JPH04273788A - Recording media and image data compressing - Google Patents

Abstract

PURPOSE:To offer an image data compressing method with a small quantizing error while the image data can be compressed with high efficiency. CONSTITUTION:The image is area-divided so as to collect an approximate color portion. The vector quantization is performed for respective divided small areas, and the data of the approximate color are displayed by the representative color of one color and data are rounded. For respective areas, the table information of the representative color of the rounded result and label image data constituted of a color number on this table are prepared. The label image data being the image data in the bit compressed condition and the table information of the representative color are recorded to a recording medium.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image data compression method for bit-compressing image data, and a recording medium for image data compressed by this method.

0002

[Prior Art] When recording digital image data, such as a moving image or a still image, on a recording medium such as an optical disk,
It is desirable to be able to record as much data as possible by making the most of the limited recording capacity. For this purpose, the image data is compressed and recorded on a recording medium.

[0003] Conventionally, in order to compress this image data, D
VI (Digital Video Interacti)
ve) and DCT (Discrete Cosine T
Compression encoding methods such as (transform) have been proposed.

0004

[Problems to be Solved by the Invention] However, the conventional compression encoding methods described above have complicated encoding algorithms. For example, DCT requires a product-sum operation (floating-point multiplication), which results in a large-scale hardware configuration. In addition, a large capacity memory is required for decoding, a dedicated special chip is required, and a general-purpose DSP (Digital Signal Programmer) is required.
A decoder (digital signal processing processor) cannot be used, and the decoder becomes expensive.

Furthermore, since data is compressed using frame correlation of image signals, there is a drawback that if an error occurs during decoding, the influence of the error will propagate to other frames.

[0006] Therefore, the applicant of the present invention has devised a new image data compression method as described below.

FIGS. 12 and 13 are block diagrams of an example of encoding processing that implements this new image data compression method. Note that this figure is a conceptual configuration diagram of encoding processing.

In this example, one frame (one screen) of the original image data is composed of 256 pixels in the horizontal direction and 192 pixels in the vertical direction, as shown in FIG. 14A. One pixel is 15-bit digital data in which each of the three primary colors is represented by 5 bits. In this example, the original image data is compressed frame by frame as follows.

That is, one frame of data of the original image is supplied to the first area dividing unit 2 through the input end 1, and as shown in FIG. 14B, one frame of the image is divided into horizontal
The image data is divided into 48 first block area image data G1(0) to G1(47) consisting of 64 pixels×16 pixels vertically, and stored in each recording area of the register 3.

The image data G1(i) (i=0 to 47, the same applies hereinafter) of each first block area is then supplied to the first vector quantization means 4. In the example of FIG. 12, the image data G1(i) of each first block area is respectively provided with a first vector quantization means 4 and processed in parallel. However, without performing parallel processing in this way, image data G1
Of course, vector quantization processing may be performed sequentially from (0) to G1 (47). The same applies to each process described later.

[0011] In each vector quantization means 4, vector quantization is performed for each image data G1(i) of each first block area so that the colors appearing as pixels are within 16 colors. That is, if the total of the colors of pixels appearing in each first block area is within 16 colors, all the colors are taken as representative colors and each pixel data is left as is. In addition, if the total of the colors of pixels appearing in the image data G1(i) of each first block area is 16 or more, the quantization error is minimized. Pixel data is rounded so that the number of pixel colors is 16 or less. At that time, the selected 16 colors are set as representative colors.

This vector quantization method involves, for example, considering a three-dimensional color space in which the color components of the three primary colors red, blue, and green are orthogonal to each other, and determining the distance between each pixel in the color space. A method is adopted in which pixel data is rounded so that the colors of pixels in the first block area fall within the 16 representative colors by grouping pixels that are close to each other. Note that it is of course possible to use various vector quantization techniques that have been proposed in the past.

In this way, the image data G1(i) of each first block area rounded into 16 colors is supplied to the labeling means 5, and the following labeling process is performed on the image data G1(0) to G1(0) of each first block. G1 (47) is processed in parallel. In each labeling means 5, a table LUT1 (
i) is created (see FIG. 15A). Hereinafter, this table of color data will be referred to as a color conversion table.

