C#图像处理OpenCV开发指南（CVStar，07）——通用滤波（Filter2D）的实例代码

1 函数定义

void Filter2D   (Mat src,
Mat dst,
int    ddepth,
InputArray    kernel,
Point    anchor = Point(-1,-1),
double    delta = 0,
int    borderType = BORDER_DEFAULT
)

1.1 原型

#include <opencv2/imgproc.hpp>

Convolves an image with the kernel.

使用内核对图像进行卷积。

The function applies an arbitrary linear filter to an image. In-place operation is supported. When the aperture is partially outside the image, the function interpolates outlier pixel values according to the specified border mode.

该函数将任意线性滤波器应用于图像。支持就地操作。当光圈部分位于图像之外时，该函数会根据指定的边界模式对异常像素值进行插值。

The function does actually compute correlation, not the convolution:

That is, the kernel is not mirrored around the anchor point. If you need a real convolution, flip the kernel using flip and set the new anchor to (kernel.cols - anchor.x - 1, kernel.rows - anchor.y - 1).

The function uses the DFT-based algorithm in case of sufficiently large kernels (~11 x 11 or larger) and the direct algorithm for small kernels.

1.2 参数说明 Parameters

src input image. 输入图像。
dst output image of the same size and the same number of channels as src. 输出与src具有相同大小和相同通道数的图像。
ddepth desired depth of the destination image, see combinations 目标图像的所需深度，请参阅组合
kernel convolution kernel (or rather a correlation kernel), a single-channel floating point matrix; if you want to apply different kernels to different channels, split the image into separate color planes using split and process them individually. 核卷积核（或者更确切地说是相关核）、单通道浮点矩阵；如果要将不同的内核应用于不同的通道，请使用split将图像拆分为单独的颜色平面，然后分别进行处理。
anchor anchor of the kernel that indicates the relative position of a filtered point within the kernel; the anchor should lie within the kernel; default value (-1,-1) means that the anchor is at the kernel center. 所述内核的锚定锚，所述锚定锚指示所述内核内的滤波点的相对位置；锚应该位于内核内；默认值（-1，-1）表示锚点位于内核中心。
delta optional value added to the filtered pixels before storing them in dst. 可选值，在将滤波像素存储在dst中之前添加到滤波像素。
borderType pixel extrapolation method, see BorderTypes. BORDER_WRAP is not supported. 像素外推法，请参见BorderTypes。不支持BORDER_WRAP。

2 代码解释

2.1 核心代码


private void Filter2D(object? sender, EventArgs? e)
{Mat src = Cv2.ImRead(sourceImage);Mat dst = new Mat();// 自定义卷积核（通用过滤）InputArray arr = InputArray.Create<float>(new float[3, 3] {{ 0, -1, 0 },{ -1, 5, -1 },{ 0, -1, 0 }});Cv2.Filter2D(src: src,dst: dst,ddepth: -1,kernel: arr,anchor: new OpenCvSharp.Point(-1, -1),delta: 0,borderType: BorderTypes.Default);picResult.Image = CVUtility.Mat2Bitmap(dst);PicAutosize(picResult);
}

