加快Bitmap的访问速度
引言
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
两种方法
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
资料
http://www.codeproject.com/Tips/240428/Work-with-bitmap-faster-with-Csharp