Question

我有一个简单的结构来表示图像的左，上，右，底部用于裁剪的百分比：

struct RoiRect {
    unsigned int left;
    unsigned int top;
    unsigned int right;
    unsigned int bottom;

    bool isAllZero() {
        return left == 0 && top == 0 && left == 0 && bottom == 0;
    }

    void getCvRect(cv::Size cvSize, cv::Rect &cvRect) {
            int height = cvSize.height;
            int width = cvSize.width;

            int x = ((double)(left/height)*100);
            int y = ((double)(top/height)*100);
            int w = width - ((double)(right/width)*100);
            int h = height - ((double)(bottom/width)*100);

            cvRect.x = x;
            cvRect.y = y;
            cvRect.width = w;
            cvRect.height = h;
    }
};

我使用10,15,20,25之类的值初始化此结构。这意味着图像应从右侧裁剪10％，从顶部裁剪15％，依此类推。

在另一个类中，我将调用结构的getCvRect并传入图像大小和原始cv::Rect对象，以便上面的函数计算百分比并返回一个要裁剪的矩形图像：

//inside another function
cv::Rect rect; //rect to be calculated by getCvRect function of the struct
bool crop; //should crop or not? if all == zero then NOT!
if(!mRoiRect.isAllZero()) {
    crop = true;
    mRoiRect.getCvRect(mat.size(), rect);
}

但是所有的努力都是徒劳的！我传入一个大小作为第一个参数，我很确定图像大小是例如640x480 ...函数调用后的rect对象显示640x480 ...所以我的函数绝对没有。

我做错了什么，我该怎样做才能解决或更好地完成这项任务的更聪明方法？

正确的实施方式（对任何有兴趣的人）

    int x = ((double) left / 100) * width;
    int y = ((double) top / 100) * height;
    int w = width - ((double) right / 100) * width;
    int h = height - ((double) bottom / 100) * width;

Answer 1

问题在于四行：

        int x = ((double)(left/height)*100);
        int y = ((double)(top/height)*100);
        int w = width - ((double)(right/width)*100);
        int h = height - ((double)(bottom/width)*100);

这里left/height等...都使用整数除法，然后结果被转换为double。当然，效果是x和y以及零和w == width以及h == height。你打算写的很可能是

        int x = ((double) left)/height*100;
        int y = ((double) top)/height*100;
        int w = width - ((double) right)/width*100;
        int h = height - ((double) bottom)/width*100;

Answer 2

我使用的示例函数可能对改进代码有用

Rect shrinkRect(Rect rect, int width_percent, int height_percent)
{
    if (width_percent > 100) width_percent = 100;
    if (height_percent > 100) height_percent = 100;

    Rect newrect;
    newrect.width = (rect.width * width_percent) / 100;
    newrect.height = (rect.height * height_percent) / 100;
    newrect.x = rect.x + (rect.width - newrect.width) / 2;
    newrect.y = rect.y + (rect.height - newrect.height) / 2;

    return newrect;
}

用法：假设您有Rect r = Rect(0,0,100,100)

你想缩小你的直率％20

Rect shrinkedRect = shrinkRect(r, 80, 80)

shrinkedRect是（10,10,80,80）

您可以为width_percent和height_percent

指定不同的值

struct中的函数不执行任何操作

2 个答案: