C++ 如何创建半透明形状？
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How to create a semi transparent shape?
提问by user3788572
I would like to know how to draw semi-transparent shapes in OpenCV, similar to those in the image below (from http://tellthattomycamera.wordpress.com/)
我想知道如何在 OpenCV 中绘制半透明形状，类似于下图（来自http://tellthattomycamera.wordpress.com/）
I don't need those fancy circles, but I would like to be able to draw a rectangle, e.g, on a 3 channel color image and specify the transparency of the rectangle, something like
我不需要那些花哨的圆圈，但我希望能够绘制一个矩形，例如，在 3 通道彩色图像上并指定矩形的透明度，例如
rectangle (img, Point (100,100), Point (300,300), Scalar (0,125,125,0.4), CV_FILLED);
where 0,125,125is the color of the rectangle and 0.4specifies the transparency.
However OpenCV doesn't have this functionality built into its drawing functions. How can I draw shapes in OpenCV so that the original image being drawn on is partially visible through the shape?
其中0,125,125是矩形的颜色并0.4指定透明度。但是，OpenCV 的绘图功能中没有内置此功能。如何在 OpenCV 中绘制形状，以便通过形状部分可见正在绘制的原始图像？
回答by Bull
The image below illustrates transparency using OpenCV. You need to do an alpha blend between the image and the rectangle. Below is the code for one way to do this.
下图说明了使用 OpenCV 的透明度。您需要在图像和矩形之间进行 alpha 混合。下面是执行此操作的一种方法的代码。
#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);
}
回答by Alexander Taubenkorb
In OpenCV 3 this code worked for me:
在 OpenCV 3 中，这段代码对我有用：
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);
Source/Inspired by: http://bistr-o-mathik.org/2012/06/13/simple-transparency-in-opencv/
来源/灵感来源：http: //bistr-o-mathik.org/2012/06/13/simple-transparency-in-opencv/
回答by Safwan
Adding to Alexander Taubenkorb's answer, you can draw random (semi-transparent) shapes by replacing the cv::rectangleline with the shape you want to draw.
添加到 Alexander Taubenkorb 的答案中，您可以通过用cv::rectangle要绘制的形状替换线条来绘制随机（半透明）形状。
For example, if you want to draw a series of semi-transparent circles, you can do it as follows:
例如，如果你想画一系列半透明的圆，你可以这样做：
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)
回答by MaRib
For C++, I personally like the readability of overloaded operators for scalar multiplication and matrix addition:
对于 C++，我个人喜欢用于标量乘法和矩阵加法的重载运算符的可读性：
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
source = source * (1.0 - alpha) + overlay * alpha;
