C# 画8位彩色图片（自定义调色板）

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此方法参照msdn上的画8位灰阶gif图片的方法。 
函数1,2为画自定义彩色图片方法。
函数3（GetColorPalette）和函数4（SaveGIFWithNewGrayscale）为msdn原方法。

 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Drawing;
using System.Drawing.Imaging;

namespace Em_Picture
{
    class Class2
    {
        public static List<Color> cl;
        //函数1：
        //此为原创，转帖请加链接（http://www.cnblogs.com/wdh1983/admin/EditPosts.aspx?postid=1378468）！
        static void DrawPicture()
        {
            Image image = Image.FromFile("加载你的图片：比如一个总共11色的股票行情走势图，其白色为背景色");
            //获取11色相对应的调色板
            ColorPalette pal = GetColorPalette(11);
            //列出图片中所包含的颜色
            cl = new List<Color>();
            cl.Add(Color.FromArgb(255, 0,   0,   0  ));
            cl.Add(Color.FromArgb(255, 255, 0,   0  ));
            cl.Add(Color.FromArgb(255, 51,  51,  102));
            cl.Add(Color.FromArgb(255, 102, 102, 102));
            cl.Add(Color.FromArgb(255, 0,   128, 0  ));
            cl.Add(Color.FromArgb(255, 128, 128, 128));
            cl.Add(Color.FromArgb(255, 206, 158, 0  ));
            cl.Add(Color.FromArgb(255, 200, 200, 200));
            cl.Add(Color.FromArgb(255, 206, 206, 206));
            cl.Add(Color.FromArgb(255, 206, 207, 156));
            cl.Add(Color.FromArgb(255, 255, 255, 255));
            //重写调色板前11色
            for (int i = 0; i < cl.Count; i++)
            {
                pal.Entries[i] = cl[i];
            }
            pal.Entries[10] = Color.FromArgb(0, 255, 255, 255); // 将其alpha值修改为0，可使背景通透
            //调用画8位彩色图函数
            SaveGIFWithNewColorTable(image, pal, "你要保存新图片的位置");
        }
        //函数2：
        //此为原创，转帖请加链接（http://www.cnblogs.com/wdh1983/admin/EditPosts.aspx?postid=1378468）！
        public static void SaveGIFWithNewColorTable(Image image, ColorPalette pal, string filename)
        {
            int Width = image.Width;
            int Height = image.Height;
            Bitmap bitmap = new Bitmap(Width, Height, PixelFormat.Format8bppIndexed);
            bitmap.Palette = pal;
            Bitmap BmpCopy = new Bitmap(Width, Height, PixelFormat.Format32bppArgb);
            {
                Graphics g = Graphics.FromImage(BmpCopy);
                g.PageUnit = GraphicsUnit.Pixel;
                g.DrawImage(image, 0, 0, Width, Height);
                g.Dispose();
            }
            BitmapData bitmapData;
            Rectangle rect = new Rectangle(0, 0, Width, Height);
            bitmapData = bitmap.LockBits(rect, ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);
            IntPtr pixels = bitmapData.Scan0;
            BitmapData bmData = BmpCopy.LockBits(rect, ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);
            unsafe
            {
                byte* pBits;
                if (bitmapData.Stride > 0)
                    pBits = (byte*)pixels.ToPointer();
                else
                    pBits = (byte*)pixels.ToPointer() + bitmapData.Stride * (Height - 1);
                uint stride = (uint)Math.Abs(bitmapData.Stride);
                //
                byte* p = (byte*)bmData.Scan0;
                int offset = bmData.Stride - Width * 4;
                //
                for (uint row = 0; row < Height; ++row)
                {
                    for (uint col = 0; col < Width; ++col)
                    {
                        //取原图中某个点颜色值
                        Color pixel = Color.FromArgb(p[3], p[2], p[1], p[0]);
                        p += 4;
                        //获取新图对应点的指针
                        byte* p8bppPixel = pBits + row * stride + col;
                        //将原图这个点的颜色所对应的颜色索引值赋给指针
                        *p8bppPixel = (byte)cl.IndexOf(pixel);
                        
