在 C# 中使用多线程屏蔽/过滤图像（Windows 窗体应用程序）
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【中文标题】在 C# 中使用多线程屏蔽/过滤图像（Windows 窗体应用程序）【英文标题】：Using Multithreading to mask/filter a image in C# (windows form application) 【发布时间】：2018-10-16 06:19:36 【问题描述】：我目前正在尝试学习如何在 C# 中使用多线程，但我真的很难让用户从 UI 中选择要使用的线程数。
在一些来源的帮助下，我编写了代码以使用中值滤波器屏蔽图像，现在想应用多线程 (1-64)。
我知道线程是如何工作的，但我正在努力寻找在这个程序中实现它的方法。
有人可以帮助我理解吗，不要向我展示所需的代码，而是解释应该在哪里实现线程以及如何允许用户选择线程数量。
代码
类 ExtBitmap
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Drawing.Imaging;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Drawing.Drawing2D;
namespace EilandFotoPRAK1
public static class ExtBitmap
public static Bitmap CopyToSquareCanvas(this Bitmap sourceBitmap, int canvasWidthLenght)
float ratio = 1.0f;
int maxSide = sourceBitmap.Width > sourceBitmap.Height ?
sourceBitmap.Width : sourceBitmap.Height;
ratio = (float)maxSide / (float)canvasWidthLenght;
Bitmap bitmapResult = (sourceBitmap.Width > sourceBitmap.Height ?
new Bitmap(canvasWidthLenght, (int)(sourceBitmap.Height / ratio))
: new Bitmap((int)(sourceBitmap.Width / ratio), canvasWidthLenght));
using (Graphics graphicsResult = Graphics.FromImage(bitmapResult))
graphicsResult.CompositingQuality = CompositingQuality.HighQuality;
graphicsResult.InterpolationMode = InterpolationMode.HighQualityBicubic;
graphicsResult.PixelOffsetMode = PixelOffsetMode.HighQuality;
graphicsResult.DrawImage(sourceBitmap,
new Rectangle(0, 0,
bitmapResult.Width, bitmapResult.Height),
new Rectangle(0, 0,
sourceBitmap.Width, sourceBitmap.Height),
GraphicsUnit.Pixel);
graphicsResult.Flush();
return bitmapResult;
public static Bitmap MedianFilter(this Bitmap sourceBitmap,
int matrixSize,
int bias = 0,
bool grayscale = false)
BitmapData sourceData =
sourceBitmap.LockBits(new Rectangle(0, 0,
sourceBitmap.Width, sourceBitmap.Height),
ImageLockMode.ReadOnly,
PixelFormat.Format32bppArgb);
byte[] pixelBuffer = new byte[sourceData.Stride *
sourceData.Height];
byte[] resultBuffer = new byte[sourceData.Stride *
sourceData.Height];
Marshal.Copy(sourceData.Scan0, pixelBuffer, 0,
pixelBuffer.Length);
sourceBitmap.UnlockBits(sourceData);
if (grayscale == true)
float rgb = 0;
for (int k = 0; k < pixelBuffer.Length; k += 4)
rgb = pixelBuffer[k] * 0.11f;
rgb += pixelBuffer[k + 1] * 0.59f;
rgb += pixelBuffer[k + 2] * 0.3f;
pixelBuffer[k] = (byte)rgb;
pixelBuffer[k + 1] = pixelBuffer[k];
pixelBuffer[k + 2] = pixelBuffer[k];
pixelBuffer[k + 3] = 255;
int filterOffset = (matrixSize - 1) / 2;
int calcOffset = 0;
int byteOffset = 0;
List<int> neighbourPixels = new List<int>();
byte[] middlePixel;
for (int offsetY = filterOffset; offsetY <
sourceBitmap.Height - filterOffset; offsetY++)
for (int offsetX = filterOffset; offsetX <
sourceBitmap.Width - filterOffset; offsetX++)
byteOffset = offsetY *
sourceData.Stride +
offsetX * 4;
neighbourPixels.Clear();
for (int filterY = -filterOffset;
filterY <= filterOffset; filterY++)
for (int filterX = -filterOffset;
filterX <= filterOffset; filterX++)
calcOffset = byteOffset +
(filterX * 4) +
(filterY * sourceData.Stride);
neighbourPixels.Add(BitConverter.ToInt32(
pixelBuffer, calcOffset));
neighbourPixels.Sort();
middlePixel = BitConverter.GetBytes(
neighbourPixels[filterOffset]);
resultBuffer[byteOffset] = middlePixel[0];
resultBuffer[byteOffset + 1] = middlePixel[1];
resultBuffer[byteOffset + 2] = middlePixel[2];
resultBuffer[byteOffset + 3] = middlePixel[3];
Bitmap resultBitmap = new Bitmap(sourceBitmap.Width,
sourceBitmap.Height);
BitmapData resultData =
resultBitmap.LockBits(new Rectangle(0, 0,
