JPS6261988B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image compression and decompression device that compresses gradation image data obtained by a computerized tomography device or the like.

This type of computerized tomography apparatus is a device that obtains image information about the cross section of the subject through image reconstruction processing based on projection data from multiple directions on the subject.
Tomography) device.

The reconstructed image data in the CT device is a numerical value of ±1000 defined as -1000 for air and +1000 for bone, or -500 for air and +500 for bone, depending on the radiation transmission absorption coefficient for each pixel. It is represented by gradation data called CT number, which consists of a numerical value of ±500.

Conventionally, when storing the CT number in an external storage device, etc., the CT number was stored as 2 bytes (16 bits) per pixel, so for example, the entire screen consisted of 320 x 320 pixels. When composed of matrix images, approximately 200K bytes of storage capacity is required to store the reconstructed image data of the entire screen (one image).
The storage efficiency of magnetic disks, magnetic tapes, and the like as external storage devices, that is, the utilization efficiency of storage media, has been poor.

The present invention was made based on the above circumstances, and an object of the present invention is to provide an image compression/decompression device that can efficiently compress or restore image data in order to improve the utilization efficiency of storage media. .

That is, the image compression and decompression device according to the present invention has the following features:
The difference data between adjacent gradation image data is expressed with a data length shorter than the data length of the current image data to be compressed, and the difference data is expressed as compressed data, and the maximum value that the difference data can be represented by the set difference data length. an image compression means for adding compression adjustment data to the compressed data to indicate that it has exceeded the limit to obtain compressed image data; and restoring the compressed data in the compressed image data to obtain restored data and adding the compression adjustment data and an image restoration means for adding corresponding restoration adjustment data to the restoration data to obtain restored image data, so that the image can be efficiently compressed and stored in a storage medium, and can also be read out from the storage medium and restored. This allows almost the same image data to be obtained.

When applying the method of taking the difference values between each data item, which is known as a means of compressing large amounts of data, to a CT device, we investigated the distribution of difference values in the reconstructed image data of the CT device and found the following. The following results were obtained.

That is, as shown in FIG. 1, the CT numbers of each picture element of the reconstructed image data are respectively a ₀ , a ₁ , a ₂ . . .
..., and the difference value of the CT number of each picture element (a ₁
−a ₀ ), (a ₂ −a ₁ ), (a ₃ −a ₂ )..., respectively, as b ₀ ,
Let b ₁ , b ₂ .... Such difference values b ₀ , b ₁ , b ₂
Regarding ..., the relationship between the difference value range and the ratio (%) of the number of difference value data included in it to the total number of data, for example, two types of concrete reconstructed images of the human abdomen (sample 1 and sample 2). The expression for this is shown in Figure 2. In this case, sample 1 and sample 2 are both data when the CT number is set to ±500. Here ±127 or −
Focusing on the difference value range from 127 to +127, it can be seen that approximately 92% of the data in sample 1 and approximately 96% of the data in sample 2 are included in this range. Also,
The difference value when the CT number is ±1000 is also ±
It can be easily inferred from FIG. 2 that most of the data will be contained within the 127 difference value range. In the above, we focused on the difference value range of ±127 because
Values in this range can be expressed as 8-bit data, and this is because a byte (8-bit) machine, that is, 8-bit parallel processing, is the most readily available and highly versatile processing device. That is, in a processing device for 8-bit parallel processing, processing such as loading, storing, and comparing data in units of 8 bits can be performed in one step, so the number of processing steps is correspondingly reduced, and processing time is also saved. This data processing in 8-bit units is employed in many current data processing devices, storage devices, and the like.

Therefore, in one embodiment of the present invention described below, data whose differential value can be expressed in 8 bits is expressed as a differential value, and data that cannot be expressed in 8 bits is compressed using 16-bit original data. It shall be.

An embodiment of the present invention will be described with reference to the drawings.

FIG. 3 shows the system configuration. In the figure, a reconstruction processing device 1 performs image reconstruction processing on a large number of projection data and outputs it as reconstructed image data DO ₁ , which in this case is 16-bit original data. The data compression device 2 compresses the image data DO ₁
is used as original data, and is output as compressed data DS by performing data compression processing as described below. The storage device 3 writes and reads the compressed data DS to and from storage media such as a magnetic tape 31 and a magnetic disk 32, for example. The data restoration device 4 performs data restoration processing as will be described later on the compressed data DS read out from the storage device 3 to restore the original data, that is, the original reconstructed image data.
Output as image data DO ₂ corresponding to DO ₁ .
The display device 5 displays a reconstructed image based on the image data _DO2 .

Data compression processing in the data compression device 2 is performed as follows.

As shown in Fig _. 4, among the 16-bit original data _{a 0 ,} a ₁ , a ₂ .
This is the first data of the DS. Next, the original data a ₁
Take the difference value (a ₁ − _{a 0} ) between and a ₀ , and this difference value is ±
If it is within the range of 127, the difference data _b1 consisting of the lower 8 bits of the binary data representing the difference value is set as the second data. In addition, if the difference value (a ₁ - _{a 0} ) is outside the range of ±127, the code indicating overflow is 10000000 (8 bits - originally -128
), and the 16-bit original data is added to this code.
Set a ₁ as the second data (total of 24 bits including code data). Next, the difference value (a ₂ −a ₁ ) between the original data a ₂ and a ₁ is taken, and the third data is obtained in the same manner as described above. Thereafter, the original image data DO ₁ is processed in the same manner as compressed data DS.

