加快Bitmap的訪問速度
引言
在對Bitmap圖片操做的時候，有時須要用到獲取或設置像素顏色方法：GetPixel 和 SetPixel，安全
若是直接對這兩個方法進行操做的話速度很慢，這裏咱們能夠經過把數據提取出來操做，而後操做完在複製回去能夠加快訪問速度ide
兩種方法
其實對Bitmap的訪問還有兩種方式，一種是內存法，一種是指針法this
一、內存法spa
這裏定義一個類LockBitmap，經過把Bitmap數據拷貝出來，在內存上直接操做，操做完成後在拷貝到Bitmap中指針
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：先鎖定Bitmap，而後經過Pixels操做顏色對象，最後釋放鎖，把數據更新到Bitmap中code
string file = @"C:\test.jpg";
Bitmap bmp = new Bitmap(Image.FromFile(file));
LockBitmap lockbmp = new LockBitmap(bmp);
//鎖定Bitmap，經過Pixel訪問顏色
lockbmp.LockBits();
//獲取顏色
Color color = lockbmp.GetPixel(10, 10);
//從內存解鎖Bitmap
lockbmp.UnlockBits();
二、指針法component
這種方法訪問速度比內存法更快，直接經過指針對內存進行操做，不須要進行拷貝，可是在C#中直接經過指針操做內存是不安全的，因此須要在代碼中加入unsafe關鍵字，在生成選項中把容許不安全代碼勾上，才能編譯經過orm
這裏定義成PointerBitmap類對象
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);
//獲得首地址
unsafe
{
Iptr = bitmapData.Scan0;
//二維圖像循環
}
}
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;
}
}
}
}
使用方法這裏就不列出來了，跟上面的LockBitmap相似blog
資料
http://www.codeproject.com/Tips/240428/Work-with-bitmap-faster-with-Csharp
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