OpenCV显示错误的颜色

Question

我正在使用C ++使用OpenCV。我想用三种颜色创建图像：红色，白色和黑色。详细地说，根据某些条件，我希望背景为红色，然后为白色，部分为黑色。

我的问题是，当我将颜色设置为白色时，它变成蓝色。

有人可以知道为什么会这样以及如何解决吗？

这是我的代码：

    //initial image total red

    cv::Mat image(Size(w, h), CV_8UC3, cv::Scalar(0, 0, 255));          

    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            int pixel_v = (int)imggray.at<uchar>(i,j);
            if (pixel_v < 200) {                
                int pixel_bl = (int)imgBool.at<uchar>(i, j);
                if (pixel_bl > 200) {
                    //HERE A WANT WHITE PIXELS, but they are blue
                    image.at<Vec3b>(i, j) = (255, 255, 255);                        
                }
                else {
                    //black: this works
                    image.at<Vec3b>(i, j) = (0, 0, 0);

                }
            }


        }
    }

Answer 1

OpenCV使用图像格式BGR（蓝色，绿色，红色）

写此行时：

 image.at<Vec3b>(i, j) = (255, 255, 255);             

等价于：

image.at<Vec3b>(i, j) = (255);             

（（请参阅this SO answer解释原因。]

[仅将第一个通道设置为max，而恰好是蓝色。

您需要做的是编辑整个像素，如下所示：

    // get pixel
    Vec3b color = image.at<Vec3b>(Point(x,y));

    color[0] = 255;
    color[1] = 255;
    color[2] = 255;

    // set pixel
    image.at<Vec3b>(Point(x,y)) = color;

Borrowed from this answer

所以您的代码需要看起来像这样：

cv::Mat image(Size(w, h), CV_8UC3, cv::Scalar(0, 0, 255));          

for (int i = 0; i < h; i++) {
    for (int j = 0; j < w; j++) {
        int pixel_v = (int)imggray.at<uchar>(i,j);
        if (pixel_v < 200) {                
            int pixel_bl = (int)imgBool.at<uchar>(i, j);
            if (pixel_bl > 200) {
                //HERE A WANT WHITE PIXELS, but they are blue
                Vec3b color = image.at<Vec3b>(Point(i,j));
                color[0] = 255;
                color[1] = 255;
                color[2] = 255;
                image.at<Vec3b>(Point(i,j)) = color;                   
            }
            else {
                image.at<Vec3b>(i, j) = (0, 0, 0);

            }
        }
    }
}

Answer 2

我在C ++中使用opencv。我从Java接收图像，然后使用此方法将其放入缓冲区：

private fun YUV_420_888_dataToBuffer(image: Image): ByteArray? {
     try {
   val imageWidth = image.width
   val imageHeight = image.height
   val planes = image.planes
   val data = ByteArray(imageWidth * imageHeight *  ImageFormat.getBitsPerPixel(ImageFormat.YUV_420_888) / 8 )
   var offset = 0
   for (plane in planes.indices) {
       val buffer = planes[plane].buffer
       val rowStride = planes[plane].rowStride

       val pixelStride = planes[plane].pixelStride
       val planeWidth = if (plane == 0) imageWidth else imageWidth / 2
       val planeHeight = if (plane == 0) imageHeight else imageHeight / 2
       if (pixelStride == 1 && rowStride == planeWidth) {
           // Copy whole plane from buffer into |data| at once.
           buffer[data, offset, planeWidth * planeHeight]
           offset += planeWidth * planeHeight
       } else {
           // Copy pixels one by one respecting pixelStride and rowStride.
           val rowData = ByteArray(rowStride)
           for (row in 0 until planeHeight - 1) {
               buffer[rowData, 0, rowStride]
               for (col in 0 until planeWidth) {
                   data[offset++] = rowData[col * pixelStride]
               }
           } 
           buffer[rowData, 0, Math.min(rowStride, buffer.remaining())]
           for (col in 0 until planeWidth) {
               data[offset++] = rowData[col * pixelStride]
           }
       }
   }
   return data
  } catch (e: Exception) {
   return null
 }
    }

在c ++方面，我正在像这样从字节数组创建Mat：

 Mat * myuv = new Mat(width, height, CV_8UC1, (unsigned char *)  data);

 cvtColor(*myuv, *myuv, COLOR_YUV420sp2RGBA, 4);

这里出了什么问题？