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Shift Register Implemented Image Rotator Transposer

IP.com Disclosure Number: IPCOM000083036D
Original Publication Date: 1975-Mar-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Gold, DE: AUTHOR

Abstract

Described is an apparatus and method by means of which an n by n point array may be rotated by 90 degrees or transposed through the use of n shift registers, each of length n. A small amount of additional switching and control logic is required in conjunction with the shift registers. The total hardware required should be less expensive than a random-access memory used for the same purpose. This is because the device described here may be realized by cheaper devices than random-access memories.

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Shift Register Implemented Image Rotator Transposer

Described is an apparatus and method by means of which an n by n point array may be rotated by 90 degrees or transposed through the use of n shift registers, each of length n. A small amount of additional switching and control logic is required in conjunction with the shift registers. The total hardware required should be less expensive than a random-access memory used for the same purpose. This is because the device described here may be realized by cheaper devices than random-access memories.

A shift register is defined as a recirculating storage unit of m cells, each of which may contain a datum. A datum will be the bit representation of a single picture element (pel) in an image, frequently referred to as "pel" when unambiguous. The shift registers, or more simply, register, has a "port" which is a unique location at which the contents of a cell may be read or written.

Numbers 1 to m to denote m distinct data items contained in the register are shown in Fig. 1a. The register may be "cycled" which has the effect bringing the next cell to the port and moving the cell last there to the end. Fig. 1b shows the register of Fig. 1a after having been cycled once. A register may only shift in a single direction, as shown by the arrows

The contents of the cell at the port may be read or (over)written but a cycle is required to do so, thus placing that cell at the end of the register immediately after the read or write operation. Since the contents of a cell may only be read when that cell is at the port, in general some number of cycles is required to access a given cell in a register. This is precisely the disadvantage of shift register memories over random-access memories, and shown here is a method which makes use of shift registers while still providing for minimal access times. This is done by insuring that the desired data are at their respective ports for reading at the appropriate times.

The image is described as an n by n array of pels and will assume a left-to- right, top-to-bottom sequence. Thus, if each pel transmitted is identified by its number in sequence, an image is depicted as in Fig. 2. A 90-degree clockwise rotation of the image in Fig. 2 is shown in Fig. 3. The transformation from Fig. 2 to Fig. 3 is a (clockwise) 90-degree rotation.

Each scan line of the image is routed to its unique register by a router or switch. (See Fig. 4). Thus,...