并行计算 Blog 01 —— SLIC代码切分

并行计算 Blog 01

---

SLIC 代码切分

---

1. 函数头

#include 
#include 
#include 
#include 
#include 
#include "SLIC.h"
#include 

typedef chrono::high_resolution_clock Clock;

// For superpixels
const int dx4[4] = {-1,  0,  1,  0};
const int dy4[4] = { 0, -1,  0,  1};
//const int dx8[8] = {-1, -1,  0,  1, 1, 1, 0, -1};
//const int dy8[8] = { 0, -1, -1, -1, 0, 1, 1,  1};

// For supervoxels
const int dx10[10] = {-1,  0,  1,  0, -1,  1,  1, -1,  0, 0};
const int dy10[10] = { 0, -1,  0,  1, -1, -1,  1,  1,  0, 0};
const int dz10[10] = { 0,  0,  0,  0,  0,  0,  0,  0, -1, 1};

• chono.h
  系统计时的头文件，计算效率
  https://blog.csdn.net/fengbingchun/article/details/73302364

• dx4[], dy4[] superpixel 超像素的方向辅助数组

• dx10[], dy10[] supervoxels 超体素（三维坐标的方向数组）

---

2. SLIC 的类函数

2.1 构造函数和析构函数

这一部分注意 初始化的值，同时搞清楚使用的数据结构

主要是 L, A, B 这三个维度的值

一维作用：

二维作用：

// Construction/Destruction
SLIC::SLIC()
{
	m_lvec = NULL;
	m_avec = NULL;
	m_bvec = NULL;

	m_lvecvec = NULL;
	m_avecvec = NULL;
	m_bvecvec = NULL;
}

SLIC::~SLIC()
{
	if(m_lvec) delete [] m_lvec;
	if(m_avec) delete [] m_avec;
	if(m_bvec) delete [] m_bvec;

	if(m_lvecvec)
	{
		for( int d = 0; d < m_depth; d++ ) delete [] m_lvecvec[d];
		delete [] m_lvecvec;
	}
	if(m_avecvec)
	{
		for( int d = 0; d < m_depth; d++ ) delete [] m_avecvec[d];
		delete [] m_avecvec;
	}
	if(m_bvecvec)
	{
		for( int d = 0; d < m_depth; d++ ) delete [] m_bvecvec[d];
		delete [] m_bvecvec;
	}
}

2.2 功能函数 RGB2XYZ 数据格式的转变

参数转换的参数依据：？

*加速：pow(double, double) 手写优化？

void SLIC::RGB2XYZ(
	const int&		sR,
	const int&		sG,
	const int&		sB,
	double&			X,
	double&			Y,
	double&			Z)
{
	double R = sR/255.0;
	double G = sG/255.0;
	double B = sB/255.0;

	double r, g, b;

	if(R <= 0.04045)	r = R/12.92;
	else				r = pow((R+0.055)/1.055,2.4);
	if(G <= 0.04045)	g = G/12.92;
	else				g = pow((G+0.055)/1.055,2.4);
	if(B <= 0.04045)	b = B/12.92;
	else				b = pow((B+0.055)/1.055,2.4);

	X = r*0.4124564 + g*0.3575761 + b*0.1804375;
	Y = r*0.2126729 + g*0.7151522 + b*0.0721750;
	Z = r*0.0193339 + g*0.1191920 + b*0.9503041;
}

2.3 转换函数：RGB2LAB

*加速点：依旧是浮点数的快速乘法

//	RGB2LAB
void SLIC::RGB2LAB(
	const int& sR, const int& sG, const int& sB, 
	double& lval, double& aval, double& bval)
{

	// sRGB to XYZ conversion
	double X, Y, Z;
	RGB2XYZ(sR, sG, sB, X, Y, Z);

