图象处理算法(六)

六、对比度
　　扫描图像，找到图像明度的最大最小值，将max映射为255或250等较大值，min映射到0或5等较小值，重新计算各点的明度。

 1        public static bool Contrast(Bitmap b, int Lavel)
 2        {
 3            if (Lavel < -100) return false;
 4            if (Lavel >  255) return false;
 5
 6            BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), 
 7                ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
 8
 9            double pixel = 0, contrast = (100.0 + Lavel) / 100.0;
10            contrast *= contrast;
11
12            int stride = bmData.Stride;
13            System.IntPtr Scan0 = bmData.Scan0;
14
15            unsafe
16            {
17                byte *p = (byte *)(void *)Scan0;
18                int red, green, blue;
19                int nOffset = stride - b.Width*3;
20
21                for(int y = 0; y < b.Height; ++y)
22                {
23                    for(int x = 0; x < b.Width; ++x )
24                    {
25                        blue = p[0];
26                        green = p[1];
27                        red = p[2];
28
29                        pixel = blue / 255.0;
30                        pixel -= 0.5;
31                        pixel *= contrast;
32                        pixel += 0.5;
33                        pixel *= 255;
34                        if (pixel < 0) pixel = 0;
35                        if (pixel > 255) pixel = 255;
36                        p[0] = (byte) pixel;     
37   
38                        pixel = green / 255.0;
39                        pixel -= 0.5;
40                        pixel *= contrast;
41                        pixel += 0.5;
42                        pixel *= 255;
43                        if (pixel < 0) pixel = 0;
44                        if (pixel > 255) pixel = 255;
45                        p[1] = (byte) pixel;
46 
47                        pixel = red / 255.0;
48                        pixel -= 0.5;
49                        pixel *= contrast;
50                        pixel += 0.5;
51                        pixel *= 255;
52                        if (pixel < 0) pixel = 0;
53                        if (pixel > 255) pixel = 255;
54                        p[2] = (byte) pixel;
55
56                        p += 3;
57                    }
58                    p += nOffset;
59                }
60            }
61            b.UnlockBits(bmData);
62            return true;
63        }