行人检测开发中，如何获取EmguCV ConnectedComponentsWithStats的统计数据？

Hey there! Let's break down why you're struggling to get values from the stats matrix when using ConnectedComponentsWithStats() for your pedestrian detection project. I'll walk you through the fix and some key details you might be missing.

First, Understand What stats Contains #

The stats matrix is a 2D array where each row corresponds to a connected component (including the background, usually at index 0). The columns hold these critical values (in order):

• Column 0: X-coordinate of the component's top-left corner
• Column 1: Y-coordinate of the component's top-left corner
• Column 2: Width of the component's bounding box
• Column 3: Height of the component's bounding box
• Column 4: Total area (number of pixels) in the component

Common Issues & Fixes in Your Code #

Looking at your code, you've initialized stats but haven't added logic to read its values. Plus, there's a key prerequisite you might have overlooked:

1. Ensure Your Input is a Binary Image
   ConnectedComponentsWithStats() works best (and as expected) with a binary image (pixels are either 0 or 255). If your greyImage is just a grayscale image (not thresholded), the function will treat every distinct grayscale value as a separate component, leading to messy stats data. Add a threshold step first:

// Convert grayscale to binary (adjust threshold value as needed for your use case)
CvInvoke.Threshold(greyImage, greyImage, 127, 255, ThresholdType.Binary);

2. Read stats Values Correctly
   Use the At<int>() method to access values in the stats matrix. Remember to skip index 0 if you don't need the background component:

var labels = new Mat();
var stats = new Mat();
var centroids = new Mat();

// Add thresholding step first
CvInvoke.Threshold(greyImage, greyImage, 127, 255, ThresholdType.Binary);

var nLabels = CvInvoke.ConnectedComponentsWithStats(greyImage, labels, stats, centroids);
var centroidPoints = new MCvPoint2D64f[nLabels];
centroids.CopyTo(centroidPoints);

// Iterate through each connected component (skip background at index 0)
for (int i = 1; i < nLabels; i++)
{
    // Extract stats values
    int x = stats.At<int>(i, 0);
    int y = stats.At<int>(i, 1);
    int width = stats.At<int>(i, 2);
    int height = stats.At<int>(i, 3);
    int area = stats.At<int>(i, 4);

    // Example: Use these values to draw a bounding box for pedestrian detection
    CvInvoke.Rectangle(greyImage, new Rectangle(x, y, width, height), new Scalar(255, 0, 0), 2);

    // Or process the centroid data you already have
    var centroid = centroidPoints[i];
    CvInvoke.Circle(greyImage, new Point((int)centroid.X, (int)centroid.Y), 3, new Scalar(0, 255, 0), -1);
}

Key Notes #

• The stats matrix uses the CV_32S data type (32-bit integers), so we use At<int>() to read values.
• Index 0 in nLabels is almost always the background component—unless you've configured the function otherwise—so skipping it keeps your focus on actual foreground objects (like pedestrians).
• Adjust the threshold value (127 in the example) based on your input images to get clean binary segmentation, which directly impacts the quality of your connected components and stats data.

内容的提问来源于stack exchange，提问作者evadin