Interpolation method for enlarging an image

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.

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 x k−1 , x k , x k+1 , and x k+2 which have the pixel values f(x k−1 ), f(x k ), f(x k+1 ), and f(x k+2 ), respectively, on each of the scanning lines; (B) determining three linear equations L k−1 , L k , and L k+1 according to every two adjacent pixel values f(x k−1 ) and f(x k ), f(x k ) and f(x k+1 ), and f(x k+1 ) and f(x k+2 ), respectively; (C) selecting a pixel x to be interpolated between the pixel x k and the pixel x k+1 ; (D) applying the pixel x to the three linear equations L k−1 , L k , and L k+1 to determine three candidate pixel values, respectively, which are weighted and combined to obtain pixel value f(x) of the pixel x.

Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

FIG. 1 is a flowchart of interpolation for enlarging an image in accordance with the present invention;

FIG. 2 is a schematic view of an image; and

FIG. 3 is a schematic diagram of interpolation for enlarging an image in accordance with the present invention.

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

With reference to FIG. 2 , there is shown a schematic diagram of an image, wherein the image is composed of plural scanning lines 21 . Each of the scanning lines 21 also includes plural pixels x 1 ˜x n . Each of the pixels x 1 ˜x n has a pixel value. When proceeding to enlarge the image, a microprocessor inserts the interpolated pixels among the pixels x 1 ˜x n of each scanning line 21 for increasing the number of pixels of the image to achieve effect of enlargement.

Please refer to FIGS. 1 and 3 . FIG. 1 shows a flowchart of interpolation method for enlarging an image in accordance with the present invention, and FIG. 3 shows a schematic diagram of the interpolation method for enlarging an image in accordance with the present invention. Firstly, it selects four adjacent continuous pixels x k−1 , x k , x k+1 , and x k+2 which have the pixel values f(x k−1 ), f(x k ), f(x k+1 ), and f(x k+2 ), respectively, on each of the scanning lines 21 (step A). Next, it determines three linear equations L k−1 , L k , and L k+1 according to every two adjacent pixel values f(x k−1 ) and f(x k ), f(x k ) and f(x k+1 ), and f(x k+1 ) and f(x k+2 ), respectively. Moreover, it computes three slopes, denoted as slope 1 , slope 2 , and slope 3 , for the three linear equations L k−1 , L k , and L k+1 , respectively (step B).

Then, it selects a pixel x to be interpolated between the pixel x k and the pixel x k+1 , wherein the ratio of a distance from the pixel x k to the pixel x to a distance from the pixel (x k ) to the pixel (x k+1 ) is s. The ratio of a distance from the pixel x to the pixel x k+1 to a distance from the pixel x k to the pixel x k+1 is 1−s (step C). Finally, it applies the pixel x to the three linear equations L k−1 , L k , and L k+1 to determine three candidate pixel values f 1 , f 2 and f 3 as follows:

f 1=slope1×(1 −s )+ f ( x k−1 ),

f 2=slope2×(1− s )+ f ( x k ), and

f 3= f ( x k+1 )−slope3× s.

These three candidate pixel values f 1 , f 2 and f 3 are then weighted by weighting values w 1 , w 2 , and w 3 , respectively, and combined to obtain a pixel value f(x) of the pixel (x) (step D) as follows:

f ( x )= w 1×[slope1×(1− s )+ f ( x k−1 )]+ w 2×[slope2×(1 −s )+ f ( x k )]+ w 3 ×[f ( x k+1 )−slope3× s],

where w 1 =s/2, w 2 =½, w 3 =(1−s)/2, w 1 +w 2 +w 3 =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.

Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.