	// XYZ to LAB conversion
	double epsilon = 0.008856;	//actual CIE standard
	double kappa   = 903.3;		//actual CIE standard

	double Xr = 0.950456;	//reference white
	double Yr = 1.0;		//reference white
	double Zr = 1.088754;	//reference white

	double xr = X/Xr;
	double yr = Y/Yr;
	double zr = Z/Zr;

	double fx, fy, fz;
	if(xr > epsilon)	fx = pow(xr, 1.0/3.0);
	else				fx = (kappa*xr + 16.0)/116.0;
	if(yr > epsilon)	fy = pow(yr, 1.0/3.0);
	else				fy = (kappa*yr + 16.0)/116.0;
	if(zr > epsilon)	fz = pow(zr, 1.0/3.0);
	else				fz = (kappa*zr + 16.0)/116.0;

	lval = 116.0*fy-16.0;
	aval = 500.0*(fx-fy);
	bval = 200.0*(fy-fz);
}

2.4 功能函数：DoRGBtoLABConversion

全图的 RGB to LAB 的格式转换

rgb 24位， r 8bit g 8bit b 8bit 已经是位运算了

*优化：new 分配空间可不可以优化

** 优化： RGB 拆成三个线程跑，ubuff 是const，只进行数据读

//	DoRGBtoLABConversion
//	For whole image: overlaoded floating point version
void SLIC::DoRGBtoLABConversion(
	const unsigned int*&		ubuff,
	double*&					lvec,
	double*&					avec,
	double*&					bvec)
{
	int sz = m_width*m_height;
	lvec = new double[sz];
	avec = new double[sz];
	bvec = new double[sz];

	for( int j = 0; j < sz; j++ )
	{
		int r = (ubuff[j] >> 16) & 0xFF;
		int g = (ubuff[j] >>  8) & 0xFF;
		int b = (ubuff[j]      ) & 0xFF;

		RGB2LAB( r, g, b, lvec[j], avec[j], bvec[j] );
	}
}

2.5 核心功能函数：DetectLabEdges

全图的扫描计算每一个点的梯度（除了最外部的一圈像素）

对应论文中 ： G(x, y) = ||I(x+1, y) - I(x-1, y)|| + ||I(x, y+1) - I(x, y-1)||

//	DetectLabEdges
void SLIC::DetectLabEdges(
	const double*				lvec,
	const double*				avec,
	const double*				bvec,
	const int&					width,
	const int&					height,
	vector<double>&				edges)
{
	int sz = width*height;

	edges.resize(sz,0);
	for( int j = 1; j < height-1; j++ )
	{
		for( int k = 1; k < width-1; k++ )
		{
			int i = j*width+k;

			double dx = (lvec[i-1]-lvec[i+1])*(lvec[i-1]-lvec[i+1]) +
						(avec[i-1]-avec[i+1])*(avec[i-1]-avec[i+1]) +
						(bvec[i-1]-bvec[i+1])*(bvec[i-1]-bvec[i+1]);

			double dy = (lvec[i-width]-lvec[i+width])*(lvec[i-width]-lvec[i+width]) +
						(avec[i-width]-avec[i+width])*(avec[i-width]-avec[i+width]) +
						(bvec[i-width]-bvec[i+width])*(bvec[i-width]-bvec[i+width]);

			//edges[i] = (sqrt(dx) + sqrt(dy));
			edges[i] = (dx + dy);
		}
	}
}

2.6 核心功能函数：PerturbSeeds

功能：枚举每个当前的 超像素点，从 3 * 3 的范围中找到 G 值 (edges) 最小的迁移过去
G 值在 2.5 中计算得到，图像不变则G值不变，即在计算过程中 G值是固定的。

//	PerturbSeeds
void SLIC::PerturbSeeds(
	vector<double>&				kseedsl,
	vector<double>&				kseedsa,
	vector<double>&				kseedsb,
	vector<double>&				kseedsx,
	vector<double>&				kseedsy,
	const vector<double>&		edges)
{
	const int dx8[8] = {-1, -1,  0,  1, 1, 1, 0, -1};
	const int dy8[8] = { 0, -1, -1, -1, 0, 1, 1,  1};
	
	int numseeds = kseedsl.size();

	for( int n = 0; n < numseeds; n++ )
	{
		int ox = kseedsx[n];	//original x
		int oy = kseedsy[n];	//original y
		int oind = oy*m_width + ox;	// ind  --> index

		int storeind = oind;
		for( int i = 0; i < 8; i++ )
		{
			int nx = ox+dx8[i];	//new x
			int ny = oy+dy8[i];	//new y

			if( nx >= 0 && nx < m_width && ny >= 0 && ny < m_height)
			{
				int nind = ny*m_width + nx;
				if( edges[nind] < edges[storeind])
				{
					storeind = nind;
				}
			}
		}
		if(storeind != oind)
		{
			kseedsx[n] = storeind % m_width;
			kseedsy[n] = storeind / m_width;
			kseedsl[n] = m_lvec[storeind];
			kseedsa[n] = m_avec[storeind];
			kseedsb[n] = m_bvec[storeind];
		}
	}
}