Further, the restoration of the compressed data DS in the data restoration device 4 is performed as follows.

First, the first 16 bits of the compressed data DS are used as the first data of the restored image data _DO2 . Next, it is determined whether the following 8 bits are the above-mentioned overflow code (10000000), and if they are not overflow codes, the 8 bits are differential data.
Since b is ₁ , it is added to the previous restored data, in this case the first data (lower 8 bits thereof), to form the 16-bit second data. Also,
If the 8 bits are overflow codes, the following 16 bits are original data, and are therefore used as the second data. Thereafter, the compressed data DS is processed in the same manner as restored image data _DO2 .

With such a configuration, the reconstruction processing device 1 can be used. The reconstructed image data DO ₁ is compressed by the data compression device 2 and stored in the storage device 3 as compressed data DS. In this case, according to the data compression process described above in the data compression device 2, for example, the data of sample 1 shown in FIG.
Extremely highly efficient data compression is performed, with the compressed data DS being about 5% of DO ₁ and about 54% of sample 2. Therefore, the utilization efficiency of storage media such as the magnetic tape 31 and the magnetic disk 32 in the storage device 3 is improved, and a large amount of image information can be stored with a small storage capacity. Furthermore, when the compressed data DS stored in the storage device 3 is read, the data restoration device 4 converts the difference data b1 into (lower 8 bits of) the first data, for example, if it is the second data. The image data can be restored by addition, and thus the restored data DO2 is restored to have the same content as the original image data DO1, and can be provided to the display device 5 or the like.

In this way, data is compressed and recorded by making the difference value between each picture element of the original image data into 8-bit data, and storing the data whose difference value does not fit within 8 bits as 16-bit data. Therefore, the method of compressing and storing reconstructed images of a CT device has high data compression efficiency and is easy to implement.

Therefore, by adopting the above configuration, the utilization efficiency of the storage medium in the CT apparatus is improved, and the number of images stored on magnetic tapes, magnetic disks, etc. is increased. It becomes possible to use a storage medium with a relatively small capacity. Moreover, this also makes it possible to reduce the cost per image of the required storage medium, and it also becomes possible to reduce the cost of the entire system.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with various modifications without changing the gist.

For example, in the above embodiment, the reconstruction processing device 1, the data compression device 2, and the data restoration device 4 have been described as independent hardware, but these image reconstruction processing means, data compression means, and data restoration means are implemented by a computer. It is also possible to use a processing device such as the above in common and realize each process by software.

In addition, when compressing data, a separate 1-bit table is created for each data (picture element) that makes up the original image data, and it is determined whether the difference value is stored as 8-bit data or 16-bit data. It is also possible to store the information and allocate 8 bits to difference values in the range of -128 to +127, and allocate 16 bits to those exceeding the range. In this case, when allocating 16 bits, the original data can be stored instead of the difference value.

Furthermore, not just a difference value but a difference value between difference values, that is, a second-order difference value or a higher-order difference value may be used as the difference data to achieve further data compression.

As described above, according to the present invention, image data can be efficiently compressed in order to improve the utilization efficiency of storage media, and moreover, image data can be restored to almost the original image data before compression. equipment can be provided.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining reconstructed image data, FIG. 2 is a diagram showing an example of the distribution of difference values in reconstructed image data, and FIG. 3 is a system block diagram showing the configuration of an embodiment of the present invention. 4 are diagrams for explaining the state of data compression in the same embodiment. 1... Reconfiguration processing device, 2... Data compression device, 3... Storage device, 4... Data restoration device, 5
... Display device, 31 ... Magnetic tape, 32 ... Magnetic disk.

Claims (1)

[Scope of Claims] 1. Difference data between adjacent gradation image data is expressed with a data length shorter than the data length of the current image data to be compressed, and the difference data is expressed as compressed data, and the difference data is the set difference data. an image compression means for adding compression adjustment data indicating that the maximum value that can be expressed in data length is exceeded to the compressed data as compressed image data; and restoring the compressed data in the compressed image data to generate restored data. 1. An image compression and decompression device comprising: image decompression means for obtaining decompression adjustment data and adding decompression adjustment data corresponding to the compression adjustment data to the decompression data to obtain decompressed image data. 2. The image compression and decompression apparatus according to claim 1, wherein the difference data is a multi-level difference value. 3. The image compression and decompression apparatus according to claim 1, wherein the data length of the compression adjustment data is set equal to the data length of the difference data. 4. The image compression and decompression apparatus according to claim 1, wherein the data length of the compression adjustment data is set to a data length of 1 bit. 5. The image compression and decompression apparatus according to claim 1, wherein the decompression adjustment data is the current image data to be compressed and is added immediately after the compression adjustment data. 6. The image compression and decompression apparatus according to claim 1, wherein the restoration adjustment data is set to be equal to the difference data and have a data length equal to the data length of the current image data to be compressed.