Further, each labeling means 5 refers to the color conversion table LUT1(i), and converts the pixel data rounded into 16 colors of each first block area into the color conversion table LUT1 to which the color of the pixel corresponds. (i) Upper color number (0
~15) The first label image data Lab1 (
i) (see FIG. 15B). In this case, the color numbers on the color conversion table LUT1(i) are from 0 to 15, as is clear from FIG. 15, so they can be expressed using 4 bits. Therefore, through the vector quantization process described above, the data of 15 bits per pixel of the original image is bit-compressed into first label image data of 4 bits per pixel.

In this way, each labeling means 5 outputs image data G1(0) to G of each first block area.
1(47), color conversion table LUT1(0)~
A color conversion table LUT1 (47) and first label image data Lab1 (0) to Lab1 (47), each of which is image data representing a 4-bit color number, are obtained and temporarily stored in registers 6 and 7, respectively.

Color conversion table LUT1(0) to LUT1
(47) is recorded on a recording medium such as a CD-ROM in association with the image data of the frame.

In addition, each first label image data Lab1 (
0) to Lab1 (47) are respectively supplied to the second stage compression processing means 8.

FIG. 13 shows one first block area G1 (
This is an example block of the second stage compression processing means 8 for the label image data Lab1(i) in i).

That is, the first label image data of the first block area G1(i) from the register 6 is supplied to the second area dividing means 11. In this second area dividing means 11, as shown in FIG. 14C, each of the first block areas consisting of 64 pixels x 16 pixels (horizontal x vertical) is divided into 16 blocks each consisting of 8 pixels x 8 pixels (horizontal x vertical). It is divided into second block areas, and the first label image data G2(0) to G2(15) of each second block area is stored in each recording area of the register 12.

[0020]The first label image data G2(j) (j=0 to 15, the same applies hereinafter) of each second block area is as follows:
It is supplied to second vector quantization means 13. In the example of FIG. 13 as well, the second vector quantization means 13 is provided for each second block area, and parallel processing is performed.

Each vector quantization means 13 performs vector quantization on each label image data G2(j) of each second block area so that the number of colors appearing as pixels is four or less. In other words, if the total color of pixels represented by color numbers in each second block area is within four colors, all the color numbers are taken as representative color numbers, and each label pixel data is left as is. . In addition, if the total of the colors of pixels appearing in each second block area is four or more colors, the color number in that second block area indicates four colors or less so that the error is minimized. The pixel data is rounded so that At that time, the four selected color numbers are taken as representative color numbers.

In this way, the label image data G2(j) of each second block area rounded to a color number of 4 or less is supplied to the labeling means 14, and the following labeling process is performed in parallel.

That is, each labeling means 14 creates a table (hereinafter referred to as a color number conversion table) of color number data of 4 or less (each color number data is 4 bits) selected as a representative color number for each of the second block areas. L.U.
T2(j) is created (see FIG. 16A).

Furthermore, each labeling means 14 refers to the color number conversion table LUT2(j), and converts the first label image data rounded into four color numbers of each second block area into the color number of that pixel. The index number (0 to 0) of the color number on the color number conversion table LUT2(j) to which
3) Second label image data Lab2(j) expressed by
(see FIG. 16B). In this case, the index numbers of the color numbers on the color number conversion table LUT2(j) are numbers 0 to 3, as is clear from FIG. 16, so they can be expressed with 2 bits. Therefore, through the vector quantization process described above, the data of 15 bits per pixel of the original image is bit-compressed into second label image data of 2 bits per pixel.

[0025] Thus, from each labeling means 14,
Image data G2(0)~ of each second block area
Color number conversion table LUT2 (
0) to LUT2(15) and second label image data Lab2(0) to Lab2(15), which are image data consisting of the index number display of the color number conversion table, are obtained and temporarily stored in registers 15 and 16, respectively. Ru.

[0026] These color number conversion tables LUT
2(0) to LUT2(15) and second label image data Lab2(0) to Lab2(15) are recorded on a recording medium such as a CD-ROM in association with the frame. Therefore, the recording medium contains, for each frame, the color conversion table LUT1(i), the color number conversion table LUT2(j), and the second label image data Lab2(j) (i=0 to 47, j= 0 to 15) are recorded.

