JP2620382B2 - Digital signal group compression method and apparatus - Google Patents

Description

The present invention relates to a digital signal for compressing an original digital signal group whose value changes in one measurement direction into a compressed digital signal group having a smaller number of signals. The present invention relates to a group compression method and apparatus.

[Conventional technology]

In general, to convert an arbitrary amount of change into an original digital signal group whose value changes in one measurement direction, and to improve the efficiency when this original digital signal group is further used,
The tendency of the value change corresponds to the original digital signal group, but the number of signals is compression-converted to a compressed digital signal group smaller than the number of original digital signal groups.

As an example of compressing such a digital signal group,
For example, as shown in FIG. 22, there is a case where an arbitrary image 1 is printed on a sheet 3 as a reproduced image 1a.

More specifically, FIG. 22 shows a case where the image 1 and the character 2 shown at the leftmost part are edited and printed on the paper 3 as the reproduced image 1a and the reproduced character 2a as shown at the rightmost part. I have. One character 2 is converted into a digital signal by a character data input device 4 such as a keyboard, and is input to the host computer 6 as character data. The other image 1
Is read as image data by an image data input device 5 such as an image scanner and input to the host computer 6. The image data read from this image 1 is
The density of the image 1 is defined as an original digital signal composed of a set of digital signals measured for each unit pixel along the scanning direction of the scanning line. If this original digital signal is used as it is for printing the image 1, the amount of information is too large, and a large load is imposed on a control device such as a CPU of the host computer 6 or the printer 7, and these are formed with higher performance than necessary. Have to be expensive.

Therefore, conventionally, a compressed digital signal having a small number of signals which changes while changing according to the change of the original digital signal is created, and the host computer 6 edits the image 1 and the character 2 using the compressed digital signal. It is supposed to do it. The print data created by the host computer 6 is sent to a printer 7, and the printer 7 prints the reproduced image 1a and the reproduced characters 2a on the paper 3 based on the received print data.

[Problems to be solved by the invention]

However, the conventional method of compressing the original digital signal group has the following problems.

That is, reading of the density of the image 1 by the image data input device 5 is performed by repeating the measurement in the y direction while scanning the image 1 shown in FIG. 22 in the x direction.

FIG. 23 shows image data comprising the density of the image 1 along one scanning line obtained by scanning the image 1 in the x direction by the image data input device 5.
This image data is obtained by displaying the tone values of the density measured for each pixel in the x direction of the image 1 as digital signal values and displaying these digital signal values as a line graph, and the values change in the x direction. It is a kind of original digital signal group. When compressing this image data, as shown in FIG. 23, the whole scanning direction range of the image 1 in the x direction is equally divided in the x direction by a plurality of compression sections having an equal width, and divided in each compression section. The original digital signal group is compressed so as to be one compressed digital signal.

However, like the image data shown in FIG. 23, the original digital signal group often includes a high-frequency component region whose value changes drastically and a low-frequency component region whose value changes gradually. In order to compress the high-frequency component so as to change with good response 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, more compressed digital signals are generated than necessary in the low-frequency component region, which results in poor data compression efficiency including excess data as a whole. In addition, a large load is imposed on various subsequent control processes in the printer 7. For this reason, in the above-mentioned conventional method, it was 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.
A digital signal group that can efficiently compress an original digital signal group whose value changes in two measurement directions into a compressed digital signal group that changes in response to the change in a small compression section It is an object to provide a compression method and apparatus.

[Means for Solving the Problems] To achieve the above object, a digital signal group compression method according to the present invention according to claim 1, wherein an original digital signal group whose value changes in one measurement direction, In the digital signal group compression method in which compression is performed using a plurality of compression sections divided in the measurement direction, when determining a start point and an end point of the compression section, values in the data of the original digital signal are determined. The pixel positions having a large change degree are section point candidates, the section point candidates are narrowed down to a predetermined number to form section points, a compressed digital signal group based on each of the section points is created, and the compressed digital signal for the original digital signal group is generated. Calculate the group approximation accuracy (S / N ratio) for each compression section,
An error variance of a compression section in which the approximation accuracy exceeds a first predetermined value is obtained, and when the error variance is equal to or more than a second predetermined value,
A section point is added to a position where the error is large, and if the error variance is less than the second predetermined value, a section point is added to the center point position of the compression section, and a compressed digital signal group is created again. A process for obtaining the approximation accuracy is repeated until the approximation accuracy becomes equal to or less than the first predetermined value.

