最快的3x3中值模糊

10.1国庆后，知名博主：laviewpbt  http://www.cnblogs.com/Imageshop/

发起了一个优化3x3中值模糊的小活动。

俺也参加其中，今天博主laviewpbt  共享了一份不错的CLAHE代码。

free精神，真心为其点赞。

故俺也分享这份最快的3x3中值模糊的代码。

///	编写者： laviewpbt,  编写时间： 2015.10.16， 联系QQ: 33184777

/// <summary>
/// 快速的实现3*3大小的中值模糊,边缘1像素未做处理。（2015.10.12日）
/// </summary>
/// <param name="Src">原始数据。</param>
/// <param name="Dest">目标数据。</param>
/// 百度： Fast median search_ an ANSI C implementation.html
/// 优化版本: 落羽の殇  联系QQ:200759103

static unsigned int*    pixGreater = NULL;
static unsigned int*    pixLess = NULL;
static unsigned int cmpTable[256 * 256 * 2] = { 0 };
class  autoCmpTable
{
public:
	autoCmpTable() {
		unsigned int    x, y, p;
		unsigned int tableLength = 256 * 256;
		pixGreater = cmpTable;
		pixLess = cmpTable + tableLength;
		for (x = 0; x < 256; x++) {
			for (y = 0; y < 256; y++) {
				p = x + y * 256;
				if (x > y)
				{
					pixLess[p] = x;
					pixGreater[p] = y;
				}
				else
				{
					pixGreater[p] = x;
					pixLess[p] = y;
				}
			}
		}
	}
};
static  autoCmpTable initCmpTable;

IS_RET __stdcall Fastest33MedianBlur(TMatrix *Src, TMatrix *Dest)
{
	if (Src == NULL || Dest == NULL) return IS_RET_ERR_NULLREFERENCE;
	if (Src->Data == NULL || Dest->Data == NULL) return IS_RET_ERR_NULLREFERENCE;
	if (Src->Width != Dest->Width || Src->Height != Dest->Height || Src->Channel != Dest->Channel || Src->Depth != Dest->Depth || Src->WidthStep != Dest->WidthStep) return IS_RET_ERR_PARAMISMATCH;
	if (Src->Depth != IS_DEPTH_8U || Dest->Depth != IS_DEPTH_8U) return IS_RET_ERR_NOTSUPPORTED;
	IS_RET Ret = IS_RET_OK;

	if (!pixGreater&&!pixLess)
	{
		return IS_RET_ERR_NOTSUPPORTED;
	}
	if (Src->Data == Dest->Data)
	{
		TMatrix *Clone = NULL;
		Ret = IS_CloneMatrix(Src, &Clone);
		if (Ret != IS_RET_OK) return Ret;
		Ret = Fastest33MedianBlur(Clone, Dest);
		IS_FreeMatrix(&Clone);
		return Ret;
	}
	unsigned int X, Y, Width = Src->Width, Height = Src->Height;
	unsigned char *LineP0, *LineP1, *LineP2, *LinePD;
	unsigned int srcWidthStep = Src->WidthStep;
	unsigned int dstWidthStep = Dest->WidthStep;
	unsigned int srcChannel = Src->Channel;
	unsigned int dstChannel = Dest->Channel;
	unsigned char* SrcData = Src->Data;
	unsigned char* DstData = Dest->Data;