Decoder processing of the image data bit-compressed in this manner is performed as follows.

That is, first, for the image data of each second block area, color number conversion table LUT2(j)
With reference to , the second label image data Lab2(j) in which each pixel is 2 bits is decoded into the first label image data in which each pixel is 4 bits. Then, first label image data Lab1(i) in units of first block areas is decoded from the first label image data in units of second block areas. Next, referring to the color conversion table LUT1(i), the first label image data Lab for each first block area is
1(i), color data of 15 bits per pixel is restored.

That is, decoding processing can be easily performed using a conversion table. Therefore, DCT
Since this method does not require a large capacity memory such as the one shown in FIG.

[0030] In the above example, the first block area and the second block area are static (fixed) assuming that one screen is evenly divided and each consists of a predetermined plurality of pixels in length and width.
The area is divided into

However, when region segmentation is performed statically in this manner, the dynamic range of image data within each palette is large, resulting in large quantization errors. Therefore, depending on the content of the image, the boundaries of the regions may appear on the screen, or the quantization error may become larger than the limit. Therefore, it is difficult to increase compression efficiency.

In view of the above points, the present invention provides an image data compression method capable of reducing quantization errors and increasing compression efficiency by dynamically dividing regions, and a method for recording compressed image data. The purpose is to provide a recording medium that is

[0033]

[Means for Solving the Problems] In the image data compression method according to the present invention, a color portion that approximates an image consisting of a plurality of pixels is divided into a plurality of regions, and the image data of each divided region is Then, vector quantization processing is performed to compress data, and the number of bits per pixel is compressed.

[0034]

[Operation] Image parts having similar colors are grouped together to form one area, and a plurality of areas are formed for one screen to divide the image data into areas. At this time, image parts having similar colors do not need to be continuous, and may be discontinuous.

Vector quantization processing is then performed within this region consisting of image parts of similar colors. Therefore, quantization errors are reduced.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 are block diagrams of an example of an encoding device that executes an image data compression method according to the present invention. In this example, the compressed image data is
- Record in ROM. This CD-ROM is used as software for game machines, and the image data is highly efficiently compressed so that moving images can be played back.

In this example, as in the previous example, 1
As shown in Figure 3A, the frame (one screen) is horizontal x vertical =
It is composed of 256 pixels x 192 pixels, and one pixel is composed of 15 bits (actually 2 bytes) in which each of the three primary colors is represented by 5 bits. This original image data is then subjected to data compression processing in units of frames as follows.

That is, data for one frame of the original image is supplied to the character dividing means 22 through the input terminal 21, and as shown in FIG. 3B, each frame of image consists of 8 pixels x 8 pixels (width x height). It is divided into small area blocks (hereinafter, these blocks are referred to as characters). Therefore, as shown in FIG. 3B, one frame of image is divided into 32×24=768 characters. Then, image data C(0) to C(
767) is temporarily stored in the register 23.

The image data C(0) to C(767) of each character from this register 23 is supplied to the first vector quantization means 24. In this example as well, the vector quantization means 24 processes the image data C(0) to C(767) of each character in parallel. In this way, without parallel processing, image data C(0)
Of course, it is also possible to sequentially perform vector quantization processing on C(767). The same applies to each process described later.

In this vector quantization means 24, for each character image data C(k) (k=0 to 767),
Vector quantization is performed so that the colors appearing as pixels within the character are within four colors. In other words, as mentioned above, various proposed vector quantization methods can be used, but in this example, red,
When considering a three-dimensional color space in which the color components of the three primary colors of blue and green are orthogonal to each other, the distance between each pixel in that color space is determined, and pixels with short distances from each other are grouped together to create a color within the character. The pixel data is rounded so that the color of the pixel falls within four or less representative colors.

[0041] At this time, the color of the pixel in each character is 4.
Maximum quantization error (corresponding to the distance in the color space between the representative color and each pixel, centered on the position of the representative color) in all characters in one frame when vector quantized to fit within the color When the value is Emax, vector quantization is performed within each character until just before the quantization error exceeds Emax. This is to make the S/N of all characters within one frame uniform.

