Method of converting resolution of video signals and apparatus using the same

• US 20050134731A1
• Filed: 11/23/2004
• Published: 06/23/2005
• Est. Priority Date: 11/24/2003
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lukin, Alexey, Lee, Hoyoung, Lee, Seongdeok, Park, Dusik, Kim, Changyeong
• Granted Patent: US 7,375,767 B2
• Time in Patent Office: Days
• US Class Current: 348/458
• CPC Class Codes: G06T 3/4007 based on interpolation, e.g. bilinear interpolation image demosaicing G06T3/4015; edge-driven or edge-based scaling G06T3/403
• CPC Class Codes: H03H 17/0282 Sinc or gaussian filters H03H17/0671 takes precedence
• CPC Class Codes: H03H 17/0657 where the output-delivery frequency is higher than the input sampling frequency, i.e. interpolation
• CPC Class Codes: H03H 17/0664 where the output-delivery frequency is lower than the input sampling frequency, i.e. decimation
• CPC Class Codes: H04N 7/0125 one of the standards being a high definition standard
• CPC Class Codes: H04N 7/0135 involving interpolation processes interpolation-based image scaling G06T3/4007; interpolation for video coding H04N19/587, H04N19/59

Abstract

A method converts a resolution of video signals, the method including: calculating up-sampling and down-sampling ratios based on a resolution of an input video signal and a desired resolution of an output video signal; calculating a number of filter tabs by multiplying the up-sampling and down-sampling ratios by a number of side lobes; calculating first filter coefficients of a same number of the filter tabs by multiplying a window function by a sinc function; calculating final filter coefficients by subtracting a result of a multiplication of a Gaussian function by a window function from the first filter coefficients, and then normalizing the final filter coefficients; and performing filtering in vertical and horizontal directions based on the final filter coefficients by modifying a sampling rate of an input video signal depending on the up-sampling and down-sampling ratios, to obtain clear video images.

Claims

1. A method of converting resolution of an input video signal, the method comprising:

calculating up-sampling and down-sampling ratios based on a resolution of the input video signal and a desired resolution of an output video signal;

calculating a number of filter tabs by multiplying up-sampling and down-sampling ratios by a number of side lobes;

calculating first filter coefficients of a same number of filter tabs by multiplying a window function by a sinc function;

calculating final filter coefficients of a filter by subtracting a result of a multiplication of a Gaussian function by the window function from the first filter coefficients, and then normalizing the final filter coefficients; and

performing filtering in vertical and horizontal directions based on the final filter coefficients by modifying a sampling rate of the input video signal depending on the up-sampling and down-sampling ratios.

2. The method according to claim 1, wherein the up-sampling and down-sampling ratios are calculated by using a greatest common measure of both a number of samples of the input video signal and a number of samples of a video signal having a desired definition.

3. The method according to claim 1, wherein the number of filter tabs is calculated by using an equation:

T=round(max{U,D}×

SmoothingAmount×

(nLobes−

1))×

2+1,

where T is the number of filter tabs, nLobes is the number of side lobes, U and D are optimal up-sampling and down-sampling ratios, and SmoothingAmount is a constant for modifying a cut-off frequency of the filter.

4. The method according to claim 3, wherein a value of SmoothingAmount is set to be less than 1, and a value of nLobes is set to be less than 2.

5. The method according to claim 3, wherein the first filter coefficients are calculated by using an equation:

6. The method according to claim 5, wherein the final filter coefficients are defined as:

26. The method of claim 1, wherein a sampling rate conversion for the input video signal comprises using an up-sampler to perform a zero insertion between pixels of the input video signal and to output an up-sampled video signal.

27. The method of claim 26, further including using an interpolation filter to perform low pass filtering for the up-sampled video signal based on a received filter coefficient, and using a down-sampler to perform down-sampling of the filtered video signal for a desired resolution.

28. The method of claim 26 wherein the up-sampler is an L-fold up-sampler that inserts (L−

1) zeros between samples of an L-fold up-sampled input video signal, wherein L is a preselected integer, x(n) is the input video signal and x₁(n) is an output signal, in accordance with Equation 1;

x₁(n)=[L]X(n)=x(n/L);

when n is a multiple of L=0;

otherwise. 

 

Equation 1

29. The method of claim 28, wherein a spectrum of the input video signal x(n) is compressed into (L−

1) spectral components with a range of −

π

˜

+π and

a first low pass filter has a cut-off frequency set at π

/L to pass only spectral components positioned in a low frequency band in a spectrum of the compressed input signal x₁(n).

30. The method of claim 29, wherein an M-fold down-sampler is a circuit from which an input signal is output without being altered only when a position of an input sample is an integer multiple of M, wherein M is a preselected integer, x₂(n) is the input signal and x₃(n) is an output signal represented as in Equation 2:

x₃(n)=[α

M]X₂(n)=x₂(n/L), when n is a multiple of M =0, otherwise. 

 

Equation 2

31. The method of claim 6, wherein definition, aliasing and ringing properties of the output video signal are controlled by controlling the parameter/control factor ES in the equation that calculates the final filter coefficients.

7. An apparatus to convert resolution of an input video signal, the apparatus comprising:

a first unit to calculate up-sampling and down-sampling ratios based on a resolution of the input video signal and a desired resolution of an output video signal;

a second unit to calculate a number of filter tabs by multiplying up-sampling and down-sampling ratios by a number of side lobes;

a third unit to calculate first filter coefficients of a same number of the filter tabs by multiplying a window function by a sinc function;

a fourth unit to calculate final filter coefficients of a filter by subtracting a result of a multiplication of a Gaussian function by a window function from the first filter coefficients, and then normalizing the final filter coefficients; and

first and second scaling filters to perform filtering in vertical and horizontal directions based on the final filter coefficients by modifying a sampling rate of the input video signal depending on the up-sampling and down-sampling ratios.

