我收到了一段使用双线性插值缩放图像的代码。我知道这段代码是可行的,但有一件事情我想不明白:如果所估计的像素值是输入图像中的边缘像素(即在最后一行或最后一列),那么我怎么能得到坐标为(x+1,y+1)的像素,这应该会导致数组索引超出范围错误,但实际上并没有发生这样的错误,为什么呢? 以下是代码:
public int[] resizeBilinearGray(int[] pixels, int w, int h, int w2, int h2) {
int[] temp = new int[w2*h2] ;
int A, B, C, D, x, y, index, gray ;
float x_ratio = ((float)(w-1))/w2 ;
float y_ratio = ((float)(h-1))/h2 ;
float x_diff, y_diff, ya, yb ;
int offset = 0 ;
for (int i=0;i<h2;i++) {
for (int j=0;j<w2;j++) {
x = (int)(x_ratio * j) ;
y = (int)(y_ratio * i) ;
x_diff = (x_ratio * j) - x ;
y_diff = (y_ratio * i) - y ;
index = y*w+x ;
// range is 0 to 255 thus bitwise AND with 0xff
A = pixels[index] & 0xff ;
B = pixels[index+1] & 0xff ;
C = pixels[index+w] & 0xff ;
D = pixels[index+w+1] & 0xff ;
// Y = A(1-w)(1-h) + B(w)(1-h) + C(h)(1-w) + Dwh
gray = (int)(
A*(1-x_diff)*(1-y_diff) + B*(x_diff)*(1-y_diff) +
C*(y_diff)*(1-x_diff) + D*(x_diff*y_diff)
) ;
temp[offset++] = gray ;
}
}
return temp ;
}