section points are selected from the set of section point candidates.

Next, in step 5T34, it is determined whether or not the interval between the 30 selected section point candidates falls within a predetermined minimum number of pixels as a neighborhood condition. If the section point candidate is located nearby, YES is determined and the process proceeds to step S13.
．． If there is no one nearby, the determination is NO and the process proceeds to step 5138, which will be described later.

Next, in step 5T35, one of the two interval point candidates that are considered to be neighboring points is deleted, and the other is left as an interval point candidate. In this case, assuming that the interval point candidates whose X coordinates are i and j are now close to each other, `` (i-1)・'' (i) ''''' (j-1)
” Compare D(j), keep the larger value, and delete the other.

Next, in step ST, it is determined whether the total number of interval point candidates that have been selected so far is the predetermined number (30 in this embodiment) set in step 5133, and if YES, as will be described later. If the answer is No, the process advances to step s137.

In this step 5T37, the predetermined number (30)
Step 5T
Select and add them in order from the top in the same manner as in Step 32, and return to Step 5T36.

The operations in step 5T36 and ST3□ are repeated until the determination in step 5136 becomes YES.

Next, in step 5138, ll exceeds a predetermined value.
A tonality judgment is made. This judgment can be made even in a monotonous section where the gradation values only increase or decrease, if the difference in the gradation values between the starting point and the ending point is larger than a predetermined value.
The purpose is to compress the original digital signal group even in the monotonous section to obtain a more appropriate compressed digital signal group. Furthermore, to explain FIGS. 7(a) and (b),
The area from X coordinate i to n is a monotonous section in which the gradation value of each coordinate always increases or decreases (in the figure, it only increases), and each wA at the starting point i and ending point n
It is determined whether the absolute value 19(.)'m of the difference between ill values is larger than a predetermined value, for example 50.

If the determination at step 5T38 is NO, the section point selection operation is completed, and if the determination is YES, step 5139
Proceed to.

In this step 5139, the step 5T3
8, the starting point and ending point −Q in a monotone interval
When I is greater than or equal to the absolute value 1a(.)(i) of the tone value difference from 50, the corresponding starting point and ending point are added as section points. As a result, the sum of the section points determined in step 5136 and the section points added in step 5T39 is set as the section point, and the section point selection operation ends.

By determining the interval points in this manner, a compression interval between each interval point is determined, as shown in FIGS. 3 and 7. This compression section is set such that the section length is short in the high frequency component region and long in the low frequency component region, and the absolute value of the tone value difference between the start point and the end point is set to a predetermined value. A monotonous section exceeding 2 is also considered a compressed section.

Thereafter, in step 5T13 shown in FIG. 4, a compressed digital signal No. 13 is obtained using each compression section, and a compressed digital signal group in one scanning direction is obtained as a whole.

By repeating this compression processing operation for all pixels in the y direction, image data for the entire image 1 is created.

The compressed digital signal group obtained in this way is sent to the host computer 6, and the print signal is edited with the character data of the character 2 sent to the host computer 6 through the character data input device 4. The image is subjected to creation processing and printed on paper 3 by printer 7 as reproduced image 1a.

The image quality of this printed reproduced image 1a is of a high quality almost equivalent to that of the original image 1.

This is a compressed signal created by the signal compression means 14 based on a non-uniform compression interval having the interval length determined by the change degree calculating means 12 and the compression interval length determining means 13 of the digital signal compression means 11. This is because the reproduced compressed digital signal, which is a group of digital signals connected so as to change smoothly in the X direction, changes almost in the same way as the original digital signal group consisting of image data. Also,
Compared to the original digital signal group, the compressed digital signal group has a significantly reduced amount of information, that is, the amount of data, so the burden placed on the host computer 6 and printer 7 is reduced, which allows for high-speed data processing. It is also possible to enable processing.

Next, each compressed digital signal group and each compressed digital signal obtained by compressing the same original digital signal group by the method of this embodiment and the conventional method are changed smoothly in the X direction. The connected reproduced compressed digital signal groups will be compared using FIGS. 8 and 9. 8th
The figure shows the results obtained by the method of this embodiment, and FIG. 9 shows the results obtained by the conventional method. The image data to be compressed, shown by solid lines in both figures, consists of 256 pixels (one scale has two pixels), and for each pixel in the entire scanning direction range, the a of image 1 is
The gradation of degrees is expressed in 8-value digital signals.