The digital signal group compression device according to the present invention according to claim 2, wherein a change degree calculating means for calculating a change degree of the value in the measurement direction of the original digital signal group whose value changes in one measurement direction; Compression section length determining means for obtaining the length of the compression section in the measurement direction according to the degree of change of the original digital signal group obtained by the degree of change calculating means, which serves as a start point and an end point of the compression section When determining a section point, a pixel position having a sharp change in value in the data of the original digital signal is defined as a section point candidate, the section point candidates are narrowed down to a predetermined number, and the narrowed down section point candidates are defined as section points. Compression section length determining means for performing compression, a signal compression means for compressing an original digital signal group using the compression section determined by the change degree calculating means and the compression section length determining means, An approximation accuracy calculating means for obtaining an approximation accuracy (S / N ratio) of the compressed digital signal group obtained by the stage with respect to the original digital signal group for each compression section; If the error variance of the compression section is equal to or greater than a second predetermined value, a section point is added to a position having a large error until the compression interval exceeds a predetermined value. If the error variance is less than the second predetermined value, a signal is issued by adding a section point to the center point of the compression section to cause the signal compression means to add a compression section and recompress the signal. Compression section addition instruction means.

(Operation)

According to the present invention, by operating the device of the present invention in accordance with the method of the present invention, a compressed digital signal group obtained by efficiently compressing the original digital signal group can be obtained.

That is, the compression unit generates a compressed digital signal by performing compression based on a plurality of compression sections whose lengths in the measurement direction are unequal according to, for example, the degree of change in the value of the original digital signal group in the measurement direction. Thereafter, the approximation accuracy calculating means obtains the approximation accuracy of the obtained compressed digital signal group with respect to the original digital signal group. If the approximation accuracy is not a predetermined value, the compression section addition instructing means makes the approximation accuracy a predetermined value. Until then, a new compression section is added to the compression section with low approximation accuracy for the compression means, and recompression is performed. As a result, a group of compressed digital signals with high compression efficiency that responds to changes in the values of the original digital signal group with good responsiveness can be obtained.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 21.

In this embodiment, as shown in FIG. 1 and FIG. 2, as the original digital signal group, image data composed of the shading degree of the image 1 is used as in the related art.

FIG. 1 schematically shows a digital signal group compression device 11 according to the present invention.

The digital signal group compressor 11 of the present embodiment compresses an original digital signal group whose value changes in one measurement direction using a plurality of compression sections whose lengths in the measurement direction are unequal. A compression unit 12, an approximation accuracy calculation unit 13 for obtaining an approximation accuracy of the compressed digital signal group obtained by the compression unit 12 with respect to the original digital signal group, and an approximation accuracy obtained by the approximation accuracy calculation unit is a predetermined value. A compression section addition instructing means for issuing a command to add a new compression section to the compression section having a low approximation accuracy and to recompress the compression section with a low approximation. The compression means 12 is 1
Change degree calculating means for calculating the degree of change in the measurement direction of the original digital signal group whose value changes in two measurement directions, that is, the degree of change in the x direction of the image data consisting of the gradation values of the density of the image 1 15, a compression section length determining means 16 for determining the length of the compression section in the measurement direction, that is, the length in the x direction, according to the degree of change of the image data obtained by the change degree calculating means 15; The signal compression means 17 which converts the original digital signal into one compressed digital signal in accordance with a predetermined method using the compression section determined by the determination means 16
have. In addition, the operation of each of these means is related.
A CPU 18 is provided.

 Next, the operation of the present embodiment will be described.

In this embodiment, as shown in FIG. 3, the entire scanning direction range of the image data is divided into unequal compression sections having different section lengths, that is, different lengths in the x direction, and the original digital The signal group is converted into one compressed digital signal.