8. A computer readable medium having recorded thereon a computer readable program having computer-executable instructions for converting resolution of an input video signal, the computer instructions comprising:

calculating up-sampling and down-sampling ratios based on a resolution of the input video signal and a desired resolution of an output video signal;

calculating a number of filter tabs by multiplying up-sampling and down-sampling ratios by a number of side lobes;

calculating first filter coefficients of a same number of filter tabs by multiplying a window function by a sinc function;

calculating final filter coefficients of a filter by subtracting a result of a multiplication of a Gaussian function by the window function from the first filter coefficients, and then normalizing the final filter coefficients; and

performing filtering in vertical and horizontal directions based on the final filter coefficients by modifying a sampling rate of the input video signal depending on the up-sampling and down-sampling ratios.

9. The computer readable medium according to claim 8, wherein the up-sampling and down-sampling ratios are calculated by using a greatest common measure of both a number of samples of the input video signal and a number of samples of a video signal having a desired definition.

10. The computer readable medium according to claim 8, wherein the number of filter tabs is calculated by using an equation:

T=round(max{U,D}×

SmoothingAmount×

(nLobes−

1))×

2+1,

where T is the number of filter tabs, nLobes is the number of side lobes, U and D are optimal up-sampling and down-sampling ratios, and SmoothingAmount is a constant for modifying a cut-off frequency of the filter.

11. The computer readable medium according to claim 10, wherein a value of SmoothingAmount is set to be less than 1, and a value of nLobes is set to be less than 2.

12. The computer readable medium according to claim 10, wherein the first filter coefficients are calculated by using an equation:

13. The computer readable medium according to claim 12, wherein the final filter coefficients are defined as:

14. An apparatus to convert resolution of an input video signal, the apparatus comprising:

an input signal processing unit to divide the input video signal into vertical and horizontal direction components;

first and second multiplexers to apply the vertical and horizontal direction components to first and second scaling filters;

the first and second scaling filters to scale the vertical and horizontal direction components according to a predetermined scheme;

a third multiplexer to combine an output of the first and second scaling filters to provide a scaled output to an output signal processing unit; and

the output signal processing unit to convert the scaled output to a desired resolution.

15. The apparatus according to claim 14, wherein, in accordance with the predetermined scheme, each of the first and second scaling filters comprises a sampling conversion block that includes an interpolation filter having a filter coefficient determining unit and performs filtering based on filter coefficients input from the filter coefficient determining unit.

16. The apparatus according to claim 15, wherein the filter coefficient determining unit:

calculates up-sampling and down-sampling ratios based on a resolution of the input video signal and a desired resolution of an output video signal;

calculates a number of filter tabs by multiplying up-sampling and down-sampling ratios by a number of side lobes;

calculates first filter coefficients of a same number of filter tabs by multiplying a window function by a sinc function; and

calculates final filter coefficients of a filter by subtracting a result of a multiplication of a Gaussian function by the window function from the first filter coefficients, and then normalizing the final filter coefficients.

17. The apparatus according to claim 16, wherein the interpolation filter performs filtering in vertical and horizontal directions based on the final filter coefficients by modifying a sampling rate of the input video signal depending on the up-sampling and down-sampling ratios.

18. The apparatus according to claim 16, wherein the up-sampling and down-sampling ratios are calculated by using a greatest common measure of both a number of samples of the input video signal and a number of samples of a video signal having a desired definition.

19. The apparatus according to claim 16, wherein the number of filter tabs is calculated by using an equation:

T=round(max{U,D}×

SmoothingAmount×

(nLobes−

1))×

2+1,

where T is the number of filter tabs, nLobes is the number of side lobes, U and D are optimal up-sampling and down-sampling ratios, and SmoothingAmount is a constant for modifying a cut-off frequency of the filter.

20. The apparatus according to claim 19, wherein a value of SmoothingAmount is set to be less than 1, and a value of nLobes is set to be less than 2.

21. The apparatus according to claim 16, wherein the first filter coefficients are calculated by using an equation:

22. The apparatus according to claim 16, wherein the final filter coefficients are defined as:

23. An apparatus to convert resolution of an input video signal, the apparatus comprising:

a video signal resolution processing unit to divide the input video signal into vertical and horizontal direction components; and

a bi-level filtering system to perform filtering in vertical and horizontal directions based on final filter coefficients by modifying a sampling rate of the input video signal depending on up-sampling and down-sampling ratios.

24. The apparatus of claim 23, wherein the bi-level filtering system:

calculates up-sampling and down-sampling ratios based on a resolution of the input video signal and a desired resolution of an output video signal;

calculates a number of filter tabs by multiplying up-sampling and down-sampling ratios by a number of side lobes;

calculates first filter coefficients of a same number of the filter tabs by multiplying a window function by a sinc function;

calculates final filter coefficients of a filter by subtracting a result of a multiplication of a Gaussian function by a window function from the first filter coefficients, and then normalizing the final filter coefficients;

performs filtering in vertical and horizontal directions based on the final filter coefficients by modifying a sampling rate of an input video signal depending on the up-sampling and down-sampling ratios; and

scales a combined output from the filtering in vertical and horizontal directions and converts the scaled combined output to a desired resolution.

25. The apparatus of claim 23, wherein the bi-level filtering system comprises:

first and second multiplexers to apply the vertical and horizontal direction components to first and second scaling filters;

the first and second scaling filters to scale the vertical and horizontal direction components according to a predetermined scheme;

a third multiplexer to combine an output of the first and second scaling filters to provide a scaled output to an output signal processing unit; and

the output signal processing unit to convert the scaled output to a desired resolution.