互信息

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互信息

在做医学图像分割时需要用到互信息来计算两幅图像的相似度。之前写好了函数，在此备份。

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float MI_hhl(float ***Img1, float ***Img2, int Image_X_Size, int Image_Y_Size, int Image_Z_Size)
{
	//绘制直方图
	int Hist_Img1[256], Hist_Img2[256];
	for (int t = 0; t < 256; t++)
	{
		Hist_Img1[t] = 0;
		Hist_Img2[t] = 0;
	}
	for (int k = 0; k < Image_Z_Size; k++)
	{
		for (int i = 0; i < Image_X_Size; i++)
		{
			for (int j = 0; j<Image_Y_Size; j++)
			{
				Hist_Img1[(int)Img1[k][i][j]]++;
				Hist_Img2[(int)Img2[k][i][j]]++;
			}
		}
	}
	//绘制两个图像的联合直方图
	int Hist[256][256];
	for (int i = 0; i < 256; i++)
	{
		for (int j = 0; j < 256; j++)
		{
			Hist[i][j] = 0;
		}
	}
	for (int k = 0; k < Image_Z_Size; k++)
	{
		for (int i = 0; i < Image_X_Size; i++)
		{
			for (int j = 0; j<Image_Y_Size; j++)
			{
				Hist[(int)Img1[k][i][j]][(int)Img2[k][i][j]]++;
			}
		}
	}

	//计算单个概率
	float P_Img1[256], P_Img2[256];
	float all_number;
	all_number = Image_X_Size * Image_Y_Size * Image_Z_Size;
	for (int t = 0; t < 256; t++)
	{
		P_Img1[t] = (float)Hist_Img1[t] / all_number;
		P_Img2[t] = (float)Hist_Img2[t] / all_number;
	}

	//计算联合概率
	float P_Hist[256][256];
	for (int i = 0; i < 256; i++)
	{
		for (int j = 0; j < 256; j++)
		{
			P_Hist[i][j] = (float)Hist[i][j] / all_number;
		}
	}

	//计算两个图像的互信息
	float Mut_INF = 0;
	for (int i = 0; i < 256; i++)
	{
		for (int j = 0; j < 256; j++)
		{
			if (P_Hist[i][j] == 0 || P_Img1[i] == 0 || P_Img2[j] == 0)
			{
				continue;
			}
			Mut_INF += P_Hist[i][j] * log10(P_Hist[i][j] / (P_Img1[i] * P_Img2[j]));
		}
	}

	return Mut_INF;
}