When quantized in this manner, the number of colors in a pixel is reduced for a character whose color changes are flat. This is because for characters with flat color changes, the quantization error does not increase significantly even if the number of colors decreases. In this process, some characters are created in which the number of colors in the character is three or less, two colors, or even only one color.

In this way, the vector quantization means 24 obtains pixel data compressed into four or less colors in each character. The character-by-character image data from the vector quantization means 24 is supplied to the palette division means 25.

The palette dividing means 25 classifies characters into eight groups (each group is hereinafter referred to as a palette) by grouping together characters having similar colors based on the color distribution within the character. For example, as shown in FIG. 3C, if areas with similar tones occur as A, B, C, D, E, etc. depending on the content of the image, then these areas A, B, C, D, A palette is configured for each E...

In this example, the method for allocating the eight palettes is (1) calculating the representative color of each character (the average value of the colors within the character). (2) Perform vector quantization to quantize all characters within one frame into eight colors. In other words, since the number of characters is 768, the maximum representative colors of characters are 768.
This becomes a color, but this is quantized into eight color characters. (3) Characters with the same label (representative color) are grouped together into one palette. This is done in three steps.

[0046] Note that this palette does not have to be an area of continuous characters, and characters that are separated from each other may constitute one palette.

Data of 8 pallets P(0) to P(
7) are temporarily stored in the register 26, and the second
are supplied to the vector quantization means 27 and processed in parallel.

The second vector quantization means 27 determines 16 representative colors for each palette. At this time, 1
If the number of colors in one palette is greater than 16, vector quantization is performed and the colors in the palette are rounded to 16, as in the case of characters. The resulting 16 colors are then taken as representative colors.

[0049] In this way, each of the 8 colors is rounded to 16 colors.
The image data P(0) to P(7) of the palettes are
Each is supplied to the labeling means 28 and processed in parallel. Each labeling means 28 generates color conversion tables COL(0) to COL(7) of 16 colors or 16 or less color data selected as representative colors for each palette.
is created and temporarily stored in the register 29 (see FIG. 4). And this color conversion table COL(0) ~C
The data of OL(7) is supplied to the recording processing means 38 as recording data.

Furthermore, each labeling means 28 refers to each color conversion table COL(0) to COL(7), and converts pixel data rounded to 16 colors for each character included in each palette into that palette. Label image data LAB(0) to LAB(7) in which the color of the pixel is expressed by the corresponding color number on the color conversion table
) (see Figure 5). The label image data LAB(0) to LAB(7) are then temporarily stored in the register 30.

In this case, as mentioned above, the characters may be made of four or three colors (FIG. 5A), two colors (FIG. 5B), or only one color (FIG. 5C). If the character has 4 or 3 colors, the 4 or 3
If a table indicating color numbers of colors exists, each pixel data can be represented by 2-bit data indicating which color number table it belongs to. Therefore, each pixel data of a character consisting of four or three colors can be expressed with two bits. Similarly, if the character has two colors,
The color number table for the two colors of that character, and 1 each
It can be expressed as bit pixel data. Furthermore, if there is only one color, only color data can be used.

A character that can be expressed with 2 bits is hereinafter referred to as a 2-bit mode character, a character that can be expressed with 1 bit as a 1-bit mode character, and a character that can be expressed in only one color as a monochrome character.

When considering decoding processing, 2-bit mode characters, 1-bit mode characters, and single-color characters can be processed at high speed if they are handled individually. However, among the 768 characters in one frame, each mode character generally exists dispersedly, as shown in FIG. 6A. In Figure 6, ■ is a 1-bit mode character, ■ is a 2-bit mode character,
○ indicates a monochrome character.

Therefore, the label image data LAB(0) to LAB(7) of each palette from the register 30 are as follows:
The data is supplied to the sorting means 31, and as shown in FIG. 6B, one frame of character data is rearranged in the order of 2-bit mode characters, 1-bit mode characters, and monochrome characters.

