直方圖匹配，又稱直方圖規定化，即變換原圖的直方圖為規定的某種形式的直方圖，從而使兩幅圖像具有類似的色調和反差。直方圖匹配屬於非線性點運算。
直方圖規定化的原理：對兩個直方圖都做均衡化，變成相同的歸一化的均勻直方圖，以此均勻直方圖為媒介，再對參考圖像做均衡化的逆運算
/// <summary> /// 直方圖匹配 /// </summary> /// <param name="srcBmp">原始圖像</param> /// <param name="matchingBmp">匹配圖像</param> /// <param name="dstBmp">處理后圖像</param> /// <returns>處理成功 true 失敗 false</returns> public static bool HistogramMatching(Bitmap srcBmp, Bitmap matchingBmp, out Bitmap dstBmp) { if (srcBmp == null || matchingBmp == null) { dstBmp = null; return false; } dstBmp = new Bitmap(srcBmp); Bitmap tempSrcBmp = new Bitmap(srcBmp); Bitmap tempMatchingBmp = new Bitmap(matchingBmp); double[] srcCpR = null; double[] srcCpG = null; double[] srcCpB = null; double[] matchCpB = null; double[] matchCpG = null; double[] matchCpR = null; //分別計算兩幅圖像的累計概率分布 getCumulativeProbabilityRGB(tempSrcBmp, out srcCpR, out srcCpG, out srcCpB); getCumulativeProbabilityRGB(tempMatchingBmp, out matchCpR, out matchCpG, out matchCpB); double diffAR = 0, diffBR = 0, diffAG = 0, diffBG = 0, diffAB = 0, diffBB = 0; byte kR = 0, kG = 0, kB = 0; //逆映射函數 byte[] mapPixelR = new byte[256]; byte[] mapPixelG = new byte[256]; byte[] mapPixelB = new byte[256]; //分別計算RGB三個分量的逆映射函數 //R for (int i = 0; i < 256; i++) { diffBR = 1; for (int j = kR; j < 256; j++) { //找到兩個累計分布函數中最相似的位置 diffAR = Math.Abs(srcCpR[i] - matchCpR[j]); if (diffAR - diffBR < 1.0E-08) {//當兩概率之差小於0.000000001時可近似認為相等 diffBR = diffAR; //記錄下此時的灰度級 kR = (byte)j; } else { kR = (byte)Math.Abs(j - 1); break; } } if (kR == 255) { for (int l = i; l < 256; l++) { mapPixelR[l] = kR; } break; } mapPixelR[i] = kR; } //G for (int i = 0; i < 256; i++) { diffBG = 1; for (int j = kG; j < 256; j++) { diffAG = Math.Abs(srcCpG[i] - matchCpG[j]); if (diffAG - diffBG < 1.0E-08) { diffBG = diffAG; kG = (byte)j; } else { kG = (byte)Math.Abs(j - 1); break; } } if (kG == 255) { for (int l = i; l < 256; l++) { mapPixelG[l] = kG; } break; } mapPixelG[i] = kG; } //B for (int i = 0; i < 256; i++) { diffBB = 1; for (int j = kB; j < 256; j++) { diffAB = Math.Abs(srcCpB[i] - matchCpB[j]); if (diffAB - diffBB < 1.0E-08) { diffBB = diffAB; kB = (byte)j; } else { kB = (byte)Math.Abs(j - 1); break; } } if (kB == 255) { for (int l = i; l < 256; l++) { mapPixelB[l] = kB; } break; } mapPixelB[i] = kB; } //映射變換 BitmapData bmpData = dstBmp.LockBits(new Rectangle(0, 0, dstBmp.Width, dstBmp.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb); unsafe { byte* ptr = null; for (int i = 0; i < dstBmp.Height; i++) { ptr = (byte*)bmpData.Scan0 + i * bmpData.Stride; for (int j = 0; j < dstBmp.Width; j++) { ptr[j * 3 + 2] = mapPixelR[ptr[j * 3 + 2]]; ptr[j * 3 + 1] = mapPixelG[ptr[j * 3 + 1]]; ptr[j * 3] = mapPixelB[ptr[j * 3]]; } } } dstBmp.UnlockBits(bmpData); return true; } /// <summary> /// 計算各個圖像分量的累計概率分布 /// </summary> /// <param name="srcBmp">原始圖像</param> /// <param name="cpR">R分量累計概率分布</param> /// <param name="cpG">G分量累計概率分布</param> /// <param name="cpB">B分量累計概率分布</param> private static void getCumulativeProbabilityRGB(Bitmap srcBmp, out double[] cpR, out double[] cpG, out double[] cpB) { if (srcBmp == null) { cpB = cpG = cpR = null; return; } cpR = new double[256]; cpG = new double[256]; cpB = new double[256]; int[] hR = null; int[] hG = null; int[] hB = null; double[] tempR = new double[256]; double[] tempG = new double[256]; double[] tempB = new double[256]; getHistogramRGB(srcBmp, out hR, out hG, out hB); int totalPxl = srcBmp.Width * srcBmp.Height; for (int i = 0; i < 256; i++) { if (i != 0) { tempR[i] = tempR[i - 1] + hR[i]; tempG[i] = tempG[i - 1] + hG[i]; tempB[i] = tempB[i - 1] + hB[i]; } else { tempR[0] = hR[0]; tempG[0] = hG[0]; tempB[0] = hB[0]; } cpR[i] = (tempR[i] / totalPxl); cpG[i] = (tempG[i] / totalPxl); cpB[i] = (tempB[i] / totalPxl); } } /// <summary> /// 獲取圖像三個分量的直方圖數據 /// </summary> /// <param name="srcBmp">圖像</param> /// <param name="hR">R分量直方圖數據</param> /// <param name="hG">G分量直方圖數據</param> /// <param name="hB">B分量直方圖數據</param> public static void getHistogramRGB(Bitmap srcBmp, out int[] hR, out int[] hG, out int[] hB) { if (srcBmp == null) { hR = hB = hG = null; return; } hR = new int[256]; hB = new int[256]; hG = new int[256]; BitmapData bmpData = srcBmp.LockBits(new Rectangle(0, 0, srcBmp.Width, srcBmp.Height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb); unsafe { byte* ptr = null; for (int i = 0; i < srcBmp.Height; i++) { ptr = (byte*)bmpData.Scan0 + i * bmpData.Stride; for (int j = 0; j < srcBmp.Width; j++) { hB[ptr[j * 3]]++; hG[ptr[j * 3 + 1]]++; hR[ptr[j * 3 + 2]]++; } } } srcBmp.UnlockBits(bmpData); return; }
