Abstract: When a user pushes a scroll-direction key, an ECU obtains, from a memory, a division map corresponding to a division located in a direction designated by the scroll-direction key. The ECU then outputs the division map to a display controller. The display controller compresses the division map to store in a VRAM. At scrolling a displayed image, the display controller expands the compressed division map. It then outputs, to an image signal generator, only a necessary portion of the expanded division map. Thereby, the displayed image can be scrolled at high speed and easily recognizable for the user.

Abstract: An image data compressing apparatus comprises a color selecting unit, a data separating unit and a data compressing unit. The selecting unit selects an arbitrary color contained in an original map image. The separating unit separates the original image data into a modified color data and a selected position data. The compressing unit compresses these data separately from each other to improve data compression efficiency. The modified color data may be data in which a color of a background portion is made equal to a color of a road, and the background color may be a color which is most popularly used.

Abstract: When a user pushes a scroll-direction key, an ECU obtains, from a memory, a division map corresponding to a division located in a direction designated by the scroll-direction key. The ECU then outputs the division map to a display controller. The display controller compresses the division map to store in a VRAM. At scrolling a displayed image, the display controller expands the compressed division map. It then outputs, to an image signal generator, only a necessary portion of the expanded division map. Thereby, the displayed image can be scrolled at high speed and easily recognizable for the user.

Abstract: An image data compressing apparatus comprises a color selecting unit, a data separating unit and a data compressing unit. The selecting unit selects an arbitrary color contained in an original map image. The separating unit separates the original image data into a modified color data and a selected position data. The compressing unit compresses these data separately from each other to improve data compression efficiency. The modified color data may be data in which a color of a background portion is made equal to a color of a road, and the background color may be a color which is most popularly used.

Abstract: In a microwave tube of the type wherein an electron beam emitted by an electron gun is focused and caused to interact with an input high frequency wave at a high frequency circuit unit by magnetic flux generated by a permanent magnet type magnetic circuit, and the electron beam after the interaction is collected by a hollow cylindrical collector, a leakage flux generating means is provided near the entrance of the collector for generating leakage flux acting upon the electron beam. The leakage flux is produced by providing a notch for a pole piece adjacent to the collector and connected to the high frequency circuit unit or by reducing the cross-sectional area of the pole piece for magnetically saturating the pole piece itself or by keeping the pole piece in contact only with a portion of one end of the permanent magnet.