C# Bitmap图像处理(含增强对比度的三种方法)

/// <summary>
/// 像素点阵转换为bitmap
/// </summary>
/// <param name="rawValues">byte[]数组</param>
/// <param name="width">图片的宽度</param>
/// <param name="height">图片的高度</param>
/// <returns>bitmap图片</returns>
public static Bitmap ToGrayBitmap(byte[] rawValues, int width, int height)
{
    Bitmap bmp = new Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format8bppIndexed);
    BitmapData bmpData = bmp.LockBits(new System.Drawing.Rectangle(0, 0, width, height), ImageLockMode.WriteOnly, System.Drawing.Imaging.PixelFormat.Format8bppIndexed);
     获取图像参数  
    //bmpData.Stride = width;
    int stride = bmpData.Stride;  // 扫描线的宽度  
    int offset = stride - width;  // 显示宽度与扫描线宽度的间隙  
    IntPtr iptr = bmpData.Scan0;  // 获取bmpData的内存起始位置  
    int scanBytes = stride * height;// 用stride宽度，表示这是内存区域的大小  
     下面把原始的显示大小字节数组转换为内存中实际存放的字节数组  
    int posScan = 0, posReal = 0;// 分别设置两个位置指针，指向源数组和目标数组  
    byte[] pixelValues = new byte[scanBytes];  //为目标数组分配内存  
    for (int x = 0; x < height; x++)
    {
         下面的循环节是模拟行扫描  
        for (int y = 0; y < width; y++)
        {
            pixelValues[posScan++] = rawValues[posReal++];
        }
        posScan += offset;  //行扫描结束，要将目标位置指针移过那段“间隙”  
    }
     用Marshal的Copy方法，将刚才得到的内存字节数组复制到BitmapData中  
    System.Runtime.InteropServices.Marshal.Copy(pixelValues, 0, iptr, scanBytes);
    bmp.UnlockBits(bmpData);  // 解锁内存区域  
     下面的代码是为了修改生成位图的索引表，从伪彩修改为灰度  
    ColorPalette tempPalette;
    using (Bitmap tempBmp = new Bitmap(1, 1, System.Drawing.Imaging.PixelFormat.Format8bppIndexed))
    {
        tempPalette = tempBmp.Palette;
    }
    for (int i = 0; i < 256; i++)
    {
        tempPalette.Entries[i] = System.Drawing.Color.FromArgb(i, i, i);
    }
 
    bmp.Palette = tempPalette;
 
     算法到此结束，返回结果  
    return bmp;
}

//8位位图得到除去文件头信息的一位灰度数组
 
 
BitmapData bmpData = map.LockBits(new System.Drawing.Rectangle(0, 0, map.Width, map.Height), ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format8bppIndexed);
 
 获取图像参数  
 
int stride = bmpData.Stride;  // 扫描线的宽度  
 
int offset = stride - map.Width;  // 显示宽度与扫描线宽度的间隙  
 
IntPtr iptr = bmpData.Scan0;  // 获取bmpData的内存起始位置  
 
int scanBytes = stride * map.Height;// 用stride宽度，表示这是内存区域的大小  
 
 下面把原始的显示大小字节数组转换为内存中实际存放的字节数组  
 
mapdata = new byte[scanBytes];  //为目标数组分配内存
 
System.Runtime.InteropServices.Marshal.Copy(iptr, mapdata, 0, scanBytes); //copy内存中数据到数组中

 // 第一种方法：像素提取法。速度慢
        public Bitmap MethodBaseOnPixel(Bitmap bitmap,int degree)
        {
            Color curColor;
            int grayR, grayG, grayB;
 
            double Deg = (100.0 + degree) / 100.0;
            for (int i = 0; i < bitmap.Width; i++)
            {
                for (int j = 0; j < bitmap.Height; j++)
                {
                    curColor = bitmap.GetPixel(i, j);
                    grayR =Convert.ToInt32((((curColor.R / 255.0 - 0.5) * Deg + 0.5)) * 255);
                    grayG = Convert.ToInt32((((curColor.G / 255.0 - 0.5) * Deg + 0.5)) * 255);
                    grayB = Convert.ToInt32((((curColor.B / 255.0 - 0.5) * Deg + 0.5)) * 255);
                    if (grayR < 0)
                        grayR = 0;
                    else if (grayR > 255)
                        grayR = 255;
 
                    if (grayB < 0)
                        grayB = 0;
                    else if (grayB > 255)
                        grayB = 255;
 
                    if (grayG < 0)
                        grayG = 0;
                    else if (grayG > 255)
                        grayG = 255;
 
 
                    bitmap.SetPixel(i, j, Color.FromArgb(grayR, grayG, grayB));
                }
            }
 
            return bitmap;
        }

// 第二种方法：基于内存
        public unsafe Bitmap MethodBaseOnMemory(Bitmap bitmap, int degree)
        {
            if (bitmap == null)
            {
                return null;
            }
            double Deg = (100.0 + degree) / 100.0;
 
            int width = bitmap.Width;
            int height = bitmap.Height;
 
            int length = height * 3 * width;
            byte[] RGB = new byte[length];
 
            BitmapData data = bitmap.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
 
            System.IntPtr Scan0 = data.Scan0;
            System.Runtime.InteropServices.Marshal.Copy(Scan0, RGB, 0, length);
 
            double gray = 0;
            for (int i = 0; i < RGB.Length; i += 3)
            {
                for (int j = 0; j < 3; j++)
                {
                    gray = (((RGB[i + j] / 255.0 -0.5) * Deg+0.5)) * 255.0;
                    if (gray > 255)
                        gray = 255;
 
                    if (gray < 0)
                        gray = 0;
                    RGB[i + j] = (byte) gray;
                }
            }
 
            System.Runtime.InteropServices.Marshal.Copy(RGB, 0, Scan0, length);// 此处Copy是之前Copy的逆操作
            bitmap.UnlockBits(data);
            return bitmap;
        }
    }

//第三种方法：基于指针
        public unsafe Bitmap MethodBaseOnPtr(Bitmap b, int degree)
        {
            if (b == null)
            {
                return null;
            }
            try
            {
                double num = 0.0;
                double num2 = (100.0 + degree) / 100.0;
                num2 *= num2;
                int width = b.Width;
                int height = b.Height;
                BitmapData bitmapdata = b.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
                byte* numPtr = (byte*)bitmapdata.Scan0;
 
                int offset = bitmapdata.Stride - (width * 3);
                for (int i = 0; i < height; i++)
                {
                    for (int j = 0; j < width; j++)
                    {
                        for (int k = 0; k < 3; k++)
                        {
                            num = ((((((double)numPtr[k]) / 255.0) - 0.5) * num2) + 0.5) * 255.0;
                            if (num < 0.0)
                            {
                                num = 0.0;
                            }
                            if (num > 255.0)
                            {
                                num = 255.0;
                            }
                            numPtr[k] = (byte)num;
                        }
                        numPtr += 3;
 
                    }
                    numPtr += offset;
                }
                b.UnlockBits(bitmapdata);
                return b;
            }
            catch
            {
                return b;
            }
        }