The sorting means 31 forms a screen table scr for rearranging the characters of one frame to the original order. As shown in FIG. 7, this screen table scr has a character number CNo. and pallet number PNo. is defined and constituted. Character number CNo. is the character order in one frame after sorting of the characters to be displayed at the position of the small area. Also, pallet number PNo. indicates which of the eight palettes the character displayed in that small area is included. In other words, it indicates which color conversion table to use during decoding. In this case, the character number CN of one small area
o. and pallet number PNo. is composed of, for example, 2 bytes of data.

[0056] Also, in this example, the character number CN
o. Of these, 0 to 15 are assigned only to monochrome characters. That is, in table scr, when the character displayed at the position of a certain small area is a monochrome character, the palette number PNo. is a 2-bit mode character, 1
It is assigned in the same way as the bit mode character, but the character number CNo. Instead, the color number of the character's color among the color numbers 0 to 15 in the color conversion table of the palette is assigned. Therefore, for monochromatic characters, by recording the above data in this screen table scr, they are not recorded as compressed image data for each character, which will be described later.

This screen table scr is supplied to the recording processing means 38 as recording data.

Then, as described above, the sorting means 31
Among the character-based image data sorted and rearranged in , N (N is an integer of 768 or less) each 2-bit mode character data C2(0) to C2
(N-1) is transmitted to the labeling means 3 via the register 32.
3. In this labeling means 33,
Character data C2(0) to C in each 2-bit mode
2(N-1), as shown in FIG. 8A, compressed image data consisting of a color number table of four or three colors of the character and a 2-bit index indicating the position of each color number on the color number table. dat2(0)~dat2
(N-1) is formed. Then, each compressed image data d
at2(0) to dat2(N-1) are temporarily stored in the register 34.

Similarly, from the sorting means 31, M (M is 7
Data C1(0) to C1(M-1) of each 1-bit mode character (an integer of 68 or less) are supplied to the labeling means 36 via the register 35. In this labeling means 36, for data C1(0) to C1(M-1) of each 1-bit mode character, as shown in FIG. 8B, a color number table of two colors of the character and a color number table thereof Compressed image data dat1 (0
) to dat1(M-1) are formed. Then, each compressed image data dat1(0) to dat1(M-1) is temporarily stored in the register 37.

All the 2-bit mode compressed image data from the register 34 and all the 1-bit mode compressed image data from the register 37 are each supplied to the recording processing means 38 as recording data.

The recording processing means 38 creates data to be recorded on the CD-ROM. In this example, one frame of this recorded data is processed as one block, but the CD-R
It goes without saying that the data recording mode in the OM follows the data format of the CD-ROM.

In this case, data regarding one frame of image is compressed image data regarding pixels of each character and color conversion tables COL(0) to COL(7) shown in FIG. 9 for the eight palettes of that one frame. ) and,
It is composed of the screen table scr shown in FIG.

As shown in FIG. 9, the compressed image data consists of 2
Mode number information indicating the number N of characters in bit mode and the number M of characters in 1 bit mode, and compressed image data dat2(n) of N characters in 2 bit mode (n=
0,1,2...N-1) and compressed image data dat1(m) of M 1-bit mode characters (m=0,1
, 2...M-1). As shown in the lower part of FIG. 9, the information for one character consists of a header consisting of a color number table and index data for 64 pixels. As shown in FIG. 8, the index data corresponding to each pixel is 2 bits in 2-bit mode and 1 bit in 1-bit mode. In this case, the number N of characters in the 2-bit mode and the number M of characters in the 1-bit mode change depending on the content of the pixel, so the data length of data regarding character pixels for one frame is variable.

The recording data from this recording processing means 38 is recorded on the CD-ROM, but in this case, for example, for one frame, data regarding the character pixels shown in FIG. 9 is first recorded, and then the color conversion table is recorded. COL(
0) to COL(7) and the screen table scr are recorded.

In this case, the amount of data recorded on the CD-ROM per frame is as follows.

Since there are 8 pallets per frame,
The total color conversion table is 16 (colors) x 8 (palettes) x 2 (bytes) = 256 (
part-time job). Also, since the screen table scr has 2 bytes per character, 768 x 2 (bytes) = 1536 (bytes).

