OpenCV返回黑白图像，而不是灰度图像 [英] OpenCV returns black and white image instead of grayscale

问题描述

以下是我对图像进行预处理的尝试.这涉及以下步骤

The following is my attempt to preprocess an image. That involves the followings steps

1. 戴上口罩
2. 收获结果
3. 最后，将像素值缩放为255

当我尝试从第3步返回到第2步时，我得到的是黑白图像，而不是灰度图像. 以下是我执行预处理的代码

When I try to go back from step 3 to step 2, I get a black and white image instead of a grayscale one. The following is my code to perform preprocessing

cv::Mat maskCrop(std::string imageName, std::string maskName)
{
    cv::Mat image,mask;
    image = cv::imread( imageName, CV_LOAD_IMAGE_GRAYSCALE);
    mask = cv::imread( maskName,CV_LOAD_IMAGE_GRAYSCALE);
    cv::Mat final_image;
    cv::resize(image, image, mask.size());  // make the size of mask and image same

    cv::bitwise_and(image, mask, final_image); //Apply mask

    // define rectangular window for cropping
    int offset_x = 1250;  // top left corner, for cropping
    int offset_y = 1550;

    cv::Rect roi;
    roi.x = offset_x;
    roi.y = offset_y;
    roi.width = 550;
    roi.height = 650;

    // Crop the original image to the defined ROI //

    cv::Mat crop = final_image(roi);
   //scale the image
    float beta = 1.0 / 255.0;
    crop *=beta;  // divide the max pixel vaue i.e. 255

    //Examinig whether scaling can be undone !!!!
    cv::imwrite("/home/dpk/Desktop/ip-rings/gray_image.jpg",crop*255);

    return crop;
}

以下是当我尝试按255撤消缩放比例时获得的输出(第3步)

The following is the output that I get when I try to undo scaling by 255(step 3)

以下是预期的输出

什么导致图像为黑白而不是灰度?

What causes the image to be black and white instead of grayscale?

推荐答案

这是因为数据类...我认为crop矩阵类是uchar，当您除以255时，输出为0或1 (介于0到254之间的每个强度为零，而255为1)，当您在255中乘以输出时，输出将为0和255. 所以测试这段代码

It's because class of data... I assume that the crop matrix class is uchar and when you divide to 255 the output is 0 or 1 (every intensity between 0 to 254 is zero and 255 will be 1) and when you multipy output in 255 the output will be 0 and 255. so test this code

{
.
.
cv::Mat crop = final_image(roi);
crop.convertTo(crop,
               CV_32F,       //New Type
               1.0f/255,     //Scaling
               0);           //offset
cv::imwrite("/home/dpk/Desktop/ip-rings/gray_image.jpg",crop*255);

return crop;
}

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