Methods and apparatus for re-scaling image by variable re-scaling factor

• US 7,542,053 B2
• Filed: 03/30/2005
• Issued: 06/02/2009
• Est. Priority Date: 03/30/2005
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Berenguer, Inaki, Kurupati, Sreenath, Hormis, Raju
• Primary Examiner(s): WANG, JIN CHENG
• Application Number:
  US11/093,674
• Publication Number:
  US 20060227152A1
• Time in Patent Office: 1,525 Days
• Field of Search: 382/298, 345/698, 345660-661, 348/581
• US Class Current: 345/660
• CPC Class Codes: G06T 3/4084 in the transform domain, e.g. fast Fourier transform [FFT] domain scaling

Abstract

A method includes receiving a sequence of samples that represents a row of pixels in an image. The method further includes selecting a re-scaling factor for at least a portion of the row of pixels. The method further includes selecting a filter from a bank of low pass filters based on the selected re-scaling factor, and low-pass filtering the sequence of samples with the selected filter. The method further includes up-sampling the low-pass-filtered sequence of samples by a factor M with a polyphase filter bank having a windowed sinc(t) characteristic to the up-sampled sequence of samples, and down-sampling the polyphase-filtered sequence of samples.

Claims

1. A method for re-scaling image by variable re-scaling factor, the method comprising:

receiving by a re-scaling circuit a sequence of samples that represents a row of pixels in an image;

selecting a re-scaling factor for at least a portion of said row of pixels;

selecting a filter from a bank of low pass filters in the re-scaling circuit based on the selected re-scaling factor;

low-pass filtering the sequence of samples with the selected filter;

upsampling the low-pass filtered sequence of samples by a factor M with a polyphase filter bank in the re-scaling circuit having a windowed sinc(t) characteristic, M being a positive integer; and

down-sampling with a down-sampling block in the re-scaling circuit the polyphase-filtered sequence of samples by a factor N, N being an integer selected such that M/N is substantially equal to the selected re-scaling factor;

wherein the re-scaling factor varies depending on a current position along said row of pixels;

wherein said upsampling with the polyphase filter bank includes;

implementing the polyphase filter bank with a table that comprises a plurality of rows and a plurality of columns;

setting a first variable to equal an inverse of a currently selected scaling factor;

initializing a second variable; and

at each pixel location in said row of pixels;

setting a main tap of the polyphase filter bank at an index indicated by an integer portion of the second variable;

setting a third variable to equal a non-integer portion of the second variable;

selecting a row from said table in accordance with a value of the third variable;

filtering the sequence of samples by a phase of the polyphase filter bank which corresponds to the selected row from said table; and

increasing a value of the second variable by a value of the first variable.

2. The method of claim 1, wherein N>

M.

3. The method of claim 1, wherein M>

N.

4. A method for re-scaling image by variable re-scaling factor, the method comprising:

receiving by a re-scaling circuit a sequence of samples that represents a row of pixels in an image;

selecting a re-scaling factor for at least a portion of said row of pixels;

upsampling the sequence of samples by a factor M with a polyphase filter bank in the re-scaling circuit having a windowed sinc(t) characteristic, M being a positive integer;

selecting a filter from a bank of low pass filters in the re-scaling circuit based on the selected re-scaling factor;

low-pass filtering the polyphase-filtered sequence of samples with the selected filter from said bank of low pass filters; and

down-sampling with a down-sampling block in the re-scaling circuit the low-pass-filtered sequence of samples by a factor N, N being an integer selected such that M/N is substantially equal to the selected re-scaling factor;

wherein the re-scaling factor varies depending on a current position along said row of pixels;

wherein said upsampling with the polyphase filter bank includes;

implementing the polyphase filter bank with a table that comprises a plurality of rows and a plurality of columns;

setting a first variable to equal an inverse of a currently selected scaling factor;

initializing a second variable; and

at each pixel location in said row of pixels;

setting a main tap of the polyphase filter bank at an index indicated by an integer portion of the second variable;

setting a third variable to equal a non-integer portion of the second variable;

selecting a row from said table in accordance with a value of the third variable;

filtering the sequence of samples by a phase of the polyphase filter bank which corresponds to the selected row from said table; and

increasing a value of the second variable by a value of the first variable.

5. The method of claim 4, wherein N>

M.

