System and process for image rescaling using adaptive interpolation kernel with sharpness and overshoot control

• US 8,587,726 B2
• Filed: 12/23/2009
• Issued: 11/19/2013
• Est. Priority Date: 12/31/2008
• Status: Expired due to Fees

• Current Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV), STMicroelectronics SA (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV), STMicroelectronics SA (STMicroelectronics NV)
• Inventors: Huang, Yong, Hui, Lucas, Wang, Haiyun, Lebowsky, Fritz
• Primary Examiner(s): Harold, Jefferey
• Assistant Examiner(s): SATTI, HUMAM M
• Application Number:
  US12/655,254
• Publication Number:
  US 20100165204A1
• Time in Patent Office: 1,427 Days
• Field of Search: 348/450, 348/452, 348/571, 348/580, 348/581, 348/576, 348/578, 348/606, 348/607, 382/266
• US Class Current: 348/581
• CPC Class Codes: G06T 2200/12 involving antialiasing
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• 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: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06T 5/73 Deblurring; Sharpening

Abstract

Provided are a digital video rescaling system, a method of rescaling video images, and a chip comprising a computer executable medium embedded therein computer executable instructions for rescaling video images.

Claims

1. A digital video rescaling system, comprising:

an input module configured to receive input image data;

a noise level estimator configured to estimate a noise level within a portion of the received input image data;

a local gradient estimator configured to estimate a local gradient magnitude based on the portion of the received input image data;

an overshoot control configured to generate an artifact control parameter to reduce artifacts in edge areas of an image corresponding to the received input image data;

an interpolation phase calculator configured to calculate a phase value of a pixel within the received input image data to be interpolated;

an adaptive spline interpolation kernel coupled to the input module by the interpolation phase calculator and coupled to the overshoot control, wherein the adaptive spline interpolation kernel is configured to receive the phase value, the artifact control parameter, and a global sharpness control parameter and to generate an interpolated pixel by applying a function involving the global sharpness control parameter directly on a plurality of support pixels from the input image data; and

a local sharpness control module configured to modify the global sharpness control parameter according to the estimated noise level and the estimated local gradient magnitude for the portion of the received input image data.

2. The digital video rescaling system of claim 1, wherein the adaptive spline interpolation kernel is configured to generate an interpolated pixel y₁(x) based on the following equation:

3. The digital video resealing system of claim 2, further comprising an overshoot control module coupled to the adaptive spline interpolation kernel, wherein the overshoot control module is configured to generate an overshoot control parameter to control the adaptive spline interpolation kernel, wherein the adaptive spline interpolation kernel comprises:

a max-min calculation unit configured to receive the data of pixels y_B and y_C, and configured to calculate the maximum value and the minimum value of the support pixels y_B and y_C;

a comparator coupled to the max-min calculation unit and adaptive spline interpolation kernel, wherein the comparator is configured to compare the maximum value and the minimum value of the support pixels y_B and y_C with the interpolated pixel y₁(x) to generate an output y₂(x) according the following equation;

4. The digital video rescaling system of claim 1, wherein the local sharpness control module is configured to modify the global sharpness control parameter using a transfer function based on the local gradient magnitude and the noise level.

5. The digital video resealing system of claim 4, wherein the transfer function of the local sharpness control parameter function module can be expressed as:

Kshp(Gn)=AKshp(Gn)+GKshp,

wherein GKshp is a fixed value that is defined by a global sharpness control parameter Kshp, AKshp(Gn) is a variable value that is defined by control parameters max K, min K, K1, K2, K3, and Sigma, wherein Sigma is the noise level, wherein Gn is a local gradient magnitude; and

wherein AKshp(Gn) is expressed by a transfer function according to the following equation;

6. The digital video resealing system of claim 1, further comprising an anti-aliasing filter coupled between the input module and the adaptive spline interpolation kernel, wherein the anti-aliasing filter comprises a set of low pass filters that are configured to reduce aliasing artifacts during image downscaling.

7. The digital video rescaling system of claim 6, further comprising a switch device coupled between the input module and the anti-aliasing filter, wherein the switch device is configured to activate the anti-aliasing filter during downscaling, and wherein the switch device is configured to deactivate the anti-aliasing filter during upscaling.

