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 CS8602
namespace 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);
}
}
}
3 运行效果
3x3的卷积核显然太小了，效果不明显。