To explain this operation outline flowchart of FIG. 4, when the compression operation is started, first, as shown in step ST _11, the detection scanning in the x direction of a certain concentration of the image 1 is performed by the image data input unit 5 Then, the image data is read, that is, the original digital signal group is read. Next, as shown in step S _12, the compression section is set by the degree of change calculation unit 15 and the compression section length determining unit 16. That is, the change degree calculating means 15 calculates the change degree of the value of the original digital signal group, and the compression section length determining means 16 determines the length of the compression section according to the change degree. Next, in step ST _13, in accordance with a predetermined method using the compression section by the signal compression unit 17,
Create a compressed digital signal group. Next, step ST ₁₄
In, the approximation accuracy calculating means 13 obtains the approximation accuracy of the compressed digital signal obtained by the compression means 12 with respect to the original digital signal, and compares this approximation accuracy with a predetermined value set in advance for each compression section. This approximation accuracy is compressed when placed in a predetermined value is ended, if not enter the predetermined value, it proceeds to step ST _15. In this step ST ₁₅ is the compression section add instruction means 14, adds a new compression section to lower approximation accuracy compression within an interval, signal compression processing is performed back to the step ST ₁₃ again, in the subsequent step ST ₁₄ The approximation accuracy is determined.

The processing in step ST ₁₅ → ST ₁₃ → ST _14, the approximation accuracy of the compressed digital signal is performed repeatedly until it enters the predetermined value.

Wherein at the setting of the compression section in the step ST ₁₂ include various methods, such as the image data shown in FIG. 3, for the original digital signal group including a high frequency component region, severe degree of change of the value By shortening the length of the compression section of the part and increasing the length of the compression section of the part with a gradual change in the value, the compressed digital signal group that responds well to the change in the value of the original digital signal group Obtainable.

Further, in order to perform the setting of the compression section in the step ST ₁₂ specifically performs smoothly and properly by determining the interval point as a start point and an end point of each compression section indicated with black circles on the x-axis in FIG. 3 be able to.

The selection of the section point may be performed by the change degree calculating means 15 and the compression section length determining means 16 according to, for example, the flowchart shown in FIG.

That is, a plurality selects the x coordinate of the pixel positions or pixels of intense part of the degree of change than the image data of FIG. 3 as a section point candidates in step ST _21. Next, in step ST _22, a plurality of sections points candidate set was elected as the, narrowed down to a predetermined number of sections point candidates. Next, in step ST _23, a manner narrowed section point candidates as said is narrowed down to those that are separated by a predetermined minimum pixel or number. Next, in step ST _24, to replenish the new segment point candidate number corresponding to the number that is reduced by narrowing the step ST _23, obtains the section point candidate of the predetermined number.

An example in which the flowchart of FIG. 5 is further embodied is the flowchart of FIG.

With further description of this FIG. 6, to select a plurality of sections point candidates in step ST _31. This selection is to select a place where the degree of change of the image data is sharp,
As a selection method, for example, a pixel satisfying the following conditions (1) and (2) may be selected.

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 the i position in the x direction be g _(i) .
When D _(i) = g _{(i + 1)} −g _(i) , (1) D _(i-1) · D _(i) <0 (2) max (| D _(i-1) | , | D _(i) |)> C where C is a location that satisfies both conditions consisting of a constant (default).

The conditions (1) and (2) are such that the digital signal of the pixel portion whose x coordinate is (i) changes positively and negatively between the digital signal of each pixel portion before and after the unit pixel by the unit pixel. In addition, the condition is that the product of the absolute values of the respective amounts of change exceeds the degree of the intensity of the amount of change that is equal to or more than the predetermined number C.

Next, in step ST _32, for each section point candidates selected in the step ST _31, the following equation max order from the larger of the calculated value _{(| D (i-1)} |, | | D (i)) Is given. in this case,
If there are a plurality of section point candidates having the same calculated value and it is necessary to select them, for example, the x-coordinate values of the pixels are selected in ascending order.

Next, in step ST _33, from the section point candidate set, a predetermined number (e.g., 30) selects the section point of the upper.

Next, in step ST _34, the section point candidate 30 that is elected, whether the neighborhood condition mutual spacing is within a predetermined minimum pixel count determination is made. If the interval point candidate is located in the vicinity is determined that YES proceeds to step ST _35, the section point selection operation is determined to NO if not in the vicinity of ends.

