如何创建半透明形状？

Question

如何创建半透明形状？

37

我想知道如何在OpenCV中绘制半透明的形状，类似于下面图片中的形状（来自http://tellthattomycamera.wordpress.com/）：

enter image description here

我不需要那些奇特的圆形，但我想要能够在一个三通道彩色图像上绘制一个矩形，并指定矩形的透明度，就像这样：

rectangle (img, Point (100,100), Point (300,300), Scalar (0,125,125,0.4), CV_FILLED);

其中0,125,125是矩形的颜色，0.4指定透明度。然而，OpenCV的绘图功能中没有这种功能。我该如何在OpenCV中绘制形状，以便可以看到部分原始图像?

- Bokonon

4个回答

20

在OpenCV 3中，这段代码对我起作用：

cv::Mat source = cv::imread("IMG_2083s.png");
cv::Mat overlay;
double alpha = 0.3;

// copy the source image to an overlay
source.copyTo(overlay);

// draw a filled, yellow rectangle on the overlay copy
cv::rectangle(overlay, cv::Rect(100, 100, 300, 300), cv::Scalar(0, 125, 125), -1);

// blend the overlay with the source image
cv::addWeighted(overlay, alpha, source, 1 - alpha, 0, source);

参考/灵感来源：http://bistr-o-mathik.org/2012/06/13/simple-transparency-in-opencv/

- Alexander Taubenkorb

3

除了Alexander Taubenkorb的回答之外，您还可以通过替换cv::rectangle行中的形状来绘制随机（半透明）形状。

例如，如果您想要绘制一系列半透明圆形，则可以按照以下方式进行：

cv::Mat source = cv::imread("IMG_2083s.png");  // loading the source image
cv::Mat overlay;  // declaring overlay matrix, we'll copy source image to this matrix
double alpha = 0.3;  // defining opacity value, 0 means fully transparent, 1 means fully opaque

source.copyTo(overlay);  // copying the source image to overlay matrix, we'll be drawing shapes on overlay matrix and we'll blend it with original image

// change this section to draw the shapes you want to draw
vector<Point>::const_iterator points_it;  // declaring points iterator
for( points_it = circles.begin(); points_it != circles.end(); ++points_it )  // circles is a vector of points, containing center of each circle
    circle(overlay, *points_it, 1, (0, 255, 255), -1);  // drawing circles on overlay image


cv::addWeighted(overlay, alpha, source, 1 - alpha, 0, source);  // blending the overlay (with alpha opacity) with the source image (with 1-alpha opacity)

- Safwan

1

对于C ++，我个人喜欢使用重载运算符来进行标量乘法和矩阵加法的可读性：

... same initial lines as other answers above ...

// blend the overlay with the source image
source = source * (1.0 - alpha) + overlay * alpha;

- MaRib

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- Bull · Accepted Answer

下面的图片使用OpenCV演示了透明度。您需要在图像和矩形之间进行alpha混合。以下是一种实现方法的代码。

enter image description here

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>

int main( int argc, char** argv )
{
    cv::Mat image = cv::imread("IMG_2083s.png"); 
    cv::Mat roi = image(cv::Rect(100, 100, 300, 300));
    cv::Mat color(roi.size(), CV_8UC3, cv::Scalar(0, 125, 125)); 
    double alpha = 0.3;
    cv::addWeighted(color, alpha, roi, 1.0 - alpha , 0.0, roi); 

    cv::imshow("image",image);
    cv::waitKey(0);
}