JPH05344356A - Image data compression and extension method - Google Patents

Abstract

PURPOSE:To display large sized image at a high speed by dividing images into plural areas, compressing them for each area, and extending the only corresponding compression data while discriminating which area of the image is required. CONSTITUTION:For example, the large sized image is split into five areas in the vertical direction and split into ten areas in the horizontal direction, which are divided into areas 1 to 50 and are separately compressed. When the compression data are stored in a compression image file 201, an index section 203 is provided at the head part to store the compression data of the areas 1-50 in compression data 205-1 to 205-50. When the compressed large sized image is displayed, the index section 203 is read to find out the position range of the part to be displayed in the entire image. Then, the only corresponding data are read out from the compression image file 201 for extension and display with the use of the index data in the index section 203.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to image data compression, and more particularly to an image data compression / decompression method capable of displaying a large format image at high speed.

[0002]

2. Description of the Related Art In recent years, computer applications that use, store, and transmit not only character data but also image data in large quantities have become more and more important. Since such image data has an extremely large amount of data compared to character data, etc.,
When it is stored in a disk memory or the like or sent via a communication line, information compression is often performed to reduce the required storage capacity and communication cost. Such compressed image data is decompressed when it is actually used for display or the like. As such an image compression / decompression method, for example, the LZH coding method, the MR coding method, the MH coding method or the like is used.

The speed of such image compression, decompression, and display is increasing in proportion to the improvement of the CPU performance. However, with the sophistication of applications, the resolution and size of the image and the image required there are increased. The number of cells is rapidly increasing, and there is a strong demand for higher display speed. Dedicated hardware is often used for such compression / decompression, and particularly when displaying a compressed large format image, a large CPU processing capacity and high-speed dedicated hardware are required.

In the conventional method for displaying a compressed image, the entire compressed image is once decompressed, expanded in the memory and then displayed on the display. Therefore, a large amount of memory is required to accommodate all the decompressed images. For example, an image having a size of A1 and a size of 300 dpi in monochrome is uncompressed in a system with a small memory because the expanded image is close to 4 Mbytes. In order to prevent the expanded image data from occupying a large amount of memory all the time, the compressed data is usually kept in the memory and expanded every time the display is needed. There is a problem that the display speed becomes slow. Problems like this
It is particularly serious in applications such as CAD that handle large-format images.

Furthermore, when displaying a large format image,
It is often only part of what is actually displayed on the display. However, in the conventional decompression method, it is necessary to decompress the entire compressed image data in such a case due to the nature of the compressed data, and there is a problem that the memory and time required for the decompression increase.

In order to reduce such a problem, when it is necessary to display a part of an image, the compressed image data is expanded from the beginning, and all the parts necessary for display are expanded. It is also performed to detect the fact that the expansion processing is terminated. However, when such a method is used, high-speed display is performed when the part that needs to be displayed is the part that can be obtained in the initial stage of the decompression process, but on the contrary, it cannot be obtained until the end of the process. In the case of a non-existing portion, a display speed as slow as the method of first expanding the entire image can be obtained.

[0007]

[Objective] The present invention solves the above-mentioned problems of the prior art,
At the same time, it is an object of the present invention to provide an image data compression / decompression method capable of decompressing / displaying large format data compressed only in a part thereof at high speed.

[0008]

According to a preferred embodiment of the present invention, large-format image data is divided into a plurality of areas. The compression of the image data is performed not for the entire image data collectively but for each area and stored as compressed area data. When decompressing and displaying a part of the image data, the area actually required in the image data is determined, and the compressed area data corresponding to the area is decompressed and displayed.

Further, in this embodiment, the image data is
The compressed data that has been reduced at several reduction ratios is also stored together with the original size data. As a result, even when the image is viewed in a wider range than usual or in the entire image, the image display can be speeded up as compared with the case where only the original size data is stored.

[0010]

The present invention will be described in detail below with reference to examples. FIG. 1 shows an example in which the image data represented by a bit map is divided into a plurality of areas. In FIG. 1, a rectangular large image, for example, an A1 size image 101 is vertically divided into five,
It is divided into 10 in the horizontal direction and divided into 50 rectangular regions 1 to 50. Each of these 50 areas is compressed as one image data represented by a bit map and is compressed independently of other areas. The compression method used when compressing the individual regions can be the same as the conventional technique.

The compressed data obtained by compressing the areas 1 to 50 in this manner are collectively stored in one compressed image file 201 as shown in FIG. In FIG. 2, an index portion 203 is placed at the beginning of the compressed image file 201, followed by area 1 to area 1.
Compressed data 205-1 to 205 obtained by compressing each area of 50
-50 are placed in order.

The index unit 203 stores compressed data 205-
The position (for example, offset from the beginning of the file) of each of Nos. 1 to 205-50 and the size thereof (even if the size of the region before compression is the same, the image in each region after compression) Note that the size of compressed data usually changes according to the complexity of, etc.).

The process of decompressing and displaying the image data compressed in this way will be described below.

When an application needs to display a compressed large-sized image, the index section 203 in the compressed image file 201 in which the application is recorded is first read into the memory. When the range of the position of the portion to be actually displayed in this large format image within the entire image (such as the coordinates of the bitmap) is determined, the application determines the range to be displayed within regions 1 to 50. Find all areas that are partly or wholly. This process can be easily realized because it is known which range the regions 1 to 50 respectively occupy in the image. Only the compressed data (a part of 205-1 to 205-50) corresponding to the area found in this way is read from the compressed image file 201 using the index data in the index unit 203 and decompressed. To do.

For example, consider a case where the displayable size is only a vertical 2 × horizontal 2 area. Here, the division coordinates of the displayed portion (represented by numbers 1 to 10 and 1 to 5 respectively written on the upper and right sides of the image 101 in FIG. 1) are (2, 1), (3, 1), (2, 2), (3
In the case of 2), only the areas 2, 3, 12, and 13 are displayed, so the compressed data 205-2, 205-3, and 205 corresponding to these in the compressed image file 201 are displayed.
Only -12 and 205-13 are read and expanded.

As a result, the expansion process is completed in an extremely short time as compared with the conventional case, so that the display of a large format image is speeded up.

It is also possible to scroll a portion (display window) actually displayed on the display device in the large-sized image in an arbitrary direction. To do this, keep track of where the display window is currently in the large format image, and once it is out of the decompressed area that has been expanded in memory, and a portion of it will go to another area, Compressed data 205 corresponding to the other area
-1 to 205-50 are read from the compressed image file 201 and decompressed. Since the process itself for scrolling that should be performed after this expansion is a well-known matter, it will not be described here in particular.

When handling a large-sized image, in order to give an overview of a portion which is displayed at a full-size display at a time in a wider range including the portion or the entire image,
Thumbnails are often displayed. When only the compressed data of the full-size image is stored, it is necessary to temporarily expand the full-size area including the portion actually reduced and displayed in the image. Therefore, even if the expansion processing is performed only for the necessary areas as described above, it is necessary to expand the compressed area data corresponding to a large number of areas as the reduction rate increases. As a result, the amount of calculation for expanding the image increases, and the speed of the reduced display is considerably slower than that in the case of the original size. In order to avoid this problem, in the present embodiment, when the reduced display is performed, the reduction ratio is normally 1/2, 1/4,
Focusing on the fact that a power of 1 such as 1/8, 1/16, etc. is often used, the compressed image file 201 is provided with image data of several reduction ratios in advance. There is.

Returning to FIG. 2, in the compressed image file 201, the compressed data 205-50 of the area 50 is recorded after the position where the compressed data 205-50 is recorded.
Compressed data of 07 and 1/16 times images are recorded. Images with other reduction ratios should be calculated from data with lower reduction ratios. For example, reduction ratio 1
When it is requested to display an image at a reduction ratio of ½ or ⅛, compressed data 203-
Image data having a required reduction ratio is created by decompressing the necessary data of 1 to 203-50 or the compressed data 207 of the 1/4 times image and then reducing the data.
In this case, (1+
(1/4) x (1/4) + (1/16) x (1/1
6)) = 1.07 times the size is slightly increased, but the reduced image is displayed faster. Of course, when compressing these reduced images, instead of compressing the entire reduced image, it is possible to divide the image into a plurality of regions as in the full-scale image and compress each region.

Needless to say, the present invention is not limited to the embodiment described above.
For example, in the embodiment, the data obtained by compressing each area obtained by dividing one image is combined into one file, but the compressed data of each area may be stored in one file.

When the result of compressing the image may be immediately expanded and displayed, the image may be stored in the memory instead of being stored in the external storage device. If a higher speed display is required and there is enough memory, the entire compressed image file is loaded on the memory and the compressed data corresponding to the required area is taken out from the loaded file. You may do it.

[0022]

As described above in detail, according to the present invention,
High-speed display of compressed large-format image data is possible. Also, large format images that were previously impossible on systems with only a small amount of memory, such as A1
You will be able to refer to images of size 300 dpi. Further, the reduction display of large format data can be speeded up.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of division of image data into a plurality of areas.

FIG. 2 is a diagram showing an example of a structure of a compressed image file in which compressed data of each area is recorded.

[Explanation of symbols]

 1 to 50: area 101: image 201: compressed image file 203: index section 205-1 to 205-50: area compressed data 207: 1/4 times compressed image data 209: 1/16 times compressed image data

Claims (3)

[Claims] 1. A method for compressing image data, wherein one image data is divided into a plurality of areas and each of the plurality of areas is compressed. 2. A method for decompressing image data compressed by the image data compression method according to claim 1, wherein compressed data corresponding to a necessary area of the plurality of areas is selected and expanded. Image data decompression method. 3. An image data compression method for storing, in addition to compressed area data corresponding to each of a plurality of areas obtained by dividing image data, compressed image data obtained by compressing data obtained by reducing the image data.