Next, in step ST _35, to remove the one from the two sections point candidates and neighboring points to each other, leaving the other as a section point candidate. In this case, assuming that the interval point candidates of the points having the x-coordinates i and j are close to each other, | D _(i-1) · D _(i) | and | D _(j-1) · D _(j) Compare with | and keep the larger value and delete the other.

Next, in step ST _36, it is determined whether the total number of sections point candidates have been elected to date is a predetermined number which defines the step ST ₃₃ (30 in this embodiment), in the case of YES in section When the point selection operation is completed, if NO, step ST
Proceed to ₃₇ .

Above In this step ST _37, those not in the predetermined number (30) missing minute already near relationship and the section point candidates have been elected a new segment point candidate number to, as in step ST ₃₂ in addition, it elected to order from, and returns to step ST _36.

The operation in steps ST ₃₆ and ST ₃₇ are repeating example until the determination in step ST ₃₆ is YES, and the interval point selection operation ends.

By determining the section points in this way, as shown in FIG. 3, a compression section formed between the section points is determined. The compression section is set such that the section length becomes shorter in the high frequency component region and becomes longer in the low frequency component region.

Thereafter, in step ST ₁₃ shown in FIG. 4, the compressed digital signal with each compression interval is determined, the compressed digital signal group of one scanning direction as a whole is determined.

Figure 7 shows a step ST ₁₃ after the operation of the Figure 4. That is, performs reading of the original digital signal group in step ST _41, after setting the initial compression section in step ST _42, the compressed digital signal is obtained as shown in step ST ₄₃ after. Step ST ₄₃
In, an equation for determining an approximate function for obtaining a compressed digital signal for each of the plurality of compression sections obtained as described above is created. Next, in step ST _44, seeking the solution of the equation for each of the compression section, to create a compressed digital signal group. Next, in step ST _45, obtains approximation accuracy of the original digital signal group of the compressed digital signal group was determined (S / N ratio) by computing for each compression period. Thereafter, in step ST _46, the calculated approximation accuracy is determined whether or not within the predetermined value, proceeds to step ST ₄₈ in the case of NO, i.e., if YES is step S
It proceeds to T _47.

In this step ST _47, by performing addition of a new segment point lower approximation accuracy compression section, perform additional compression section. Thereafter, the process returns to step ST ₄₃ and step ST _44, again it obtains the compressed digital signal group including the added compression section, determined followed by approximation accuracy for compressed digital signal group which is updated in step ST _45, step In ST ₄₆ , it is determined whether or not the approximation accuracy falls within a predetermined value.

The operations of these steps ST ₄₇ , ST ₄₃ , ST ₄₅ , ST ₄₆ are repeated until the determination in step ST ₄₆ is good.

Next, in step ST _48, the data of the approximate function is calculated as the compressed digital signal group, is the memory in the appropriate memory, and ends as may be subjected to a subsequent use.

The setting of the additional compression section in the step ST ₄₇ of FIG. 7 there are a variety of ways, in this embodiment, adding a compression section by setting the additional segment point as shown in FIG. 8 Like that.

Referring to FIG. 8, it performs a ranking of candidate compression section for selecting the additional section points at step ST _51.

 This sequence will be described with reference to FIG.

FIG. 9 shows the already determined section points ξ ₁ , ξ ₂ , ξ ₃ , ξ ₄ , ξ
₅ shows the original digital signal group and the compressed digital signal group in the range of _{5. In} this embodiment, the approximation accuracy of the compressed digital signal group to the original digital signal group in each compression section between the section points is low. We rank in order from thing. The approximation accuracy in this compression section is obtained by the following equation.

Here, _ｉi is the x coordinate of the section point _ｉi , and L (t) and l (t) are the gradation values of the original digital signal group and the compressed digital signal group at the x coordinate (t). From this equation, that the approximation accuracy of the compression section is low means that the value of the equation is large.

Next, in step ST _52, a single compression zone one number from ranking candidate compression section selects a compression section for selecting the additional section candidate.

Next, in step ST _53, to determine how to add the section point, the error variance of the compression section selected in step ST ₅₂ it is determined whether or not 4 or more, in the case of YES in step ST proceeds to _54, in the case of NO proceeds to step ST _61. This error variance is obtained by the following equation.