[0067] In a 2-bit mode character, 4 color numbers are required to be expressed in 4 bits, so the color number table is 4 (bits) x 4 = 16 (bits) = 2 (bytes). becomes. Also, since the index is 2 bits, 2 (bits) x 64 = 128 (bits) = 16 (bytes). Therefore, one of the characters in 2-bit mode
The amount of data per character is 18 bytes. Furthermore, since a character in 1-bit mode only needs color numbers for two colors, the color number table is 4 (bits) x 2 = 8 (bits) = 1 (byte). Also, since the index is 1 bit, 1 (bit) x 64 = 64 (bit) = 8 (byte). Therefore, the amount of data per character in the 1-bit mode is 9 bytes.

For monochromatic characters, each pixel data of the character is not transmitted. Therefore, the compression ratio of one frame of image data is determined by the ratio of the number of characters in 2-bit mode and 1-bit mode to the number of monochrome characters in one frame. For example, 2 bit mode: 1 bit mode: single color = 2:1:1 =
384:192:192, color conversion table
= 25
6 byte screen table scr
= 1536 bytes Character pixel data 2-bit mode
384×18=6912 bytes
1 bit mode 192
× 9=1728 bytes total

It is 10432 bytes, which is about 10KB. 15 as the transmission rate of CD-ROM
Since 0 KB/sec is possible, in this case, a moving image of 15 frames/sec can be recorded and played back.

[0069] In addition to the compressed image information as described above, a program for decoding this compressed image information and a game program are recorded on the CD-ROM. Furthermore, audio information is also recorded as appropriate.

In the above example, after character division, each character is subjected to vector quantization, and then palette division is performed to perform the second stage processing. Even if you perform vector quantization to round the pixel colors in the palette to 16 colors, and then perform the second stage vector quantization on a character-by-character basis to compress the pixel colors in the character to 4 or less colors. good.

FIG. 10 is compressed in the above manner and becomes C.
This is an example of a device that decodes image data recorded in a D-ROM, and is applied to a game machine as described above.

That is, in FIG. 10, 41 indicates CD-
The above-mentioned information is recorded in the ROM. 42 is C
D-ROM player, 43 is a CD-ROM decoder, 4
4 is a general-purpose DSP, and 50 is a game machine. CD-RO
M player 42 plays CD-ROM 41. The played CD-ROM format data is stored in the CD-ROM.
It is decoded by the decoder 43 and converted into digital data of the compressed image information described above. The decoder processing of this compressed image data is performed by the PPU (Picture Unit) of the game machine 50.
re Processing Unit) and DSP4
4 will do it. The DSP is a programmable general-purpose DSP for audio so that it can be used for purposes other than video decoding, such as voice recognition.

Reference numeral 45 denotes a system cartridge inserted into the game machine 50. When the CD-ROM 41 is not used, a system cartridge 45 for general game software is inserted. However, CD-RO
When using the M41 as game software, this system cartridge 45 is dedicated to the game machine 50.
A program written in the CD-ROM 41 causes the game machine 50 to take in data recorded on the CD-ROM 41 and perform a so-called initialization process for executing the game.

FIG. 11 is a block diagram showing the configuration of the main parts of the game machine 50. With reference to this diagram, the decoder processing of compressed image data will be explained below.

In the game machine 50, 51 is a CPU;
2 is main memory, 53 is PPU, 54 is video RAM
, 55 and 56 are data buses. Main memory 52
Data transfer between the PPU 53 and the DSP is performed by a DMA controller (not shown). The video RAM 54 has a memory capacity for two frames, and when the first frame is displayed on the display 60,
The image data of the other frame is decoded, and when the decoding is completed, the display frame is switched. Then, the DSP 44 has a buffer R for input and output.
It is equipped with an AM and a program RAM.

The decoding process basically consists of: (1) For each character, refer to the color number table and convert the 2-bit or 1-bit index data into color conversion tables COL(0) to COL(7). First table reference step of converting bits into color number data (2) For each pixel of the character in each palette, refer to the color conversion table for that palette and convert the color number data into actual color data. It consists of three steps: a step of referring to the second table for conversion (3) and a step of rearranging the characters that have been sorted.

