谷歌百度以图搜图 "感知哈希算法" C#简单实现

 

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/// <summary> /// 感知哈希算法 /// </summary> public class ImageComparer {           /// <summary>     /// 获取图片的Hashcode     /// </summary>     /// <param name="imageName"></param>     /// <returns></returns>     public static string GetImageHashCode(string imageName)     {         int width = 8;         int height = 8;           //  第一步         //  将图片缩小到8x8的尺寸，总共64个像素。这一步的作用是去除图片的细节，         //  只保留结构、明暗等基本信息，摒弃不同尺寸、比例带来的图片差异。         Bitmap bmp = new Bitmap(Thumb(imageName));         int[] pixels = new int[width * height];           //  第二步         //  将缩小后的图片，转为64级灰度。也就是说，所有像素点总共只有64种颜色。         for (int i = 0; i < width; i++)         {             for (int j = 0; j < height; j++)             {                 Color color = bmp.GetPixel(i, j);                 pixels[i * height + j] = RGBToGray(color.ToArgb());             }         }           //  第三步         //  计算所有64个像素的灰度平均值。         int avgPixel = Average(pixels);           //  第四步         //  将每个像素的灰度，与平均值进行比较。大于或等于平均值，记为1；小于平均值，记为0。         int[] comps = new int[width * height];         for (int i = 0; i < comps.Length; i++)         {             if (pixels[i] >= avgPixel)             {                 comps[i] = 1;             }             else             {                 comps[i] = 0;             }         }           //  第五步         //  将上一步的比较结果，组合在一起，就构成了一个64位的整数，这就是这张图片的指纹。组合的次序并不重要，只要保证所有图片都采用同样次序就行了。         StringBuilder hashCode = new StringBuilder();         for (int i = 0; i < comps.Length; i += 4)         {             int result = comps[i] * (int)Math.Pow(2, 3) + comps[i + 1] * (int)Math.Pow(2, 2) + comps[i + 2] * (int)Math.Pow(2, 1) + comps[i + 2];             hashCode.Append(BinaryToHex(result));         }         bmp.Dispose();         return hashCode.ToString();     }       /// <summary>     /// 计算"汉明距离"（Hamming distance）。     /// 如果不相同的数据位不超过5，就说明两张图片很相似；如果大于10，就说明这是两张不同的图片。     /// </summary>     /// <param name="sourceHashCode"></param>     /// <param name="hashCode"></param>     /// <returns></returns>     public static int HammingDistance(String sourceHashCode, String hashCode)     {         int difference = 0;         int len = sourceHashCode.Length;           for (int i = 0; i < len; i++)         {             if (sourceHashCode[i] != hashCode[i])             {                 difference++;             }         }         return difference;     }       /// <summary>     /// 缩放图片     /// </summary>     /// <param name="imageName"></param>     /// <returns></returns>     private static Image Thumb(string imageName)     {         return Image.FromFile(imageName).GetThumbnailImage(8, 8, () => { return false; }, IntPtr.Zero);     }       /// <summary>     /// 转为64级灰度     /// </summary>     /// <param name="pixels"></param>     /// <returns></returns>     private static int RGBToGray(int pixels)     {         int _red = (pixels >> 16) & 0xFF;         int _green = (pixels >> 8) & 0xFF;         int _blue = (pixels) & 0xFF;         return (int)(0.3 * _red + 0.59 * _green + 0.11 * _blue);     }       /// <summary>     /// 计算平均值     /// </summary>     /// <param name="pixels"></param>     /// <returns></returns>     private static int Average(int[] pixels)     {         float m = 0;         for (int i = 0; i < pixels.Length; ++i)         {             m += pixels[i];         }         m = m / pixels.Length;         return (int)m;     }       private static char BinaryToHex(int binary)     {         char ch = ' ';         switch (binary)         {             case 0:                 ch = '0';                 break;             case 1:                 ch = '1';                 break;             case 2:                 ch = '2';                 break;             case 3:                 ch = '3';                 break;             case 4:                 ch = '4';                 break;             case 5:                 ch = '5';                 break;             case 6:                 ch = '6';                 break;             case 7:                 ch = '7';                 break;             case 8:                 ch = '8';                 break;             case 9:                 ch = '9';                 break;             case 10:                 ch = 'a';                 break;             case 11:                 ch = 'b';                 break;             case 12:                 ch = 'c';                 break;             case 13:                 ch = 'd';                 break;             case 14:                 ch = 'e';                 break;             case 15:                 ch = 'f';                 break;             default:                 ch = ' ';                 break;         }         return ch;     } }