1. Field of the Invention
The present invention relates to an apparatus and method for converting an interlaced image into a progressive image, and more particularly, to an apparatus and method for converting an interlaced image into a progressive image by interpolating the interlaced image considering characteristics of a region and the orientation of an edge to which a pixel to be interpolated belongs.
2. Description of the Related Art
There are various methods of converting an interlaced image into a progressive image. In particular, a blend method and an edge dependent interpolation method are mainly used.
In the blend method, interpolation is performed on an object pixel, using the values of pixels on preceding and following interlaced scan lines corresponding to the object pixel and the values of upper and lower pixels above and below the object pixel, and the result of interpolation is used as the value of the object pixel. The blend method is preferred since an edge of an image can be smoothly and naturally represented. However, when an interlaced image with much motion is converted into a progressive image using the blend method, a blur and an afterimage are likely to occur, and diagonal aliasing may occur at an edge of the image.
In the edge dependent interpolation method, the value of an object pixel, which is to be interpolated, is obtained using the values of pixels above and below the object pixel and the values of pixels to the left and right of the pixels above and below the object pixel.
Referring to FIG. 1, a value obtained by progressively scanning an object pixel X is computed using the value Dlu of a pixel to the upper left of the object pixel, the value Drd of a pixel to the lower right of the object pixel, the value Dru of a pixel to the upper right of the object pixel, and the value Dld of a pixel to the lower left of the object pixel, and the values Vu and Vd of pixels above and below the object pixel.
More specifically, in the edge dependent interpolation method, the value obtained by progressively scanning an object pixel X is obtained by computing the differences between the values Vu and Vd, between the values Dlu and Drd, and between the values Dru and Dld, and then interpolating the object pixel X using pixels disposed in a direction having the smallest value among these differences. This method is advantageous in that slanted edges of an image can be naturally represented since image conversion is made in consideration of pixels disposed diagonally from the object pixel, thus preventing aliasing from occurring in the image.
However, the edge dependent interpolation method is disadvantageous in that the edge orientation in an image is likely to be erroneously determined and use of only one field of an interlaced image during interpolation may cause a large difference between chromaticity values of the interlaced image and a progressive image. Also, color blurring may occur during conversion of an image having an object moving rapidly into a progressive image. Accordingly, the edge dependent interpolation method requires determining whether a pixel is to be interpolated in a diagonal direction or a vertical direction.
Conventionally, the edge orientation in an image is determined by computing absolute values |x(k)−y(−k)| of the differences between values of pixels along an upper scan line and pixels of a lower scan line (k=−N, . . . , 0, . . . , N), and determining that there is a diagonal line in the direction in which the smallest absolute value is obtained. Such a method is disclosed in U.S. Pat. Nos. 5,532,751 and 6,421,090. However, this method requires complex computation to obtain the absolute values of the differences between the values of possible combinations of pixels disposed diagonally from an object pixel. When computing absolute values in only several diagonal directions to reduce computational complexity, defects may occur in an image. Also, motion estimation needed for precise image conversion requires a lot of computation and large memory bandwidth, thus making it difficult to convert an interlaced image into a progressive image in real time.