Of the above three steps, the first table reference is performed by the DSP 44, and the second table reference and character rearrangement are performed by the PPU 53. These decoding programs are stored in the DSP4 from the CD-ROM41.
4 and PPU53. In addition, DSP4
Since the primary table reference in 4 differs depending on the character mode, two decoding programs are prepared: one for 2-bit mode and one for 1-bit mode.

The decoding procedure is as follows.

First, data for one frame is loaded from the CD-ROM 41 into the main memory 51. Next, D
A decoding program for 2-bit mode is loaded into SP44. Then, from the main memory 52 to the DSP 44
A plurality of 2-bit mode compressed image data dat2(n), taking into account the capacity of the buffer RAM, is first transferred by DMA, and the DSP 44 performs a first table lookup on this data. When the above processing is completed in the DSP 44, each color conversion table COL(0) to COL(7
) The image data (label image data) decoded into color number data is again transferred by DMA to the main memory 52 and returned. Then, this label image data is collected from the main memory 52 during the vertical blanking period and sent to the PPU.
The data is DMA-transferred to the video RAM 54 via 53. Above main memory 52 → DSP 44 → main memory 52
→The 2-bit mode compressed image data is transferred one after another through the path of the PPU 53, and the 2-bit mode compressed image data d
First-order table lookup decoding is performed for at2(n).

2-bit mode compressed image data dat2
When the first table reference decoding process (n) is completed, the 1-bit mode decoding program is loaded into the program RAM of the DSP 44. Then, in the same manner as the 2-bit mode compressed image data, the 1-bit mode compressed image data dat1(m) is decoded by the first table reference and the video R is processed via the PPU 53.
Transfer to AM54 is performed.

[0081] In this way, when all the first table reference processing of the compressed image data in the 2-bit mode and 1-bit mode is completed, the color conversion tables COL(0) to CO are transferred from the main memory 52 to the video RAM 54 of the PPU 53.
L(7) and the screen table scr are transferred by DMA.

Then, in the PPU 53, the second color conversion table using the color conversion tables COL(0) to COL(7) is
A subsequent table lookup is performed to restore each pixel to its actual color data, and the screen table scr is used to rearrange the characters into their original order. Note that monochrome characters are directly converted into actual color data from the screen table scr. In this case, the PPU 53 can refer to the table in real time,
Character rearrangement processing can be performed, and all decoding processing ends when the color conversion table and screen table scr have been transferred to the PPU 53. Then, when the decoding of this one frame worth of data is completed, the PPU 53 switches the frame in the video RAM 54 and displays the new decoded frame on the display 60.

In this case, the main memory 52, the DSP 44
, PPU53 is performed by the DMA controller, so it does not place a burden on the CPU51. Also, DSP
While the CPU 44 is decoding the first table reference, the CPU 51 is idle and can perform other processing.

In the example of FIG. 10, a game machine and a CD
- The CD-ROM device part consisting of the ROM player, CD-ROM decoder and DSP is separate from the CD-ROM device part.
The ROM device portion can be connected to the game machine as an adapter. However, game consoles and CD-ROMs
Of course, the device portion may be integrated into a device.

In the above example, bit-compressed image data and additional data such as conversion tables are stored on a CD-ROM.
Although the compressed image data and additional data are recorded on a recording medium such as a ROM, it is also possible to transmit the compressed image data and additional data by wire or wirelessly.

[0086]

As explained above, according to the present invention, image parts having similar colors are grouped together to form one area, and a plurality of areas are formed for one screen, and image data is is divided into regions. Then, vector quantization processing is performed within the region consisting of image parts of similar colors, so that quantization errors are reduced.

Furthermore, since the decoding process can be performed simply by referring to the table, the configuration of the decoding device becomes simple. Since a large-capacity buffer memory is not required, a general-purpose DSP whose built-in buffer memory capacity is limited can be used as a decoder, and the decoder can be manufactured at low cost.

Furthermore, since compression processing is performed without using correlation between image frames, even if an error occurs during decoding,
The effect is that the error is terminated within the processing unit and does not propagate to frames of other processing units.

