Sample rate converter circuit for image data

• US 5,274,469 A
• Filed: 12/23/1991
• Issued: 12/28/1993
• Est. Priority Date: 12/23/1991
• Status: Expired due to Fees

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Uebelacker, John J., Small, Jeffrey A.
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): LEE, TOMMY D
• Application Number:
  US07/810,405
• Time in Patent Office: 736 Days
• Field of Search: 358/443, 358/445, 358/448, 358/425, 358/426, 358/133, 358/138, 341/61, 341/123
• US Class Current: 358/445
• CPC Class Codes: G06T 3/40 Scaling of whole images or parts thereof, e.g. expanding or contracting
• CPC Class Codes: H03H 17/0621 with input-sampling frequency and output-delivery frequency which differ, e.g. extrapolation; Anti-aliasing

Abstract

The present invention is a sample rate converter in which a weighted filtering operation is performed. This operation stores a pixel stream in a random access memory (RAM) 30. During conversion pointers stored in counter 38 and register 40 are used to select the pixels from the RAM which are then multiplied by filter weights and accumulated. A counter 44 and mapping unit 46 select the weight being multiplied. The multiplication is performed by a lookup table read only memory (ROM) 32 that stores the results of the pixel-weight multiplication for all combinations of pixels and weights for each sample rate. An accumulator 33 stores the results of the multiplication until all multiplications have occurred at which point the filtered pixel is output. The output of the lookup table 32 is controlled by the pixel value, the coefficient selected and the table or map selected. The lookup table stores symmetric weights for as many conversion rates as desired. The mapping unit 46 maps a sequential coefficient count to a coefficient identifier which is non-sequential and symmetric allowing the size of ROM 32 to minimized and the number of address lines provided to the ROM 32 to be minimized.

Claims

1. A sample rate converter comprising:

storage means including a random access memory for storing input data at a first sample rate,

convolution filter means for directly filtering the input data to produce output data at a second sampling rate, wherein said filter means includes;

a filter coefficient storage outputting filter coefficients corresponding to the input data and for each sample conversion rate, and

a multiplier connected to said storage means and multiplying the input data times the filter coefficients;

an accumulator connected to said multiplier and accumulating the coefficient multiplied input data, and

multiplication storage means connected to said memory for storing all combinations of pixel values time filter coefficients for each sample conversion rate, and

an accumulator connected to said storage means, further comprising a control unit connected to said memory and said filter means, said control unit includes;

a multiplexer selecting between memory pointers for said memory;

first and second pointer counters connected to said multiplexer;

a third pointer counter connected to said multiplication storage; and

a control unit connected to said storage means, said filter means and said pointer counters.

2. A converter as recited in claim 1, further comprising mapping means, connected between said third pointer counter and said multiplication storage, for converting a sequential count to a non-sequential coefficient selection.

3. A converter as recited in claim 2, wherein said mapping means converts a sequential count, a coefficient subset selection and a sample rate conversion map selection into the non-sequential coefficient selection.

4. A converter as recited in claim 3, wherein said mapping means comprises one of a ROM look-up table and decode logic.

5. A converter as recited in claim 1, wherein filter coefficients are symmetric and said multiplication storage comprises a memory divided into tables corresponding to sample rate conversions and each table being divided into coefficient sections storing the pixel values times a corresponding symmetric filter coefficient.

6. A sample rate converter for converting input pixel values input at a first rate to output pixel values produced at a second rate, said converter comprising:

a random access memory storing the input data;

a multiplexer connected to said random access memory;

a first counter connected to said multiplexer and controlling storage of the input pixel values into said random access memory;

a register connected to said multiplexer and controlling output of the input pixel values to produce the output pixel values;

a read only memory connected to said random access memory and storing pixel values times filter coefficient values;

a mapping unit connected to said read only memory and producing a coefficient selection value;

a counter connected to said mapping unit and controlling production of the coefficient selection value; and

an accumulator connected to said read only memory and producing the output pixel values.