Method of Image Scaling

• US 20090122084A1
• Filed: 10/24/2008
• Published: 05/14/2009
• Est. Priority Date: 11/14/2007
• Status: Active Grant

• Current Assignee: BYD Semiconductor Co., Ltd.
• Original Assignee: BYD Company Limited
• Inventors: Zhu, Ruohong, Yu, Zhilong
• Granted Patent: US 8,068,122 B2
• Time in Patent Office: Days
• US Class Current: 345/660
• 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

Abstract

A method of image scaling includes the steps of: determining the coordinates of a virtual pixel in an original image, wherein the virtual pixel corresponds to an actual pixel in a scaled image; determining the coordinates of four actual pixels in the original image that are closest to the virtual pixel; determining the weights of the four actual pixels; and determining the pixel value of the virtual pixel in the original image in accordance with the determined weights and the pixel values of the four actual pixels.

Claims

1. A method of image scaling, comprising:

determining the coordinates of a virtual pixel in an original image, wherein the virtual pixel corresponds to an actual pixel in a scaled target image;

determining the coordinates of four actual pixels in the original image that are closest to the virtual pixel;

determining the weights of the four actual pixels; and

determining the pixel value of the virtual pixel in the original image in accordance with the determined weights and the pixel values of the four actual pixels.

2. The method of image scaling according to claim 1, wherein the step of determining the coordinates of a virtual pixel in an original image uses a scale factor n/m to divide the coordinates of the actual pixel in the scaled target image.

3. The method of image scaling according to claim 1, wherein the step of determining the coordinates of four actual pixels in the original image that are closest to the virtual pixel further includes:

rounding off the coordinates of the virtual pixel in the original image to determine a first actual pixel'"'"'s coordinates (p, q);

determining a second actual pixel'"'"'s coordinates (p+1, q) by increasing the x-coordinate of the first actual pixel by one unit;

determining a third actual pixel'"'"'s coordinates (p, q+1) by increasing the y-coordinate of the first actual pixel by one unit; and

determining a fourth actual pixel'"'"'s coordinates (p+1, q+1) by increasing both the x-coordinate and y-coordinate of the first actual pixel by one unit.

4. The method of image scaling according to claim 3, wherein the step of determining the weights of the four actual pixels further includes:

determining respectively a horizontal residual and a vertical residual of each of the first, second, third, and fourth actual pixels;

determining a horizontal weight in accordance with the horizontal residual of each of the four actual pixels; and

determining a vertical weight in accordance with the vertical residual of each of the four actual pixels.

5. The method of image scaling according to claim 4, wherein the step of determining the pixel value of the virtual pixel in the original image further includes:

determining the pixel value of a first temporary virtual pixel by averaging the pixel values of the first actual pixel and the second actual pixel in accordance with their respective horizontal weights;

determining the pixel value of a second temporary virtual pixel by averaging the pixel values of the third actual pixel and the fourth actual pixel in accordance with their respective horizontal weights; and

determining the pixel value of the virtual pixel by averaging the pixel values of the first temporary virtual pixel and the second temporary virtual pixel in accordance with the four actual pixel'"'"'s respective vertical weights.

6. The method of image scaling according to claim 4, wherein the step of determining the horizontal residual of an actual pixel in the original image further includes:

assigning the horizontal residual a₁ of an actual pixel at the coordinate origin of the original image to be zero;

if the horizontal residual a_N of the N^th actual pixel is greater than or equal to n, setting the horizontal residual a_N+1 of the (N+1)^th actual pixel to be (a_N−

n); and

if the horizontal residual a_N of the N^th actual pixel is less than n, setting the horizontal residual a_N+1 of the (N+1)^th actual pixel is be (a_N+m−

n).

7. The method of image scaling according to claim 6, wherein the step of determining the horizontal weight of an N^th actual pixel in the original image further includes:

if the horizontal residual a_N≧

n, defining the N^th actual pixel to be a minor contributory pixel;

if the horizontal residual a_N<

n, defining the N^th actual pixel to be a major contributory pixel and setting its major horizontal weight to be (n−

a_N); and

if the horizontal residual a_N<

n, defining the (N+1)^th actual pixel to be a minor contributory pixel and setting its minor horizontal weight to be a_N.

8. The method of image scaling according to claim 7, wherein the step of determining the pixel value of the first temporary virtual pixel further includes:

weighting the pixel value of the first actual pixel in accordance with the horizontal weight of the first actual pixel'"'"'s major horizontal contributory pixel;

weighting the pixel value of the second actual pixel in accordance with the horizontal weight of the second actual pixel'"'"'s minor horizontal contributory pixel; and

determining the pixel value of the first temporary virtual pixel in accordance with the weighted pixel values of the first actual pixel and the second actual pixel.

9. The method of image scaling according to claim 4, wherein the step of determining the vertical residual of an actual pixel in the original image further includes:

assigning the vertical residual b₁ of an actual pixel at the coordinate origin of the original image to be zero;

if the vertical residual b_N of the N^th actual pixel is greater than or equal to n, setting the vertical residual b_N+1 of the (N+1)^th actual pixel to be (b_N+1−

n); and

if the vertical residual b_N of the N^th actual pixel is less than n, setting the vertical residual b_N+1 of the (N+1)^th actual pixel to be (b_N+m−

n).

10. The method of image scaling according to claim 9, wherein the step of determining the vertical weight of an N^th actual pixel in the original image further includes:

if the vertical residual b_N≧

n, defining the N^th actual pixel to be a minor contributory pixel;

if the vertical residual b_N<

n, defining the N^th actual pixel to be a major contributory pixel and setting its major vertical weight to be (n−

b_N); and

if the vertical residual b_N<

n, defining the (N+1)^th actual pixel to be a minor contributory pixel and setting its minor horizontal weight to be b_N.

11. The method of image scaling according to claim 10, wherein the step of determining the pixel value of the second temporary virtual pixel further includes:

weighting the pixel value of the third actual pixel in accordance with the horizontal weight of the third actual pixel'"'"'s major horizontal contributory pixel;

weighting the pixel value of the fourth actual pixel in accordance with the horizontal weight of the fourth actual pixel'"'"'s minor horizontal contributory pixel; and

determining the pixel value of the second temporary virtual pixel in accordance with the weighted pixel values of the third actual pixel and the fourth actual pixel.

12. The method of image scaling according to claim 11, wherein the step of determining the pixel value of the virtual pixel in the original image further includes:

weighting the pixel value of the first temporary virtual pixel in accordance with the vertical weight of the first actual pixel'"'"'s major contributory pixel;

weighting the pixel value of the second temporary virtual pixel in accordance with the vertical weight of the third actual pixel'"'"'s minor contributory pixel; and

determining the pixel value of the virtual pixel in accordance with the weighted pixel values of the first temporary virtual pixel and the second temporary virtual pixel.

13. The method of image scaling according to claim 8, wherein the step of determining the pixel value of the virtual pixel in the original image further includes:

weighting the pixel value of the first temporary virtual pixel in accordance with the vertical weight of the first actual pixel'"'"'s major contributory pixel;

weighting the pixel value of the second temporary virtual pixel in accordance with the vertical weight of the third actual pixel'"'"'s minor contributory pixel; and

determining the pixel value of the virtual pixel in accordance with the weighted pixel values of the first temporary virtual pixel and the second temporary virtual pixel.

14. The method of image scaling according to any one of claims 2, wherein the numerator n of the scale factor n/m is a power of 2.