Where dy (t) = L (t) -l (t) And

When the error variance is 4 or more, as shown in FIGS. 10 and 11, the degree of change in the difference between the original digital signal group and the compressed digital signal group is large in the measurement direction. In addition, when the error variance is less than 4, FIG. 12 and FIG.
As shown in FIG. 13, a state in which the degree of change in the difference between the original digital signal group and the compressed digital signal group is small in the measurement direction. If in the present embodiment, when the error variance is as large as 4 or more, so as to add a section point a large part of the errors in step ST ₆₀ from step ST _54, small and error variance is less than 4, step the center of the compression section in ST ₆₁ or later so as to add a section point.

In one step ST _54, the points in the candidate compression section performs ranking additional segment point candidates.

In this case, in this embodiment, FIGS. 14 (a) and 14 (b)
As shown in the figure, the difference between each value L (i) and l (i) of the original digital signal group and the compressed digital signal group at the x coordinate (i) other than the already determined section points at both ends of the candidate compression section. The absolute value | L (i) -l (i) | is obtained, and additional section point candidates are set in descending order.

Next, in step ST _55, as an additional segment point candidates, and one selects a number 1 of the candidate determined as described above.

Next, proceeds in step ST _56, the added section point candidate, whether section points already determined in the vicinity of only the unit pixel neighboring Ri is present is determined, in step ST ₅₇ in the case of NO and, in the case of YES proceeds to step ST _56.

In one step ST _57, the first 15 as shown in Figure (a), spaced from the additional segment point candidates of segment points already determined in the two neighboring xi] _{i + 1} and ξ _{i + 2 2} pixels or more Therefore, as shown in FIG. 7B, the additional section point candidate is set as an additional section point ξ _{i + 2,} and the order of the already determined section points having the larger x-coordinate is sequentially forwarded.

In the other step ST _58, the section points that have already been determined in the vicinity of the additional section point candidate is determined whether a single point, if YES, proceeds to step ST _59, the NO It proceeds to step ST ₆₀ in the case.

In one step ST _59, the Add section point a single point next to the additional segment point candidate as multiple point double. In this case, when a single point exists on both sides of the additional section point candidate, the single point having the smaller x-coordinate value is set as an additional section point as a double multiplex point. Fig. 16 (a)
In, since the interval points xi] _{i + 1} which has already been determined to be a single point only next left additional segment point candidate exists, the interval points xi] _{i + 1} as shown in FIG. (B) 2 An additional section point ξ _{i + 2} is added as a multiple point.
In the figure, the multiple points are indicated by white circles. In addition, in FIG. 17 (a), since there are already determined section points ξ _{i + 2} and ξ _{i + 3} which are single points on both sides of the additional section point candidate, FIG. 17 (b) As shown in the figure, an interval point having a small x coordinate value ξ _{i + 2} is set as a double multiplex point, and an additional interval point ξ _{i + 3}
Is to be added.

In the other step ST _60, as shown in FIG. 18 (a), previously determined interval point interval points xi] _{i + 1} of the multiple next additional segment point candidates, because it is xi] _{i + 2} , FIG.
The additional section point candidates are canceled as shown in FIG. Then, in order to set the following additional section point candidates, additional sections point candidates revoked segment point candidate, it is determined whether the last one of those in which the ranking in step ST _54, the YES returning to step ST _52, if, in the case of NO returns to step ST _55, for additional segment point candidates next rank, the setting processing of the additional segment point similar to the above.

Determination in step ST ₅₃ is advanced to step ST _61, if NO, the as shown in FIG. 19, the additional segment point candidate midpoint of candidate compression section.

Next, in step ST _62, similarly to step ST _56, performs a determination of whether existing segment points in the vicinity of the additional section point candidate is present. If NO, proceeds to step ST _63, If YES, it proceeds to step ST _64.

In one step ST ₆₃ is an additional interval point additional segment point candidates.

In the other step ST _64, similarly to step ST _58, whether a single a section point that has already been determined in the vicinity of the additional section point candidate is determined, in the case of NO in step ST Returning to step ₅₂ , the next candidate compression section is selected,
If YES, it proceeds to step ST _65.

In this step ST ₆₅ as in step ST _59, the additional section point a single point next to the additional segment point candidate as multiple point double. In this case, when a single point exists on both sides of the additional section point candidate, the single point having the smaller x-coordinate value is set as a double multiplex point to be an additional section point.

