【C#】加快Bitmap的访问速度
摘自：http://www.codeproject.com/Tips/240428/Work-with-bitmap-faster-with-Csharp#_rating
在对Bitmap图片操作的时候，有时需要用到获取或设置像素颜色方法：GetPixel 和 SetPixel，
如果直接对这两个方法进行操作的话速度很慢，这里我们可以通过把数据提取出来操作，然后操作完在复制回去可以加快访问速度
其实对Bitmap的访问还有两种方式，一种是内存法，一种是指针法
1、内存法
这里定义一个类LockBitmap，通过把Bitmap数据拷贝出来，在内存上直接操作，操作完成后在拷贝到Bitmap中
public class LockBitmap { Bitmap source = null; IntPtr Iptr = IntPtr.Zero; BitmapData bitmapData = null; public byte[] Pixels { get; set; } public int Depth { get; private set; } public int Width { get; private set; } public int Height { get; private set; } public LockBitmap(Bitmap source) { this.source = source; } /// <summary> /// Lock bitmap data /// </summary> public void LockBits() { try { // Get width and height of bitmap Width = source.Width; Height = source.Height; // get total locked pixels count int PixelCount = Width * Height; // Create rectangle to lock Rectangle rect = new Rectangle(0, 0, Width, Height); // get source bitmap pixel format size Depth = System.Drawing.Bitmap.GetPixelFormatSize(source.PixelFormat); // Check if bpp (Bits Per Pixel) is 8, 24, or 32 if (Depth != 8 && Depth != 24 && Depth != 32) { throw new ArgumentException("Only 8, 24 and 32 bpp images are supported."); } // Lock bitmap and return bitmap data bitmapData = source.LockBits(rect, ImageLockMode.ReadWrite, source.PixelFormat); // create byte array to copy pixel values int step = Depth / 8; Pixels = new byte[PixelCount * step]; Iptr = bitmapData.Scan0; // Copy data from pointer to array Marshal.Copy(Iptr, Pixels, 0, Pixels.Length); } catch (Exception ex) { throw ex; } } /// <summary> /// Unlock bitmap data /// </summary> public void UnlockBits() { try { // Copy data from byte array to pointer Marshal.Copy(Pixels, 0, Iptr, Pixels.Length); // Unlock bitmap data source.UnlockBits(bitmapData); } catch (Exception ex) { throw ex; } } /// <summary> /// Get the color of the specified pixel /// </summary> /// <param name="x"></param> /// <param name="y"></param> /// <returns></returns> public Color GetPixel(int x, int y) { Color clr = Color.Empty; // Get color components count int cCount = Depth / 8; // Get start index of the specified pixel int i = ((y * Width) + x) * cCount; if (i > Pixels.Length - cCount) throw new IndexOutOfRangeException(); if (Depth == 32) // For 32 bpp get Red, Green, Blue and Alpha { byte b = Pixels[i]; byte g = Pixels[i + 1]; byte r = Pixels[i + 2]; byte a = Pixels[i + 3]; // a clr = Color.FromArgb(a, r, g, b); } if (Depth == 24) // For 24 bpp get Red, Green and Blue { byte b = Pixels[i]; byte g = Pixels[i + 1]; byte r = Pixels[i + 2]; clr = Color.FromArgb(r, g, b); } if (Depth == 8) // For 8 bpp get color value (Red, Green and Blue values are the same) { byte c = Pixels[i]; clr = Color.FromArgb(c, c, c); } return clr; } /// <summary> /// Set the color of the specified pixel /// </summary> /// <param name="x"></param> /// <param name="y"></param> /// <param name="color"></param> public void SetPixel(int x, int y, Color color) { // Get color components count int cCount = Depth / 8; // Get start index of the specified pixel int i = ((y * Width) + x) * cCount; if (Depth == 32) // For 32 bpp set Red, Green, Blue and Alpha { Pixels[i] = color.B; Pixels[i + 1] = color.G; Pixels[i + 2] = color.R; Pixels[i + 3] = color.A; } if (Depth == 24) // For 24 bpp set Red, Green and Blue { Pixels[i] = color.B; Pixels[i + 1] = color.G; Pixels[i + 2] = color.R; } if (Depth == 8) // For 8 bpp set color value (Red, Green and Blue values are the same) { Pixels[i] = color.B; } } }
使用：先锁定Bitmap，然后通过Pixels操作颜色对象，最后释放锁，把数据更新到Bitmap中
string file = @"C:\test.jpg"; Bitmap bmp = new Bitmap(Image.FromFile(file)); LockBitmap lockbmp = new LockBitmap(bmp); //锁定Bitmap，通过Pixel访问颜色 lockbmp.LockBits(); //获取颜色 Color color = lockbmp.GetPixel(10, 10); //从内存解锁Bitmap lockbmp.UnlockBits();
2、指针法
这种方法访问速度比内存法更快，直接通过指针对内存进行操作，不需要进行拷贝，但是在C#中直接通过指针操作内存是不安全的，所以需要在代码中加入unsafe关键字，在生成选项中把允许不安全代码勾上，才能编译通过
这里定义成PointerBitmap类
public class PointBitmap { Bitmap source = null; IntPtr Iptr = IntPtr.Zero; BitmapData bitmapData = null; public int Depth { get; private set; } public int Width { get; private set; } public int Height { get; private set; } public PointBitmap(Bitmap source) { this.source = source; } public void LockBits() { try { // Get width and height of bitmap Width = source.Width; Height = source.Height; // get total locked pixels count int PixelCount = Width * Height; // Create rectangle to lock Rectangle rect = new Rectangle(0, 0, Width, Height); // get source bitmap pixel format size Depth = System.Drawing.Bitmap.GetPixelFormatSize(source.PixelFormat); // Check if bpp (Bits Per Pixel) is 8, 24, or 32 if (Depth != 8 && Depth != 24 && Depth != 32) { throw new ArgumentException("Only 8, 24 and 32 bpp images are supported."); } // Lock bitmap and return bitmap data bitmapData = source.LockBits(rect, ImageLockMode.ReadWrite, source.PixelFormat); //得到首地址 unsafe { Iptr = bitmapData.Scan0; //二维图像循环 } } catch (Exception ex) { throw ex; } } public void UnlockBits() { try { source.UnlockBits(bitmapData); } catch (Exception ex) { throw ex; } } public Color GetPixel(int x, int y) { unsafe { byte* ptr = (byte*)Iptr; ptr = ptr + bitmapData.Stride * y; ptr += Depth * x / 8; Color c = Color.Empty; if (Depth == 32) { int a = ptr[3]; int r = ptr[2]; int g = ptr[1]; int b = ptr[0]; c = Color.FromArgb(a, r, g, b); } else if (Depth == 24) { int r = ptr[2]; int g = ptr[1]; int b = ptr[0]; c = Color.FromArgb(r, g, b); } else if (Depth == 8) { int r = ptr[0]; c = Color.FromArgb(r, r, r); } return c; } } public void SetPixel(int x, int y, Color c) { unsafe { byte* ptr = (byte*)Iptr; ptr = ptr + bitmapData.Stride * y; ptr += Depth * x / 8; if (Depth == 32) { ptr[3] = c.A; ptr[2] = c.R; ptr[1] = c.G; ptr[0] = c.B; } else if (Depth == 24) { ptr[2] = c.R; ptr[1] = c.G; ptr[0] = c.B; } else if (Depth == 8) { ptr[2] = c.R; ptr[1] = c.G; ptr[0] = c.B; } } } }
使用方法这里就不列出来了，跟上面的LockBitmap类似