[0089] The existence of a recording medium on which image data that can be compressed with high efficiency and decoded using a device that is easy to decode as described above is available, making it possible to easily play back moving images from this recording medium. In particular, when a CD-ROM is used as a recording medium, practical effects such as use as software for game machines can be expected.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a portion of an example of an encoding device that implements an embodiment of an image data compression method according to the present invention.

FIG. 2 is a block diagram of the remainder of an example of an encoding device that implements an embodiment of the image data compression method according to the present invention.

FIG. 3 is a diagram for explaining an example of region division in an embodiment of the image data compression method according to the present invention.

FIG. 4 is a diagram for explaining a table used in an embodiment of the image data compression method according to the present invention.

FIG. 5 is a diagram for explaining an example of compressed data according to an embodiment of the image data compression method according to the present invention.

FIG. 6 is a diagram for explaining an embodiment of the image data compression method according to the present invention.

FIG. 7 is a diagram for explaining an example of a table used in an embodiment of the image data compression method according to the present invention.

FIG. 8 is a diagram for explaining an example of compressed image data recorded by an embodiment of the image data compression method according to the present invention.

FIG. 9 is a diagram showing an example of a data format recorded on a recording medium according to another embodiment of the image data compression method according to the present invention.

FIG. 10 is a diagram for explaining an example of a decoding system for image data compressed by the image data compression method according to the present invention.

FIG. 11 is a diagram showing an example of specific blocks of the decoding system of FIG. 10.

FIG. 12 is a block diagram of a portion of an example of an encoding device that implements an example of the image data compression method invented earlier.

FIG. 13 is a block diagram of the remainder of an example of an encoding device that implements an example of the image data compression method invented earlier.

FIG. 14 is a diagram for explaining an example of region division used in the image data compression method invented earlier.

FIG. 15 is a diagram for explaining an example of a table and compressed image data used in the image data compression method invented earlier.

FIG. 16 is a diagram for explaining an example of a table and compressed image data used in the image data compression method invented earlier.

[Explanation of symbols]

2 First area dividing means 4 Second stage vector quantizing means 11 Second area dividing means 13 Second stage vector quantizing means 22 Character dividing means 24 First stage vector quantizing means 25 Palette dividing means 27 Second Stage vector quantization means 38 Recording processing means 41 CD-ROM 42 CD-ROM player 43 CD-ROM decoder 44 DSP 50 Game machine

Claims (5)

[Claims] Claim 1: A color portion that approximates an image consisting of a plurality of pixels is divided into a plurality of regions, and the image data of each divided region is subjected to vector quantization processing to perform data compression. A recording medium in which image data obtained by compressing the number of bits per pixel and information for restoring the bit-compressed pixel data to image data having the original number of bits are recorded. 2. A color portion that approximates an image consisting of a plurality of pixels is divided into a plurality of regions, and the image data of each divided region is subjected to vector quantization processing to compress the data. An image data compression method that compresses the number of bits per bit. [Claim 3] An image consisting of a plurality of pixels is a plurality of first images.
The image is divided into small areas, and similar colors are grouped together using this first small area as a unit, so that the image is divided into a plurality of second areas.
The image data of each first small area (or second small area) is divided into small areas, vector quantization processing is performed, and first stage data compression is performed, resulting in compressed image data. is the second small area (or first small area)
Vector quantization processing is performed for each pixel, and a second stage of data compression is performed, resulting in the compressed image data with the number of bits per pixel, and the original bits from this bit-compressed pixel data. A recording medium that records information to be converted back into numerical image data. Claim 4: An image consisting of a plurality of pixels is
At the same time, the image is divided into a plurality of second small areas by dividing the image into a plurality of second small areas by grouping similar colors using this first small area as a unit, and creating an image of each first small area (or second small area). Vector quantization processing is performed on the data to perform first stage data compression, and the resulting compressed image data is subjected to vector quantization processing for each second small area (or first small area). Perform the second stage of data compression, and
An image data compression method that compresses the number of bits per pixel. [Claim 5] Claim 1 or 3 consisting of a CD-ROM.
Recording medium described.