java Android 上的 OpenCV 转换为灰度不起作用
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OpenCV on Android converting to grayscale not working
提问by Pax0r
I am trying to convert some OpenCV Mat to grayscale for Contours detection algorithms. For some reason the image after convertion is all black. Mine code (b is Android Bitmap):
我正在尝试将一些 OpenCV Mat 转换为轮廓检测算法的灰度。由于某种原因，转换后的图像全黑。我的代码（b是Android Bitmap）：
Mat tmp = new Mat (b.getWidth(), b.getHeight(), CvType.CV_8UC1);
Utils.bitmapToMat(b, tmp);
Imgproc.cvtColor(tmp, tmp, Imgproc.COLOR_BGR2GRAY);
//there could be some processing
Imgproc.cvtColor(tmp, tmp, Imgproc.COLOR_GRAY2BGRA, 4);
Utils.matToBitmap(tmp, b);
And now I am drawing this bitmap and it is all black. When I applied contour detection to this bitmap (in place of comment) there were no match, so I assume problem is with convertion. After removing convertion (simply call bitmapToMat and matToBitmap) then bitmap is not all black so convertion to Mat are also working. Bitmap is in ARGB_8888 and there are no errors, just the output bitmap is all black.
现在我正在绘制这个位图，它是全黑的。当我对此位图（代替注释）应用轮廓检测时，没有匹配，所以我认为问题出在转换上。删除转换后（简单地调用 bitmapToMat 和 matToBitmap）然后位图不是全黑的，所以转换为 Mat 也有效。位图在ARGB_8888中，没有错误，只是输出位图全黑。
Edit: Just to be sure I tried to save a bitmap with ocv imwrite - it's still all black so the problem is for 100% at cvtColor...
编辑：为了确保我尝试用 ocv imwrite 保存位图 - 它仍然是全黑的，所以问题是 cvtColor 100％......
回答by Karthik Balakrishnan
If the bitmap b is from the android device, then try using COLOR_RGB2GRAYinstead of COLOR_BGR2GRAYbecause BGRis the default pixel format for OpenCV images, not all images.
如果位图 b 来自 android 设备，则尝试使用COLOR_RGB2GRAY而不是COLOR_BGR2GRAY因为BGR是 OpenCV 图像的默认像素格式，而不是所有图像。
Try this code:
试试这个代码：
Mat tmp = new Mat (b.getWidth(), b.getHeight(), CvType.CV_8UC1);
Utils.bitmapToMat(b, tmp);
Imgproc.cvtColor(tmp, tmp, Imgproc.COLOR_RGB2GRAY);
//there could be some processing
Imgproc.cvtColor(tmp, tmp, Imgproc.COLOR_GRAY2RGB, 4);
Utils.matToBitmap(tmp, b);
回答by Gaby Bou Tayeh
I tried this method and it works perfectly, first you must convert it into grey scale, then to Canny, and finally to Bitmap.
我试过这个方法，效果很好，首先你必须把它转换成灰度，然后是Canny，最后是位图。
this function returns a black and white image.
此函数返回黑白图像。
public static Bitmap edgesim(Mat img1) {
Bitmap image1;
//mat gray img1 holder
Mat imageGray1 = new Mat();
//mat canny image
Mat imageCny1 = new Mat();
//mat canny image
Mat imageCny2 = new Mat();
/////////////////////////////////////////////////////////////////
//Convert img1 into gray image
Imgproc.cvtColor(img1, imageGray1, Imgproc.COLOR_BGR2GRAY);
//Canny Edge Detection
Imgproc.Canny(imageGray1, imageCny1, 10, 100, 3, true);
///////////////////////////////////////////////////////////////////
//////////////////Transform Canny to Bitmap/////////////////////////////////////////
image1= Bitmap.createBitmap(imageCny1.cols(), imageCny1.rows(), Bitmap.Config.ARGB_8888);
Utils.matToBitmap(imageCny1, image1);
return image1;
}
}