                        //===========================================================
                        //其实上面的代码比较消耗性能，改为如下代码较好（也可使用switch函数）
                        /*
                        byte b = 0;
                        //判断的顺序为建立颜色表的倒序
                        //因为白色为背景色，绝大多数判断到这里就会停止
                        if (p[1] == 255) b = 10;       
                        else if (p[1] == 207) b = 9;
                        else if (p[1] == 206) b = 8;
                        else if (p[1] == 200) b = 7;
                        else if (p[1] == 158) b = 6;
                        else if (p[1] == 128 && p[2] == 128) b = 5;
                        else if (p[1] == 128 && p[2] == 0) b = 4;
                        else if (p[1] == 102) b = 3;
                        else if (p[1] == 51) b = 2;
                        else if (p[1] == 0 && p[2] == 225) b = 1;
                        else if (p[1] == 0 && p[2] == 0) b = 0;
                        p += 4;
                        byte* p8bppPixel = pBits + row * stride + col;
                        *p8bppPixel = b;
                        */
                        //===========================================================
                    } /* end loop for col */
                    p += offset;
                } /* end loop for row */
                BmpCopy.UnlockBits(bmData);
            } /* end unsafe */
            bitmap.UnlockBits(bitmapData);
            bitmap.Save(filename, ImageFormat.Gif);
            BmpCopy.Dispose();
            bitmap.Dispose();
        }

        //函数3：获取颜色个数相对应的调色板         
        //此为原创，转帖请加链接（http://www.cnblogs.com/wdh1983/admin/EditPosts.aspx?postid=1378468）！
        public static ColorPalette GetColorPalette(uint nColors)
        {
            // Assume monochrome image.
            PixelFormat bitscolordepth = PixelFormat.Format1bppIndexed;
            ColorPalette palette;       // The Palette we are stealing
            Bitmap bitmap;              // The source of the stolen palette
            // Determine number of colors.
            if (nColors > 2)
                bitscolordepth = PixelFormat.Format4bppIndexed;
            if (nColors > 16)
                bitscolordepth = PixelFormat.Format8bppIndexed;
            // Make a new Bitmap object to get its Palette.
            bitmap = new Bitmap(1, 1, bitscolordepth);
            palette = bitmap.Palette;   // Grab the palette
            bitmap.Dispose();           // cleanup the source Bitmap
            return palette;             // Send the palette back
        }
        //函数4：画8位灰阶gif图
        //此为原创，转帖请加链接（http://www.cnblogs.com/wdh1983/admin/EditPosts.aspx?postid=1378468）！
        public static void SaveGIFWithNewGrayscale(Image image, string filename, uint nColors, bool fTransparent)
        {
            if (nColors > 256)
                nColors = 256;
            if (nColors < 2)
                nColors = 2;
            int Width = image.Width;
            int Height = image.Height;
            Bitmap bitmap = new Bitmap(Width, Height, PixelFormat.Format8bppIndexed);
            ColorPalette pal = GetColorPalette(nColors);
            for (uint i = 0; i < nColors; i++)
            {
                uint Alpha = 0xFF;                              // Colors are opaque.
                uint Intensity = i * 0xFF / (nColors - 1);      // Even distribution. 
                if (i == 0 && fTransparent)                     // Make this color index
                    Alpha = 0;                                  // Transparent
                pal.Entries[i] = Color.FromArgb((int)Alpha, (int)Intensity, (int)Intensity, (int)Intensity);
            }
            bitmap.Palette = pal;
            Bitmap BmpCopy = new Bitmap(Width, Height, PixelFormat.Format32bppArgb);
            {
                Graphics g = Graphics.FromImage(BmpCopy);
                g.PageUnit = GraphicsUnit.Pixel;
                g.DrawImage(image, 0, 0, Width, Height);
                g.Dispose();
            }
            BitmapData bitmapData;
            Rectangle rect = new Rectangle(0, 0, Width, Height);
            bitmapData = bitmap.LockBits(rect, ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);
            IntPtr pixels = bitmapData.Scan0;
            unsafe
            {
                byte* pBits;
                if (bitmapData.Stride > 0)
                    pBits = (byte*)pixels.ToPointer();
                else
                    pBits = (byte*)pixels.ToPointer() + bitmapData.Stride * (Height - 1);
                uint stride = (uint)Math.Abs(bitmapData.Stride);
                for (uint row = 0; row < Height; ++row)
                {
                    for (uint col = 0; col < Width; ++col)
                    {
                        Color pixel;        // The source pixel.
                        byte* p8bppPixel = pBits + row * stride + col;
                        pixel = BmpCopy.GetPixel((int)col, (int)row);
                        double luminance = (pixel.R * 0.299) + (pixel.G * 0.587) + (pixel.B * 0.114);
                        *p8bppPixel = (byte)(luminance * (nColors - 1) / 255 + 0.5);
                    } /* end loop for col */
                } /* end loop for row */
            } /* end unsafe */
            bitmap.UnlockBits(bitmapData);
            bitmap.Save(filename, ImageFormat.Gif);
            BmpCopy.Dispose();
            bitmap.Dispose();
        }
    }
}
此为原创，转帖请加链接（http://www.cnblogs.com/wdh1983/admin/EditPosts.aspx?postid=1378468）！