Interpolation method for enlarging an image

The present invention relates to an interpolation method for enlarging an image, wherein the image is composed of plural scanning lines. Firstly, it selects four adjacent continuous pixels xk−1, xk, xk+1, and xk+2 which have the pixel values f(xk−1), f(xk), f(xk+1), and f(xk+2) respectively on each of the scanning lines; next, it determines three linear equations Lk−1, Lk, and Lk+1 according to every two adjacent pixel values f(xk−1) and f(xk), f(xk) and f(xk+1), and f(xk+1) and f(xk+2), respectively; then, it selects a pixel x to be interpolated between the pixel xk and the pixel xk+1; finally, it applies the pixel x to the three linear equations Lk−1, Lk, and Lk+1 to determine three candidate pixel values which are weighted and combined to obtain pixel value f(x) of the pixel x.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image interpolation method and, more particularly, to an interpolation method for enlarging an image.

2. Description of Related Art

In an image process to enlarge an image, the image of low-pixel has to be enlarged as an image of high-pixel. The image will become indistinct because of loss to the image information. Moreover, this indistinct image reduces the quality of image. In order to avoid this problem, when the image is proceeding to enlarge, a microprocessor uses an interpolation method, such as B-spline or Bicubic, for interpolating pixels to the image to be enlarged, so as to obtain new pixel values to achieve good vision quality. However, the interpolation operation uses a complex cubic polynomial for calculating interpolated pixels. Thus, when proceeding to enlarge for the image, lots of multipliers and adders are required to implement the interpolation operation. Accordingly, such a great amount of operation not only is disadvantageous for hardware implementation but also spends a lot of computation time. Therefore, it is desirable to provide an improved interpolation method for enlarging an image to mitigate and/or obviate the aforementioned problems.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an interpolation method for enlarging an image, which uses a linear interpolation for obtaining interpolated pixel values so as to significantly reduce the amount of computation, thereby being advantageous to hardware implementation and reducing the cost.

To achieve the object, the present invention provides an interpolation method for enlarging an image, wherein the image is composed of plural scanning lines. The method comprises the steps of: (A) selecting four adjacent continuous pixels xk−1, xk, xk+1, and xk+2which have the pixel values f(xk−1), f(xk), f(xk+1), and f(xk+2), respectively, on each of the scanning lines; (B) determining three linear equations Lk−1, Lk, and Lk+1according to every two adjacent pixel values f(xk−1) and f(xk), f(xk) and f(xk+1), and f(xk+1) and f(xk+2), respectively; (C) selecting a pixel x to be interpolated between the pixel xkand the pixel xk+1; (D) applying the pixel x to the three linear equations Lk−1, Lk, and Lk+1to determine three candidate pixel values, respectively, which are weighted and combined to obtain pixel value f(x) of the pixel x.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is an interpolation method for enlarging an image. The steps of the method are shown inFIG. 1. The method of the embodiment will be elaborated inFIG. 2andFIG. 3.

With reference toFIG. 2, there is shown a schematic diagram of an image, wherein the image is composed of plural scanning lines21. Each of the scanning lines21also includes plural pixels x1˜xn. Each of the pixels x1˜xnhas a pixel value. When proceeding to enlarge the image, a microprocessor inserts the interpolated pixels among the pixels x1˜xnof each scanning line21for increasing the number of pixels of the image to achieve effect of enlargement.

Please refer toFIGS. 1 and 3.FIG. 1shows a flowchart of interpolation method for enlarging an image in accordance with the present invention, andFIG. 3shows a schematic diagram of the interpolation method for enlarging an image in accordance with the present invention. Firstly, it selects four adjacent continuous pixels xk−1, xk, xk+1, and xk+2which have the pixel values f(xk−1), f(xk), f(xk+1), and f(xk+2), respectively, on each of the scanning lines21(step A). Next, it determines three linear equations Lk−1, Lk, and Lk+1according to every two adjacent pixel values f(xk−1) and f(xk), f(xk) and f(xk+1), and f(xk+1) and f(xk+2), respectively. Moreover, it computes three slopes, denoted as slope1, slope2, and slope3, for the three linear equations Lk−1, Lk, and Lk+1, respectively (step B).

Then, it selects a pixel x to be interpolated between the pixel xkand the pixel xk+1, wherein the ratio of a distance from the pixel xkto the pixel x to a distance from the pixel (xk) to the pixel (xk+1) is s. The ratio of a distance from the pixel x to the pixel xk+1to a distance from the pixel xkto the pixel xk+1is 1−s (step C). Finally, it applies the pixel x to the three linear equations Lk−1, Lk, and Lk+1to determine three candidate pixel values f1, f2and f3as follows:
f1=slope1×(1−s)+f(xk−1),
f2=slope2×(1−s)+f(xk), and
f3=f(xk+1)−slope3×s.
These three candidate pixel values f1, f2and f3are then weighted by weighting values w1, w2, and w3, respectively, and combined to obtain a pixel value f(x) of the pixel (x) (step D) as follows:
f(x)=w1×[slope1×(1−s)+f(xk−1)]+w2×[slope2×(1−s)+f(xk)]+w3×[f(xk+1)−slope3×s],
where w1=s/2, w2=½, w3=(1−s)/2, w1+w2+w3=1.

Thus, according to the above steps, it is able to proceed to interpolate and compute the pixel values of the interpolation for the pixel values on each of scanning line. When proceeding to enlarge the image, those pixel values of new interpolation avoid producing an indistinct image thereby maintaining the quality of image. The interpolation method of the present invention uses a simple linear equation for obtaining interpolated pixel values so as to significantly reduce the amount of computation, thereby being advantageous to hardware implementation and reducing the cost.