通过修改 arr 卷积核矩阵，可获得不同的效果。

2.2 Form1.cs 完整源程序

using OpenCvSharp;#pragma warning disable CS8602namespace Legal.Truffer.CVStar
{public partial class Form1 : Form{string[] ImgExtentions = {"*.*|*.*","JPEG|*.jpg;*.jpeg","GIF|*.gif","PNG|*.png","TIF|*.tif;*.tiff","BMP|*.bmp"};private int original_width { get; set; } = 0;private int original_height { get; set; } = 0;private string sourceImage { get; set; } = "";Panel? panelTop { get; set; } = null;Panel? panelBotton { get; set; } = null;PictureBox? picSource { get; set; } = null;PictureBox? picResult { get; set; } = null;Button? btnLoad { get; set; } = null;Button? btnSave { get; set; } = null;Button? btnFunction { get; set; } = null;public Form1(){InitializeComponent();this.Text = "OPENCV C#编程入手教程 POWERED BY 深度混淆（CSDN.NET）";this.StartPosition = FormStartPosition.CenterScreen;GUI();this.Resize += FormResize;}private void FormResize(object? sender, EventArgs? e){if (this.Width < 200) { this.Width = 320; return; }if (this.Height < 200) { this.Height = 320; return; }GUI();}private void GUI(){if (panelTop == null) panelTop = new Panel();panelTop.Parent = this;panelTop.Top = 5;panelTop.Left = 5;panelTop.Width = this.Width - 26;panelTop.Height = 85;panelTop.BorderStyle = BorderStyle.FixedSingle;panelTop.BackColor = Color.FromArgb(200, 200, 255);if (panelBotton == null) panelBotton = new Panel();panelBotton.Parent = this;panelBotton.Top = panelTop.Top + panelTop.Height + 3;panelBotton.Left = 5;panelBotton.Width = panelTop.Width;panelBotton.Height = this.Height - panelBotton.Top - 55;panelBotton.BorderStyle = BorderStyle.FixedSingle;if (picSource == null) picSource = new PictureBox();picSource.Parent = panelBotton;picSource.Left = 5;picSource.Top = 5;picSource.Width = (panelBotton.Width - 10) / 2;picSource.Height = (panelBotton.Height - 10);picSource.BorderStyle = BorderStyle.FixedSingle;if (picResult == null) picResult = new PictureBox();picResult.Parent = panelBotton;picResult.Left = picSource.Left + picSource.Width + 5;picResult.Top = picSource.Top;picResult.Width = picSource.Width;picResult.Height = picSource.Height;picResult.BorderStyle = BorderStyle.FixedSingle;original_width = picSource.Width;original_height = picSource.Height;if (btnLoad == null) btnLoad = new Button();btnLoad.Parent = panelTop;btnLoad.Left = 5;btnLoad.Top = 5;btnLoad.Width = 90;btnLoad.Height = 38;btnLoad.Cursor = Cursors.Hand;btnLoad.Text = "Load";btnLoad.Click += Load_Image;btnLoad.BackColor = Color.LightCoral;if (btnSave == null) btnSave = new Button();btnSave.Parent = panelTop;btnSave.Left = panelTop.Width - btnSave.Width - 25;btnSave.Top = btnLoad.Top;btnSave.Width = 90;btnSave.Height = 38;btnSave.Cursor = Cursors.Hand;btnSave.Text = "Save";btnSave.Click += Save;btnSave.BackColor = Color.LightCoral;if (btnFunction == null) btnFunction = new Button();btnFunction.Parent = panelTop;btnFunction.Left = btnLoad.Left + btnLoad.Width + 5;btnFunction.Top = btnLoad.Top;btnFunction.Width = 90;btnFunction.Height = 38;btnFunction.Cursor = Cursors.Hand;btnFunction.Text = "Filter2D";btnFunction.Click += Filter2D;btnFunction.BackColor = Color.LightCoral;PicAutosize(picSource);PicAutosize(picResult);}private void Load_Image(object? sender, EventArgs? e){OpenFileDialog openFileDialog = new OpenFileDialog();openFileDialog.Filter = String.Join("|", ImgExtentions);if (openFileDialog.ShowDialog() == DialogResult.OK){sourceImage = openFileDialog.FileName;picSource.Image = Image.FromFile(sourceImage);picResult.Image = picSource.Image;PicAutosize(picSource);PicAutosize(picResult);}}private void PicAutosize(PictureBox pb){if (pb == null) return;if (pb.Image == null) return;Image img = pb.Image;int w = original_width;int h = w * img.Height / img.Width;if (h > original_height){h = original_height;w = h * img.Width / img.Height;}pb.SizeMode = PictureBoxSizeMode.Zoom;pb.Width = w;pb.Height = h;pb.Image = img;pb.Refresh();}private void Save(object? sender, EventArgs? e){SaveFileDialog saveFileDialog = new SaveFileDialog();saveFileDialog.Filter = String.Join("|", ImgExtentions);if (saveFileDialog.ShowDialog() == DialogResult.OK){picResult.Image.Save(saveFileDialog.FileName);MessageBox.Show("Image Save to " + saveFileDialog.FileName);}}private void Filter2D(object? sender, EventArgs? e){Mat src = Cv2.ImRead(sourceImage);Mat dst = new Mat();// 自定义卷积核（通用过滤）InputArray arr = InputArray.Create<float>(new float[3, 3] {{ 0, -1, 0 },{ -1, 5, -1 },{ 0, -1, 0 }});Cv2.Filter2D(src: src,dst: dst,ddepth: -1,kernel: arr,anchor: new OpenCvSharp.Point(-1, -1),delta: 0,borderType: BorderTypes.Default);picResult.Image = CVUtility.Mat2Bitmap(dst);PicAutosize(picResult);}}
}