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

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

The quality of the printed reproduced image 1a is almost equal to the quality of the original image 1. This is created by the signal compression means 17 based on the compression section in which the section length determined by the change degree calculation means 15 and the compression section length determination means 16 in the compression means 12 of the digital signal group compression apparatus 11 is uneven. The compressed digital signal group thus obtained is connected so as to smoothly change in the x direction to produce a reproduced compressed digital signal, which is further converted by the approximation accuracy calculating means 13 and the compression section addition instructing means 14 into the original of the compressed digital signal group. This is because the reproduced compressed digital signal is created such that the approximation accuracy for the digital signal group is set to a predetermined value. That is, this reproduced and compressed digital signal changes substantially in the same manner as the original digital signal group composed of image data. Further, the compressed digital signal group is compressed and greatly reduced in information amount, that is, the data amount, as compared with the original digital signal group, so that the burden on the host computer 6 and the printer 7 is reduced. High-speed data processing can be enabled.

Next, each compressed digital signal group and each compressed digital signal obtained by performing a compression process on the same original digital signal group by the method of the present embodiment and the conventional method so as to smoothly change in the x direction. The connected reproduced and compressed digital signal groups are compared with each other with reference to FIGS. 20 and 21. No.
FIG. 20 shows the result by the method of the present embodiment, and FIG. 21 shows the result by the conventional method. In both figures, the image data to be compressed indicated by the solid line is composed of 256 pixels (there are two pixels on one scale), and the gray scale of the density of the image 1 is represented by a digital signal value for each pixel in the entire scanning direction range. is there.

In the method of the present embodiment, as shown in FIG. 20, a total of 49 compression sections (section points on the x-axis) where the entire scanning direction range is within a predetermined length range and the section lengths are different. (Indicated by black circles or white circles), and a compressed digital signal is created using the compression section. The length of the compression section needs to be short in the high-frequency component region, and when the fluctuation of the gradation value is extremely large, the section length may be “0”. (When the section length becomes "0", it is considered that the section points are duplicated on the same x coordinate (measurement direction).) In this embodiment, as shown in FIG. Are present in an overlapping state (points indicated by white circles), and are therefore divided into 49 compressed sections in total. The broken line in FIG. 20 indicates a reproduced compressed digital signal group obtained by connecting the reproduced compressed digital signals in a state where these compressed digital signals are reproduced. In FIG. 20, when the image data (solid line) and the reproduced compressed digital signal (dashed line) overlap, the image data which is the original digital signal group is shown with priority.

In addition, in the conventional method, as shown in FIG. 21, the entire scanning direction range is equally divided into a total of 81 compression sections (section points are indicated by black circles on the x-axis) having a uniform section length, and the compression digital Creating a signal group. The broken line in FIG. 21 indicates a reproduced compressed digital signal group obtained by connecting reproduced compressed digital signals in a state where these compressed digital signal groups are reproduced.

As can be seen by comparing FIGS. 20 and 21,
According to the method of the present embodiment, about 1/2 of the number of compression sections of the conventional method is used.
While the original digital signal is compressed with the number of compression sections, the obtained reconstructed compressed digital signal group is not inferior to that of the conventional example having a large number of compression sections,
It responds to the change in the value of the original digital signal group with good responsiveness. Therefore, according to the present embodiment, the original digital signal group can be compressed very efficiently.

In the above-described embodiment, the compression target is the original digital signal group including the shading degree of each pixel of the image 1.
Any digital signal group whose value changes in one measurement direction can be compressed.

As a method of determining the length of the compression section in the measurement direction, a method other than the above-described embodiments may be adopted.

For example, in the case where the each interval of 6 Figure predetermined number of sections point candidates determined in up to step ST ₂₄ of spaced apart predetermined maximum pixel over number of equally dividing the interval within the maximum number of pixels May be added, and the compression section may be determined using all of these section point candidates as section points.

Further, it is possible to add a section point with monotonicity exceeding a predetermined value. That is, in a monotonous section in which the tone value simply increases or decreases with an increase in the x-coordinate, the absolute value of the difference in the tone value between the start point and the end point of the section is equal to or greater than a predetermined value. The end point may be added as a section point candidate, and a compression section may be determined using all of these section point candidates as section points.

