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我正在尝试缩小我捕获的 X 显示器的大小，以便在新窗口中显示它。我尝试平均单个 RGB 分量，但图像看起来不太好。这是我的算法：

  img = XGetImage(d_remote,RootWindow(d_remote,0),0,0,attr.width,attr.height,XAllPlanes(),ZPixmap);

   int i;
   int j;
   for(i=0;i<attr.height;i=i+2){
        for(j=0;j<attr.width;j=j+2) {
                unsigned long p1 = XGetPixel(img, j, i);
                unsigned long p1R = p1 & 0x00ff0000;
                unsigned long p1G = p1 & 0x0000ff00;
                unsigned long p1B = p1 & 0x000000ff;

                unsigned long p2 = XGetPixel(img, j+1, i);
                unsigned long p2R = p2 & 0x00ff0000;
                unsigned long p2G = p2 & 0x0000ff00;
                unsigned long p2B = p2 & 0x000000ff;

                unsigned long p3 = XGetPixel(img, j, i+1);
                unsigned long p3R = p3 & 0x00ff0000;
                unsigned long p3G = p3 & 0x0000ff00;
                unsigned long p3B = p3 & 0x000000ff;

                unsigned long p4 = XGetPixel(img, j+1, i+1);
                unsigned long p4R = p4 & 0x00ff0000;
                unsigned long p4G = p4 & 0x0000ff00;
                unsigned long p4B = p4 & 0x000000ff;

                unsigned long averageR = (p1R+p2R+p3R+p4R)/4;
                unsigned long averageG = (p1G+p2G+p3G+p4G)/4;
                unsigned long averageB = (p1B+p2B+p3B+p4B)/4;

                int average = averageR | averageG | averageB | 0x00000000;

                XPutPixel(newImg, j/2, i/2, average);

        }
   }

平均像素是一种不好的方法吗？我基本上是在尝试将 img 缩放 50%。我的假设是我在像素图上移动一个 2x2 正方形。

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1 回答 1

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在这样做：

unsigned long averageR = (p1R+p2R+p3R+p4R)/4;
unsigned long averageG = (p1G+p2G+p3G+p4G)/4;
unsigned long averageB = (p1B+p2B+p3B+p4B)/4;

int average = averageR | averageG | averageB | 0x00000000;

您正在“污染”您的颜色：如果 (p1R+p2R+p3R+p4R) 的总和不能被 4 整除，那么您将有位进入 G 字段（在最高有效位中！）。(p1G+p2G+p3G+p4G) 和 B 字段相同。你应该做：

unsigned long averageR = (p1R+p2R+p3R+p4R)/4  & 0x00ff0000;
unsigned long averageG = (p1G+p2G+p3G+p4G)/4  & 0x0000ff00;
unsigned long averageB = (p1B+p2B+p3B+p4B)/4  & 0x000000ff;

int average = averageR | averageG | averageB;

最后一个 `0x00000000 不是必需的，它绝对什么都不做:)

（我还仔细检查了运算符优先级，应该没问题）

于 2013-07-11T21:27:29.737 回答