In the method of this embodiment, as shown in FIG. 8, a total of 49 compression sections (with section points on the (indicated by black or white circles), and the compressed sections are used to create a compressed digital signal. The compression section length needs to be short in the high frequency component region, and if the variation in tone values is very large, the section length may be "O". (When the section length becomes "0", it is assumed that there are overlapped section points on the same -X coordinate (measurement direction).) In this example, as shown in FIG. There are overlapping interval points (points indicated by white circles), and therefore the compression interval is divided into a total of 49 compression intervals. The broken lines in FIG. 8 indicate a group of reproduced compressed digital signals that connect the reproduced compressed digital signals obtained by reproducing each of these compressed digital signals.

In FIG. 8, when the image data (solid line) and the reproduced compressed digital signal (broken line) overlap, the image data that is the original digital signal group is given priority.

In addition, in the conventional method, as shown in FIG. Creating a signal group.

The broken lines in FIG. 9 indicate a reproduced compressed digital signal group that connects the reproduced compressed digital signals obtained by reproducing these compressed digital signal groups.

As can be seen by comparing FIG. 8 and FIG. 9, according to the method of this embodiment, the number of compression sections is reduced to approximately 172, which is the number of compression sections of the conventional method.
Although the original digital signal is compressed with the number of compression sections, the obtained reproduced compressed digital signal group is as good as that of the conventional example with a large number of compression sections,
This corresponds to changes in the values of the original digital signal group with good responsiveness. Therefore, according to this embodiment, the original digital signal group can be compressed extremely efficiently.

In the above embodiment, the compression target is the original digital signal group consisting of the gray level of each pixel of the image 1, but any digital signal group whose value changes in one illll1m direction can be compressed. I can do it.

In addition, as a method for determining the length of the compression section in the measurement direction,
Methods other than those in each of the above embodiments may be adopted.

For example, after step 5T39 in FIG. 6, it is determined whether the length of the section determined up to that point is within a predetermined length, and if the length is longer than the predetermined length, the length of the section is reduced to less than the predetermined length. You may further add interval points for division.

Furthermore, the method and apparatus of the present invention are not limited to the above embodiments, and can be modified in various ways as necessary.

〔Effect of the invention〕

Since the digital signal group compression method and apparatus of the present invention are constructed and operate in this manner, the original digital signal group whose value changes in one of the 11 directions can be compressed into a compressed digital signal group whose value changes in a responsive manner to the change. It can be compressed into a signal group, and can be efficiently compressed using a small number of compression sections, and subsequent signal processing can be performed simply and at high speed.

[Brief explanation of drawings]

1 to 7 show an embodiment of the digital signal group compression method and device of the present invention, FIG. 1 is a block diagram schematically showing the device of the present invention, and FIG. 2 shows the device of the present invention for image processing and FIG. 3 is a block diagram showing the case where the method is used in a printer that reproduces images. FIGS. 4 to 6 are flowcharts showing the state of compression processing according to the method of the present invention, FIG. 7(a) is a diagram similar to FIG. 3 showing a monotonous section, and FIG. 7(b) ) is an enlarged view of the broken line part in FIG. 8th showing
10 and 11 are similar views to FIGS. 2 and 3, respectively, showing the conventional example. 11... Digital signal group pressure line device, 12... Change degree calculating means, 13... Compression section length determining means, 14
...signal compression means, 15...cpu.

Claims (1)

[Claims] 1) A digital signal group compression method in which an original digital signal group whose value changes with respect to one measurement direction is compressed using compression sections divided into a plurality of compression sections in the measurement direction, A digital signal group compression method, characterized in that the lengths of the compression sections in the measurement direction are made unequal in accordance with the degree of change in the values of the original digital signal group. 2) change degree calculation means for calculating the change degree of the value in the measurement direction of the original digital signal group whose value changes with respect to one measurement direction, and the original digital signal obtained by the change degree calculation means A digital signal group compression apparatus comprising compression section length determining means for determining the length of the compression section in the measurement direction according to the degree of change in the group.