Furthermore, the method and apparatus of the present invention are not limited to the above embodiments, but can be variously modified as needed.

〔The invention's effect〕

As described above, the digital signal group compression method and apparatus according to the present invention are constructed and operated. Therefore, the original digital signal group whose value changes in one measurement direction can be changed in response to the change with good response. The digital signal can be compressed into a group, the compression can be efficiently performed with a small number of compression sections, and the subsequent signal processing can be performed easily and at high speed.

[Brief description of the drawings]

1 to 20 show an embodiment of a method and apparatus for compressing a digital signal group according to the present invention, FIG. 1 is a block diagram schematically showing the apparatus of the present invention, and FIG. FIG. 3 is a block diagram showing a case in which the present invention is applied to a printer which performs image reproduction. FIG. FIGS. 4 to 8 are flowcharts showing states of compression processing according to the method of the present invention. FIG. 9 is a view similar to FIG. 3 when selecting a candidate compression section to add a section point. FIG. 10 and FIG. 11 are similar to FIG.
FIGS. 12 and 13 are diagrams similar to FIG. 3 showing a case where the error variance is small, and FIGS. 14 (a) and (b) are explanatory diagrams for obtaining additional section point candidates at arbitrary positions, respectively. No.
15 (a) (b), 16 (a) (b), 17 (a)
(B) and FIGS. 18 (a) and (b) are schematic diagrams for explaining a method of setting an additional section point, respectively, and FIG. 19 is an explanatory diagram for obtaining an additional section point candidate at the middle point of a candidate compression section. , 20th
FIG. 21 is a diagram similar to FIG. 3 showing a specific example of application of the method of the present invention, and FIG. 21 is a diagram showing a conventional example for comparison with the present invention.
FIGS. 22 and 23 are the same as FIGS. 2 and 3, respectively, showing a conventional example. 11: Digital signal group compression device, 12: Compression means, 13
... Approximation accuracy calculation means, 14 compression section addition instruction means,
15 ... change degree calculating means, 16 ... compression section length determining means, 17 ... signal compression means, 18 ... CPU.

Claims (2)

(57) [Claims] 1. A digital signal group compression method for compressing an original digital signal group whose value changes in one measurement direction by using a plurality of compression sections divided in the measurement direction. When determining the start point and the end point of the section, a pixel position where the degree of change in the value in the data of the original digital signal is intense is set as the section point candidate, and the section point candidates are narrowed down to a predetermined number as the section point, A compressed digital signal group based on each of the section points is created, and an approximation accuracy (S / N ratio) of the compressed digital signal group with respect to the original digital signal group is obtained for each compression section, and the approximation accuracy is a first predetermined value. Calculate the error variance of the compression section that exceeds, if the error variance is greater than or equal to a second predetermined value, add a section point at a position where the error is large, and if the error variance is less than the second predetermined value, , Adding a section point to the center point position of the compression section, generating a group of compressed digital signals again, and calculating the approximation accuracy until the approximation accuracy becomes equal to or less than the first predetermined value. Signal group compression method. 2. A degree-of-change calculating means for obtaining a degree of change in a value in the measurement direction of a group of original digital signals whose value changes in one measurement direction, and an original digital signal obtained by the degree-of-change calculation means. A compression section length determining means for determining a length of the compression section in the measurement direction in accordance with a degree of change of the signal group, wherein when determining a section point to be a start point and an end point of the compression section, A compression section length determining unit that sets a pixel position having a sharp change in value in the signal data as a section point candidate, narrows down the section point candidates to a predetermined number, and sets the narrowed section point candidates as section points; Signal compression means for compressing the original digital signal group using the compression section determined by the degree calculation means and the compression section length determination means; and a compressed digital signal group obtained by the signal compression means Approximation accuracy of the original digital signal group (S / N
Ratio) for each compression section, and approximation accuracy obtained by the approximation accuracy calculation means
If the error variance of the compression section is equal to or greater than a second predetermined value, a section point is added to a position where the error is large, until the compression interval exceeds a predetermined value. If the error variance is less than the second predetermined value, by adding a section point at the center point position of the compression section,
Compression section addition instructing means for issuing a command to add a compression section to the signal compression means and perform recompression.