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

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:

h

⁡

[

i

]

=

{

sin

⁡

(

x

)

x

}

×

Kaiser

⁡

(

i

,

β

)

,

i

=

0

,

1

,

…

⁢

,

T

-

1

,

⁢

x

=

i

-

T

-

1

2

T

-

1

2

×

π

×

nLobes

where, sin(x)/x is an ideal low frequency band pass function, and Kaiser(I, β) is a Kaiser window function.

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

h

⁡

[

i

]

=

[

sin

⁡

(

x

)

x

-

ES

·

Gaussian

⁡

(

x

)

]

·

Kaiser

⁡

(

i

,

β

)

,

⁢

i

=

0

,

1

,

…

⁢

,

T

-

1

,

x

=

i

-

T

-

1

2

T

-

1

2

×

π

×

nLobes

where ES is a parameter to determine a magnitude of a high frequency signal in a pass band, and Kaiser(i, β) is a Kaiser window function.

7. 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.

8. The method of claim 7 , 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.

9. The method of claim 7 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 x 1 (n) is an output signal, in accordance with Equation 1:

x 1 ,( n )=[↑ L]X ( n )= x ( n/L ); when n is a multiple of L=0; otherwise  Equation 1.

10. The method of claim 9 , 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 x 1 (n).

11. The method of claim 10 , 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, x 2 (n) is the input signal and x 3 (n) is an output signal represented as in Equation 2:

x 3 ( n )=[↓ M]X 2 ( n )= x 2 ( n/M ), when n is a multiple of M=0, otherwise  Equation 2.

12. 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.

13. 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.

14. 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 excluding carrier waves and 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.

15. The computer readable medium according to claim 14 , 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.

16. The computer readable medium according to claim 14 , 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.

17. The computer readable medium according to claim 16 , wherein a value of SmoothingAmount is set to be less than 1, and a value of nLobes is set to be less than 2.

18. The computer readable medium according to claim 16 , wherein the first filter coefficients are calculated by using an equation:

h

⁡

[

i

]

=

{

sin

⁡

(

x

)

x

}

×

Kaiser

⁡

(

i

,

β

)

,

i

=

0

,

1

,

…

⁢

,

T

-

1

,

⁢

x

=

i

-

T

-

1

2

T

-

1

2

×

π

×

nLobes

where, sin(x)/x is an ideal low frequency band pass function, and Kaiser(I, β) is a Kaiser window function.

19. The computer readable medium according to claim 18 , wherein the final filter coefficients are defined as:

h

⁡

[

i

]

=

[

sin

⁡

(

x

)

x

-

ES

·

Gaussian

⁡

(

x

)

]

·

Kaiser

⁡

(

i

,

β

)

,

⁢

i

=

0

,

1

,

…

⁢

,

T

-

1

,

x

=

i

-

T

-

1

2

T

-

1

2

×

π

×

nLobes

where ES is a parameter to determine a magnitude of a high frequency signal in a pass band, and Kaiser(i, β) is a Kaiser window function.

20. 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.

21. The apparatus according to claim 20 , 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.

22. The apparatus according to claim 21 , 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.

23. The apparatus according to claim 22 , 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.

24. The apparatus according to claim 22 , 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.

25. The apparatus according to claim 22 , 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.

26. The apparatus according to claim 25 , wherein a value of SmoothingAmount is set to be less than 1, and a value of nLobes is set to be less than 2.

27. The apparatus according to claim 22 , wherein the first filter coefficients are calculated by using an equation:

h

⁡

[

i

]

=

{

sin

⁡

(

x

)

x

}

×

Kaiser

⁡

(

i

,

β

)

,

i

=

0

,

1

,

…

⁢

,

T

-

1

,

⁢

x

=

i

-

T

-

1

2

T

-

1

2

×

π

×

nLobes

where, sin(x)/x is an ideal low frequency band pass function, and Kaiser(I, β) is a Kaiser window function.

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

h

⁡

[

i

]

=

[

sin

⁡

(

x

)

x

-

ES

·

Gaussian

⁡

(

x

)

]

·

Kaiser

⁡

(

i

,

β

)

,

⁢

i

=

0

,

1

,

…

⁢

,

T

-

1

,

x

=

i

-

T

-

1

2

T

-

1

2

×

π

×

nLobes

where ES is a parameter to determine a magnitude of a high frequency signal in a pass band, and Kaiser(i, β) is a Kaiser window function.

29. 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,

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.

30. The apparatus of claim 29 , 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.