	if (srcChannel == 1)
	{
		unsigned    int Gray0, Gray1, Gray2, Gray3, Gray4, Gray5, Gray6, Gray7, Gray8, pos;
		for (Y = 1; Y < Height - 1; Y++)
		{
			LineP0 = SrcData + (Y - 1) * srcWidthStep + 1;
			LineP1 = LineP0 + srcWidthStep;
			LineP2 = LineP1 + srcWidthStep;
			LinePD = DstData + Y *dstWidthStep + 1;
			for (X = 1; X < Width - 1; X++)
			{
				Gray0 = LineP0[X - 1];
				Gray1 = LineP0[X];
				Gray2 = LineP0[X + 1];
				Gray3 = LineP1[X - 1];
				Gray4 = LineP1[X];
				Gray5 = LineP2[X + 1];
				Gray6 = LineP2[X - 1];
				Gray7 = LineP2[X];
				Gray8 = LineP2[X + 1];
				/*    if (Gray1 > Gray2) Swap(Gray1, Gray2);*/
				pos = Gray1 + Gray2 * 256;
				Gray2 = pixLess[pos];
				Gray1 = pixGreater[pos];
				/* if (Gray4 > Gray5) Swap(Gray4, Gray5);*/
				pos = Gray4 + Gray5 * 256;
				Gray5 = pixLess[pos];
				Gray4 = pixGreater[pos];
				/* if (Gray7 > Gray8) Swap(Gray7, Gray8);*/
				pos = Gray7 + Gray8 * 256;
				Gray8 = pixLess[pos];
				Gray7 = pixGreater[pos];
				/*    if (Gray0 > Gray1) Swap(Gray0, Gray1);*/
				pos = Gray0 + Gray1 * 256;
				Gray1 = pixLess[pos];
				Gray0 = pixGreater[pos];
				/* if (Gray3 > Gray4) Swap(Gray3, Gray4);*/
				pos = Gray3 + Gray4 * 256;
				Gray4 = pixLess[pos];
				Gray3 = pixGreater[pos];
				/*    if (Gray6 > Gray7) Swap(Gray6, Gray7);*/
				pos = Gray6 + Gray7 * 256;
				Gray7 = pixLess[pos];
				Gray6 = pixGreater[pos];
				/* if (Gray1 > Gray2) Swap(Gray1, Gray2);*/
				pos = Gray1 + Gray2 * 256;
				Gray2 = pixLess[pos];
				Gray1 = pixGreater[pos];
				/* if (Gray4 > Gray5) Swap(Gray4, Gray5);*/
				pos = Gray4 + Gray5 * 256;
				Gray5 = pixLess[pos];
				Gray4 = pixGreater[pos];
				/* if (Gray7 > Gray8) Swap(Gray7, Gray8);*/
				pos = Gray7 + Gray8 * 256;
				Gray8 = pixLess[pos];
				Gray7 = pixGreater[pos];
				/* if (Gray0 > Gray3) Swap(Gray0, Gray3);*/
				pos = Gray0 + Gray3 * 256;
				Gray3 = pixLess[pos];
				Gray0 = pixGreater[pos];
				/* if (Gray5 > Gray8) Swap(Gray5, Gray8);*/
				pos = Gray5 + Gray8 * 256;
				Gray8 = pixLess[pos];
				Gray5 = pixGreater[pos];
				/*    if (Gray4 > Gray7) Swap(Gray4, Gray7);*/
				pos = Gray4 + Gray7 * 256;
				Gray7 = pixLess[pos];
				Gray4 = pixGreater[pos];
				/* if (Gray3 > Gray6) Swap(Gray3, Gray6);*/
				pos = Gray3 + Gray6 * 256;
				Gray6 = pixLess[pos];
				Gray3 = pixGreater[pos];
				/* if (Gray1 > Gray4) Swap(Gray1, Gray4);*/
				pos = Gray1 + Gray4 * 256;
				Gray4 = pixLess[pos];
				Gray1 = pixGreater[pos];
				/*    if (Gray2 > Gray5) Swap(Gray2, Gray5);*/
				pos = Gray2 + Gray5 * 256;
				Gray5 = pixLess[pos];
				Gray2 = pixGreater[pos];
				/*    if (Gray4 > Gray7) Swap(Gray4, Gray7);*/
				pos = Gray4 + Gray7 * 256;
				Gray7 = pixLess[pos];
				Gray4 = pixGreater[pos];
				/*    if (Gray4 > Gray2) Swap(Gray4, Gray2);*/
				pos = Gray4 + Gray2 * 256;
				Gray2 = pixLess[pos];
				Gray4 = pixGreater[pos];
				/* if (Gray6 > Gray4) Swap(Gray6, Gray4);*/
				pos = Gray6 + Gray4 * 256;
				Gray4 = pixLess[pos];
				Gray6 = pixGreater[pos];
				/*    if (Gray4 > Gray2) Swap(Gray4, Gray2); */
				pos = Gray4 + Gray2 * 256;
				Gray2 = pixLess[pos];
				Gray4 = pixGreater[pos];

				LinePD[1] = Gray4;
				LinePD++;
			}
		}
		return Ret;
	}
	else
	{
		TMatrix *Blue = NULL, *Green = NULL, *Red = NULL, *Alpha = NULL;     //    由于C变量如果不初始化，其值是随机值，可能会导致释放时的错误。
		IS_RET Ret = SplitRGBA(Src, &Blue, &Green, &Red, &Alpha);
		if (Ret != IS_RET_OK) goto Done24;
#pragma omp parallel num_threads(3)
		{
#pragma omp sections
   {
#pragma omp section
	{
		Ret = Fastest33MedianBlur(Blue, Blue);
	}
#pragma omp section
	{
		Ret = Fastest33MedianBlur(Green, Green);
	}
#pragma omp section
	{
		Ret = Fastest33MedianBlur(Red, Red);
	}

   }
		}
		Ret = CombineRGBA(Dest, Blue, Green, Red, Alpha);
	Done24:
		IS_FreeMatrix(&Blue);
		IS_FreeMatrix(&Green);
		IS_FreeMatrix(&Red);
		IS_FreeMatrix(&Alpha);
		return Ret;
	}

	return Ret;
}

　　关于交换法短值快速排序的参考资料见：https://github.com/afniHQ/AFNI/blob/ab8ca253b784ae71401927df88da2bc6e16d07c1/src/cs_qsort_small.h