Abstract: A gradation image output apparatus in which processing speed does not decrease when binary image data is output and having a reduced memory capacity of the multi-bit bit-map planes. The image output apparatus includes both multi-bit gradation image storage and 1-bit gradation image storage. The multi-bit gradation image storage stores an image, each pixel of which has multi-bit data representing gradation level of the pixel. The 1-bit gradation image storage stores image data, each pixel of which is in one of two different gradation levels in which a gradation level of an area composed of a plurality of the pixels is represented by a ratio of pixels of one state to the other. The image output apparatus expands image data and synthesizes the expanded image data in both the multi-bit gradation image storage and the 1-bit gradation image storage.

Abstract: A method and apparatus for managing color data in a predetermined color space by using a pallet converting mechanism, in which a pallet management table can be efficiently registered and updated. An entry number accessing a table entry in the pallet management table is formed by combining the components of the color data. Table data, obtained by combining remaining components of the color data which are not used for the formation of the entry number, is stored into the table entry identified by the entry number. There is also the conversion of color data to pallet data, which corresponds to entry numbers, and the reverse conversion to reconstruct the original color data from pallet data and entry number information. Validity information indicative of the validity of the table entry is also registered into the table entry of the pallet management table, so that an available table entry at the time of new registration can be immediately found out.