The present invention relates to an image processing system, and more particularly to a game computer system processing a variety of images such as a natural picture together with an animation picture.
In a conventional game computer system, image data are defined by color for each dot. The colors of the image data are managed by a color pallet formed in a memory, the color pallet storing many pallet codes (PLT) corresponding to color data.
In the conventional game computer system, image data are compressed (encoded) to be transmitted, and then the compressed data are extended (decoded) to be displayed. Each piece of image data is composed of the pallet code (PLT) and the number (CRL) thereof, which is called a pallet length. The compression method is called a "run-length" method.
When a single color mode is employed for each screen, image data may be fixed in length (bits); however, when plural color modes are used for one screen, the lengths of the image data are different depending on the color mode.
FIG. 1 shows the formats of image data according to the conventional game computer system, which employs 16, 32, 64 and 128 color modes. The pallet codes are defined by data of 4, 5, 6, and 7 bits for the 16, 32, 64 and 128 color modes, respectively. The length "L" of the pallet code in a color mode "m" is given by the following equation. EQU L=log.sub.2 m
For example, the length "L" of the pallet code in the 128 color mode becomes "7" as follows: EQU L=log.sub.2 128=log.sub.2 2.sup.7 =7
The data needs to have a width corresponding to a bus line to be transmitted thereon, because the widths of buses vary depending on the system.
When the image data are transmitted on a 8 bit bus, the data for the 16 color mode may be transmitted in entirely, as shown in FIG. 1; however, when the length of the image data to be transmitted is not a multiple of 8 bits, the data need to be divided, as shown in FIG. 2. For example, image data for the 32 color mode are compressed to 9 bits, the data are divided as 8 and 1 to be transmitted, and as a result, the left over one bit is transmitted with the following data.
In the conventional game computer system, when the screen is divided into plural areas of different colors, the color mode of the greatest number is selected, because each picture is displayed using only one color mode. For example, when an animation picture with 16 colors and a natural picture with 16M colors are synthesized on the screen, the synthesized picture is displayed in the 16M color mode. Such a processing method is not effective for using the memory.