Patent ID: 7196821

Claim:
An image processing apparatus that converts image data into a specific expression format based on the dot on-off state by receiving image data representing tone values for each pixel and determining the dot on-off state for each pixel along a raster which is a row of such pixels, said image processing apparatus comprising: a raster grouping module that generates a raster group by grouping multiple rasters arranged in an entire width direction of an image; a last raster conversion module that selects the last raster at the end of said raster group, and by conducting dot on-off state determination for each pixel included in this last raster, converts the last raster into a dot row that indicates the dot on-off state; a first error diffusion module that calculates the binarization error arising in each pixel included in the last raster due to said dot on-off state determination and diffuses the error among multiple state-undetermined pixels in the vicinity of each such pixel; a first raster conversion module that selects the first raster located in the top position among the rasters in the raster group adjacent to the last raster and, by determining the dot on-off state for each pixel included in the first raster while taking into account the binarization errors diffused from the last raster among the pixels in this first raster, converts the first raster into a dot row that indicates the dot on-off state; a second error diffusion module that diffuses the binarization error occurring in each pixel included in the first raster among the state-undetermined pixels in the vicinity of each such pixel; and a remaining raster conversion module that converts the remaining raster other than the first raster of the raster group into a dot row in parallel with the conversion of the first raster into a dot row by determining the dot on-off state for each pixel in the remaining raster while taking into account the binarization errors that were diffused from the pixels that belong to the same raster group as the remaining raster and previously underwent dot on-off state determination, and wherein said first error diffusion module and said second error diffusion module are modules that store in a first error storage unit the errors that are diffused into pixels belonging to a raster group different from that containing the pixels as to which said dot on-off state determination has been conducted, and store in a second error storage unit the errors that are diffused into pixels belonging to the same raster group as the pixels as to which said dot on-off state determination has been conducted.