Apple Inc.

Magnus L Karlsson

Kok S Chen

Hungviet H Nguyen

Allen M Chan

Marilyn Chen

Chi-Shing J Ng

A method and apparatus for halftoning where at most one halftoned gray, or multi-level, pixel will occur in those halftone cells having a constant area of ink. The method and apparatus includes placing a threshold array and the pixel tonal values within the same range if the threshold array and pixel tonal values are in different ranges. The elements in the threshold array are then compared to the pixel tonal values in order to determine a resulting output value. The preferred apparatus for halftoning includes a memory for storing the threshold array; a multiplier for multiplying one 8-bit value representing the number of pixels in a halftone cell by a second 8-bit value which is a pixel tonal value; a comparator for comparing the results of the multiplier with an element from the threshold array; and a multiplexer for selecting a resulting output value based upon the output generated by the comparator.

Method and apparatus for color halftoning

A system for accelerated data recompression in which uncompressed data need not be swapped in and out of memory at each iterative data recompression step. The data recompression system includes a main memory for storing image data, and a decompression device which receives compressed data from the main memory and decompresses it to produce discrete blocks of uncompressed data. An intermediate compression buffer, separate from the main memory and connected to the decompression device, is used by the decompression device to store one block of uncompressed data at a time. The blocks of data are received one at a time by a data compression device taking input directly from the intermediate compression buffer. There the uncompressed data blocks are compressed and stored back to the main memory one block at a time. Thus, an entire compressed image stored in main memory is decompressed and recompressed one block at a time, and uncompressed data need not be swapped in and out of main memory. As a result, overall data recompression speed is greatly improved.

System and method for accelerated data recompression

The present invention is directed to systems and methods for compressing image data without segregating the image data into scanned and non-scanned components, while at the same time, improving both the compression ratio and the perceptabilty of the decompressed image. Improved perceptibility is realized regardless of whether the image data includes scanned images, non-scanned images or any combination thereof. Further, improved perceptibility is realized regardless of whether the images are monochrome or color.

Method and apparatus for compression of digitized image data using

A system and method for halftoning multi-level pixels preferably uses a threshold array divided into two or more classes. The classes are ordered in a visitation order. Each class contains at least one element. A halftone cell comprised of a plurality of pixels corresponds to the threshold array. As the intensity level for the halftone cell increases, the pixels corresponding to the elements in the first class are halftoned by fractional values of pixels until all of the pixels in that class reach saturation. As the intensity of the halftone cell increases, none of the pixels corresponding to the elements in any other class change state. Once the pixels corresponding to the elements in the first class are saturated, the pixels corresponding to the elements in the second class are halftoned by fractional values of pixels. In more general terms, the next class in the class visitation order is not addressed until the pixels corresponding to all of the elements in the previous class are saturated.

Method and system for halftoning

A multi-level image output device performs correction of pixel values which have undergone halftone processing to compensate for non-linearities. This correction is carried out by means of a tonal reproduction transfer function, which linearizes the output values from a halftone processor before they are applied to an image generator, such as a laser modulator. By rectifying non-linear intensity of individual pixels, images can be generated with a smoother grayscale gradient. The function of the post-halftone correction can be combined with a modulator, to achieve an economy of components which make up the output device. As a further feature, a plurality of post-halftoning correction devices can be provided. One of these devices is selected to correct the data values produced by halftone processing, in dependence upon the values of neighboring pixels in an image.

Tone correction for multi-level halftoned images

A programmable interrupt delay in a communication circuit enables accurate timing of an interrupt delay without tying up processor CPU cycles in the execution of a delay loop. The interrupt delay comprises a memory containing the program delay value. A communication circuit which generates an interrupt output corresponding to the transmission of a communication data stream is coupled to a timing circuit having a time value. This timing circuit also has a timing start input, which triggers timing of the timing value upon receipt of the interrupt output. A comparator coupled to the memory and to the timing circuit compares the time value to the delay value and generates a delayed interrupt when the time value and the delay value are equal.

Programmable delay of an interrupt

The system and method disclosed herein relates to digital halftoning where a threshold array is used to control individual pixels in a halftone cell. The threshold array is replicated to tile the entire device space so that each pixel in device space is mapped to a particular location in the threshold array. By tiling the threshold array with overlap, the size of the overall threshold array is reduced. A CPU interface couples a FIFO buffer, registers, and RAM to a CPU for receiving pixel data, control signals and other values, respectively. An engine control unit is coupled to control a video processing unit and an output device for producing halftone images with a halftone matrix of reduced size. The engine control unit controls threshold logic that applies the threshold matrix to the pixel data to produce the data stream sent to the output device. The method of the present invention preferably comprises the steps of: defining a halftone cell and a minimal threshold array; mapping the threshold array over device space; determining a row and a column in the threshold array for the previous pixel of the image that has been rendered to device space; determining whether the next pixel is vertically adjacent or horizontally adjacent to the pixel that was previously mapped to device space; determining whether the next pixel is within the threshold array used for the previous pixel; and adjusting the mapping to account for overlapping threshold arrays if the next pixel is not within the threshold array used for the previous pixel.

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Milpitas, CA, United States of America

Magnus L Karlsson