Xerox Corporation

Robert E Coward

James D Parker

Louis D Mailloux

Henry R Kang

An image processing apparatus in a reproduction system includes an image input terminal having a device resolution of K pixels per unit length by L pixels per unit length (K x L). Each pixel is defined at a depth b representing one of b optical densities. The image input terminal emits an input image at the device resolution and depth (KxLxb). A memory is provided for receiving and storing as electrical signals the input image emitted from the image input terminal. A first processing means converts the resolution of the input image to a plurality of output images at a second resolution of M pixels per unit length by N pixels per unit length (M x N). Each pixel is defined at depth d representing one of d optical densities. The first processing means converts the input image to the plurality of output images by spatially offsetting a periodically repeating mapping defining the conversion between the input image and the output image. A second processing means forms a distribution of the plurality of output images. The second processing means selects a composite output image from the distribution of output images and stores the composite output image in the memory. An image output terminal having a device resolution and depth of M x N x d, is adapted for reproducing the composite image stored in the memory.

Image resolution conversion using a plurality of image registrations

In a method for converting from a first bitmap image resolution to a second bitmap resolution, be it interpolation (an increase in resolution) or decimation (a decrease in resolution) a bitmap image defined at resolution and density I.times.J.times.a is prefiltered as a first step to ensure the preservation of original image structure and compensate for device dependence of the input image, which is necessary in order to maintain the quality and sharpness of the original image. The filter may be selected from a variety of filter choices and may also perform pixel interpolation or decimation depending on the input source. As a second step, unquantized scaling of a prefiltered image (K.times.L.times.b) is performed using an f.times.g pixel window to identify a set of neighboring input pixels surrounding a single output pixel. The window contributes input pixel density information to generate a scaled gray output pixel. Each pixel in the window is assigned a weighting factor to establish a density contribution to the output pixel. As a third step, each pixel in the gray scale image (M.times.N.times.c) is quantized to a desired depth using error diffusion or other quantizing methods. The gray scale image is converted from an image defined at c levels to an output image defined at d levels where each of the d levels can be reproduced by a selected output device.

Unquantized resolution conversion of bitmap images using error diffusion

A method for converting a set of input image pixels having a first resolution and being represented by a set of input image signals to a set of output image pixels having a second resolution and being represented by a set of output image signals. The method is adapted for use in an electroreprographic machine having a memory for storing images and an image output terminal for printing the images. The method comprises the following steps: first, developing a set of state determination rules which govern the conversion of the set of input image pixels having the first resolution to the set of output image pixels having the second resolution; second, communicating the set of input image signals and the set output image signals to the memory, third, relating a plurality of selected input image pixels with a selected one of the output image pixels; fourth, determining respective binary states of the plurality of selected input image pixels; finally, corresponding the selected output image pixel with one of at least three output states by reference to the determined, respective binary states and one of the state determination rules.

Resolution conversion with simulated multi-bit gray

A method for converting binary image data originally generated at a lower resolution into representative binary image data of a higher resolution, wherein the conversion ratio, or magnification factor, is an integer value. Also included are methods for smoothing the interpolated output image and thereby reducing objectionable visual characteristics observable in digitally encoded data using conventional magnification techniques.

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Rochester, NY, United States of America

Robert E Coward