6. The method of claim 4, wherein M>

N.

7. A method for re-scaling image by variable re-scaling factor, the method comprising:

receiving by a re-scaling circuit a sequence of samples that represents a row of pixels in an image;

selecting a re-scaling factor for at least a portion of said row of pixels;

upsampling the sequence of samples by a factor M with a polyphase filter bank in the re-scaling circuit having a windowed sinc(t) characteristic, M being a positive integer;

down-sampling with a first down-sampling block in the re-scaling circuit the polyphase-filtered sequence of samples by a factor N₁, N₁ being an integer;

low-pass filtering the down-sampled sequence of samples with a bank of low pass filters in the re-scaling circuit; and

down-sapling with a second down-sampling block in the re-scaling circuit the low-pass-filtered sequence of samples by a factor N₂, N₂ being an integer;

wherein N₂ is selected such that M/(N₁*N₂) is substantially equal to the selected re-scaling factor; and

wherein the re-scaling factor varies depending on a current position along said row of pixels;

wherein said upsampling with the polyphase filter bank includes;

implementing the polyphase filter bank with a table that comprises a plurality of rows and a plurality of columns;

setting a first variable to equal an inverse of a currently selected scaling factor;

initializing a second variable; and

at each pixel location in said row of pixels;

setting a main tap of the polyphase filter bank at an index indicated by an integer portion of the second variable;

setting a third variable to equal a non-integer portion of the second variable;

selecting a row from said table in accordance with a value of the third variable;

filtering the sequence of samples by a phase of the polyphase filter bank which corresponds to the selected row from said table; and

increasing a value of the second variable by a value of the first variable.

8. A method for re-scaling image by variable re-scaling factor, the method comprising:

storing a plurality of sets of coefficients in a table in a re-scaling circuit, each set of coefficients representing a polynomial approximation of a respective interval of a windowed sinc(t) function;

receiving by the re-scaling circuit a sequence of samples that represents a row of pixels in an image;

selecting a re-scaling factor for at least a portion of said row of pixels;

setting a first variable to equal an inverse of an integral multiple of the selected re-scaling factor;

initializing a second variable;

at each pixel location in said row of pixels;

setting a main tap of a filter at an index indicated by an integer portion of the second variable;

setting a third variable to equal a non-integer portion of the second variable;

evaluating each of said polynomial approximations at a point along a curve segment to generate filter coefficients to define said filter, said curve segment corresponding to said each polynomial approximation, said point along said curve segment corresponding to a value of said third variable;

applying said filter to selected samples from said sequence of samples to generate an output pixel value; and

increasing a value of the second variable by a value of the first variable.

9. The method of claim 8, wherein said re-scaling factor varies depending on a current position along said row of pixels.

10. The method of claim 8, wherein each of said polynomial approximations is a third order polynomial.

11. A system for re-scaling image by variable re-scaling factor, the system comprising:

a bank of low pass filters in a re-scaling circuit to receive a sequence of samples that represents a row of pixels in an image;

a re-scaling factor block in the re-scaling circuit to select a re-scaling factor for at least a portion of said row of pixels and to select a filter from said bank of low pass filters based on the selected re-scaling factor, said selected filter to low pass filter the sequence of samples;

a polyphase filter bank in the re-scaling circuit coupled downstream from the bank of low pass filters to filter the low-pass filtered sequence of samples and to upsample the low-pass filtered sequence of samples by a factor M, M being a positive integer, the polyphase filter bank having a windowed sinc(t) characteristic; and

a down-sample block in the re-scaling circuit coupled downstream from the polyphase filter bank and also coupled to the re-scaling factor block, to down-sample the sequence of samples filtered by the polyphase filter bank, the down-sampling by a factor N selected by the re-scaling factor block, N being an integer selected such that M/N is substantially equal to the selected re-scaling factor;

wherein the re-scaling factor block is operative to vary the re-scaling factor depending on a current position along said row of pixels;

wherein said bank of low pass filters includes at least three low pass filters, each having a respective cut-off frequency that is different from the cut-off frequency of the other low pass filters of the bank of low pass filters.

12. The system of claim 11, wherein the bank of low pass filters, the re-scaling factor block, the polyphase filter bank and the down-sample block are included in a video-processing integrated circuit (IC), the system further comprising a graphics memory unit in communication with the video-processing IC.