c ++和opencv获取并将像素颜色设置为Mat
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c++ and opencv get and set pixel color to Mat
提问by grll
I'm trying to set a new color value to some pixel into a cv::Mat image my code is below:
我正在尝试将某个像素的新颜色值设置为 cv::Mat 图像，我的代码如下：
Mat image = img;
for(int y=0;y<img.rows;y++)
{
for(int x=0;x<img.cols;x++)
{
Vec3b color = image.at<Vec3b>(Point(x,y));
if(color[0] > 150 && color[1] > 150 && color[2] > 150)
{
color[0] = 0;
color[1] = 0;
color[2] = 0;
cout << "Pixel >200 :" << x << "," << y << endl;
}
else
{
color.val[0] = 255;
color.val[1] = 255;
color.val[2] = 255;
}
}
imwrite("../images/imgopti"+to_string(i)+".tiff",image);
It seems to get the good pixel in output (with cout) however in the output image (with imwrite) the pixel concerned aren't modified. I have already tried using color.val[0].. I still can't figure out why the pixel colors in the output image dont change. thanks
它似乎在输出（使用 cout）中获得了良好的像素，但是在输出图像（使用 imwrite）中，相关像素没有被修改。我已经尝试过使用 color.val[0] .. 我仍然无法弄清楚为什么输出图像中的像素颜色没有改变。谢谢
回答by Roger Rowland
You did everything except copying the new pixel value back to the image.
除了将新像素值复制回图像之外，您已完成所有操作。
This line takes a copy of the pixel into a local variable:
此行将像素的副本复制到局部变量中：
Vec3b color = image.at<Vec3b>(Point(x,y));
So, after changing coloras you require, just set it back like this:
因此，color根据需要进行更改后，只需将其设置回如下：
image.at<Vec3b>(Point(x,y)) = color;
So, in full, something like this:
所以，完整的，是这样的：
Mat image = img;
for(int y=0;y<img.rows;y++)
{
for(int x=0;x<img.cols;x++)
{
// get pixel
Vec3b & color = image.at<Vec3b>(y,x);
// ... do something to the color ....
color[0] = 13;
color[1] = 13;
color[2] = 13;
// set pixel
//image.at<Vec3b>(Point(x,y)) = color;
//if you copy value
}
}
回答by berak
just use a reference:
只需使用参考：
Vec3b & color = image.at<Vec3b>(y,x);
color[2] = 13;
回答by Flocke
I would not use .at for performance reasons.
出于性能原因，我不会使用 .at。
Define a struct:
定义一个结构：
//#pragma pack(push, 2) //not useful (see comments below)
struct RGB {
uchar blue;
uchar green;
uchar red; };
And then use it like this on your cv::Mat image:
然后在你的 cv::Mat 图像上像这样使用它：
RGB& rgb = image.ptr<RGB>(y)[x];
image.ptr(y) gives you a pointer to the scanline y. And iterate through the pixels with loops of x and y
image.ptr(y) 给你一个指向扫描线 y 的指针。并使用 x 和 y 循环遍历像素