8. A method of rescaling video images, comprising:

receiving data corresponding to an input image;

estimating a noise level within a portion of the received input image data and a local gradient magnitude based on the portion of the received input image data;

generating an artifact control parameter to reduce artifacts in edge areas of an image corresponding to the received input image data;

calculating a phase value of a pixel within the received input image data to be interpolated;

modifying a global sharpness control parameter according to the estimated noise level and the estimated local gradient magnitude for the portion of the received input image data; and

calculating interpolated pixel values based on the phase value and the artifact control parameter and by applying a function involving the global sharpness control parameter directly on the input image data by using an adaptive spline interpolation kernel.

9. The method of claim 8, wherein the adaptive spline interpolation kernel is configured to generate an interpolated pixel y₁(x) based on the following equation:

10. The method of claim 9, wherein calculating interpolated pixel values comprises:

calculating a maximum value and a minimum value of the support pixels y_B and y_C;

comparing the maximum value and the minimum value of the support pixels y_B and y_C with the interpolated pixel y₁(x) to generate an output y₂(x) according the following equation;

11. The method of claim 8, further comprising modifying the global sharpness control parameter by using a transfer function based on the local gradient magnitude and the noise level.

12. The method of claim 11, wherein the transfer function can be expressed as:

Kshp(Gn)=AKshp(Gn)+GKshp,

wherein GKshp is a fixed value that is defined by a global sharpness control parameter Kshp, AKshp(Gn) is a variable value that is defined by control parameters max K, min K, K1, K2, K3, and Sigma, wherein Sigma is the noise level, wherein Gn is a local gradient magnitude, and

wherein AKshp(Gn) is expressed by a transfer function according to the following equation;

13. The method of claim 8, further comprising:

selecting a set of filter coefficients from a low pass filter bank according to a downscaling factor; and

applying the set of filter coefficients on the input image data to reduce anti-aliasing effects during downscaling.

14. A chip comprising a computer executable medium embedded therein computer executable instructions for rescaling video images, wherein the instructions comprise instructions for:

receiving data corresponding to an input image;

estimating a noise level within a portion of the received input image data and a local gradient magnitude based on the portion of the received input image data;

generating an artifact control parameter to reduce artifacts in edge areas of an image corresponding to the received input image data;

calculating a phase value of a pixel within the received input image data to be interpolated;

modifying a global sharpness control parameter according to the estimated noise level and the estimated local gradient magnitude for the portion of the received input image data; and

calculating interpolated pixel values based on the phase value and the artifact control parameter and by applying a function involving the global sharpness control parameter directly on the input image data by using an adaptive spline interpolation kernel.

15. The chip of claim 14, wherein the adaptive spline interpolation kernel is configured to generate an interpolated pixel y₁(x) based on the following equation:

16. The chip of claim 15, wherein calculating interpolated pixel values comprises:

calculating a maximum value and a minimum value of the support pixels y_B and y_C;

comparing the maximum value and the minimum value of the support pixels y_B and y_C with the interpolated pixel y₁(x) to generate an output y₂(x) according the following equation;

17. The chip of claim 14, wherein modifying the global sharpness control parameter comprises:

modifying the global sharpness control parameter by using a transfer function based on the local gradient magnitude and the noise level.

18. The chip of claim 17, wherein the transfer function can be expressed as:

Kshp(Gn)=AKshp(Gn)+GKshp,

wherein GKshp is a fixed value that is defined by a global sharpness control parameter Kshp, AKshp(Gn) is a variable value that is defined by control parameters max K, min K, K1, K2, K3, and Sigma, wherein Sigma is the noise level, wherein Gn is a local gradient magnitude, and

wherein AKshp(Gn) is expressed by a transfer function according to the following equation;

19. The chip of claim 14, wherein the instructions further comprise instructions for:

selecting a set of filter coefficients from a low pass filter bank according to a downscaling factor; and

applying the set of filter coefficients on the input image data to reduce anti-aliasing effects during downscaling.

20. The chip of claim 19, wherein the instructions further comprise instructions for:

deactivating the set of filter coefficients on the input image data during upscaling.