resultBitmap.Width, resultBitmap.Height),
ImageLockMode.WriteOnly,
PixelFormat.Format32bppArgb);
Marshal.Copy(resultBuffer, 0, resultData.Scan0,
resultBuffer.Length);
resultBitmap.UnlockBits(resultData);
return resultBitmap;
FrmPhoto 类 ---------------------------------------How the GUI Looks
public partial class FrmPhoto : Form
private Bitmap originalBitmap = null;
private Bitmap previewBitmap = null;
private Bitmap resultBitmap = null;
public FrmPhoto()
InitializeComponent();
cmbEdge.SelectedIndex = 0;
private void btnOpen_Click(object sender, EventArgs e)
OpenFileDialog dialog = new OpenFileDialog();
dialog.Title = "Select an image file.";
dialog.Filter = "Png Images(*.png)|*.png|Jpeg Images(*.jpg)|*.jpg";
dialog.Filter += "|Bitmap Images(*.bmp)|*.bmp";
if (dialog.ShowDialog() == DialogResult.OK)
StreamReader streamReader = new StreamReader(dialog.FileName);
originalBitmap = (Bitmap)Bitmap.FromStream(streamReader.BaseStream);
streamReader.Close();
previewBitmap = originalBitmap.CopyToSquareCanvas(pix1.Width);
pix1.Image = previewBitmap;
private void ApplyFilter(bool preview)
if (previewBitmap == null || cmbEdge.SelectedIndex == -1)
return;
Bitmap selectedSource = null;
Bitmap bitmapResult = null;
if (preview == true)
selectedSource = previewBitmap;
else
selectedSource = originalBitmap;
if (selectedSource != null)
if (cmbEdge.SelectedItem.ToString() == "None")
bitmapResult = selectedSource;
else if (cmbEdge.SelectedItem.ToString() == "Median 3x3")
bitmapResult = selectedSource.MedianFilter(3);
else if (cmbEdge.SelectedItem.ToString() == "Median 5x5")
bitmapResult = selectedSource.MedianFilter(5);
else if (cmbEdge.SelectedItem.ToString() == "Median 7x7")
bitmapResult = selectedSource.MedianFilter(7);
else if (cmbEdge.SelectedItem.ToString() == "Median 9x9")
bitmapResult = selectedSource.MedianFilter(9);
else if (cmbEdge.SelectedItem.ToString() == "Median 11x11")
bitmapResult = selectedSource.MedianFilter(11);
else if (cmbEdge.SelectedItem.ToString() == "Median 13x13")
bitmapResult = selectedSource.MedianFilter(13);
if (bitmapResult != null)
if (preview == true)
pix1.Image = bitmapResult;
else
resultBitmap = bitmapResult;
private void button1_Click(object sender, EventArgs e)
ApplyFilter(true);
【问题讨论】：
【参考方案1】：我们可以使用Parallel.For 方法为我们进行并行化。
我们必须让所有在并行循环中被修改的变量都是本地的。
int filterOffset = (matrixSize - 1) / 2;
//int calcOffset = 0;
//int byteOffset = 0;
//List<int> neighbourPixels = new List<int>();
//byte[] middlePixel;
var w = sourceBitmap.Width - filterOffset;
for (int offsetY = filterOffset; offsetY < sourceBitmap.Height - filterOffset; offsetY++)
Parallel.For(filterOffset, w, offsetX =>
var byteOffset = offsetY * sourceData.Stride + offsetX * 4; // local
var neighbourPixels = new List<int>(); // local
//neighbourPixels.Clear();
for (int filterY = -filterOffset; filterY <= filterOffset; filterY++)
for (int filterX = -filterOffset; filterX <= filterOffset; filterX++)
var calcOffset = byteOffset + (filterX * 4) + (filterY * sourceData.Stride); // local
neighbourPixels.Add(BitConverter.ToInt32(pixelBuffer, calcOffset));
neighbourPixels.Sort();
var middlePixel = BitConverter.GetBytes(neighbourPixels[filterOffset]); // local
resultBuffer[byteOffset] = middlePixel[0];
resultBuffer[byteOffset + 1] = middlePixel[1];
resultBuffer[byteOffset + 2] = middlePixel[2];
resultBuffer[byteOffset + 3] = middlePixel[3];
);
;
这使我的机器的性能提高了两倍以上（2 个物理内核，4 个逻辑内核）。
外循环的并行化肯定会带来更多的加速。但是，让它变得更加困难。
以类似的方式，可以对灰度滤镜进行并行化。
【讨论】：
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