2.7 核心初始化函数：GetLABXYSeeds_ForGivenK、

最初的 K 个超像素是如何选择的？
就是在全图上直接画格子找出来，平均地去找。

//	GetLABXYSeeds_ForGivenK
// The k seed values are taken as uniform spatial pixel samples.
void SLIC::GetLABXYSeeds_ForGivenK(
	vector<double>&				kseedsl,
	vector<double>&				kseedsa,
	vector<double>&				kseedsb,
	vector<double>&				kseedsx,
	vector<double>&				kseedsy,
	const int&					K,
	const bool&					perturbseeds,
	const vector<double>&		edgemag)
{
	int sz = m_width*m_height;
	double step = sqrt(double(sz)/double(K));
	int T = step;
	int xoff = step/2;
	int yoff = step/2;
	
	int n(0);int r(0);
	for( int y = 0; y < m_height; y++ )
	{
		int Y = y*step + yoff;
		if( Y > m_height-1 ) break;

		for( int x = 0; x < m_width; x++ )
		{
			//int X = x*step + xoff;//square grid
			int X = x*step + (xoff<<(r&0x1));//hex grid
			if(X > m_width-1) break;

			int i = Y*m_width + X;

			//_ASSERT(n < K);
			
			//kseedsl[n] = m_lvec[i];
			//kseedsa[n] = m_avec[i];
			//kseedsb[n] = m_bvec[i];
			//kseedsx[n] = X;
			//kseedsy[n] = Y;
			kseedsl.push_back(m_lvec[i]);
			kseedsa.push_back(m_avec[i]);
			kseedsb.push_back(m_bvec[i]);
			kseedsx.push_back(X);
			kseedsy.push_back(Y);
			n++;
		}
		r++;
	}

	if(perturbseeds)
	{
		PerturbSeeds(kseedsl, kseedsa, kseedsb, kseedsx, kseedsy, edgemag);
	}
}

2.8 核心函数：PerformSuperpixelSegmentation_VariableSandM

功能：？

//===========================================================================
///	PerformSuperpixelSegmentation_VariableSandM
///
///	Magic SLIC - no parameters
///
///	Performs k mean segmentation. It is fast because it looks locally, not
/// over the entire image.
/// This function picks the maximum value of color distance as compact factor
/// M and maximum pixel distance as grid step size S from each cluster (13 April 2011).
/// So no need to input a constant value of M and S. There are two clear
/// advantages:
///
/// [1] The algorithm now better handles both textured and non-textured regions
/// [2] There is not need to set any parameters!!!
///
/// SLICO (or SLIC Zero) dynamically varies only the compactness factor S,
/// not the step size S.
//===========================================================================

void SLIC::PerformSuperpixelSegmentation_VariableSandM(
	vector<double>&				kseedsl,
	vector<double>&				kseedsa,
	vector<double>&				kseedsb,
	vector<double>&				kseedsx,
	vector<double>&				kseedsy,
	int*						klabels,
	const int&					STEP,
	const int&					NUMITR)
{
	int sz = m_width*m_height;
	const int numk = kseedsl.size();
	//double cumerr(99999.9);
	int numitr(0);

	//----------------
	int offset = STEP;
	if(STEP < 10) offset = STEP*1.5;
	//----------------

	vector<double> sigmal(numk, 0);
	vector<double> sigmaa(numk, 0);
	vector<double> sigmab(numk, 0);
	vector<double> sigmax(numk, 0);
	vector<double> sigmay(numk, 0);
	vector<int> clustersize(numk, 0);
	vector<double> inv(numk, 0);	//to store 1/clustersize[k] values
	vector<double> distxy(sz, DBL_MAX);
	vector<double> distlab(sz, DBL_MAX);
	vector<double> distvec(sz, DBL_MAX);
	vector<double> maxlab(numk, 10*10);	//THIS IS THE VARIABLE VALUE OF M, just start with 10
	vector<double> maxxy(numk, STEP*STEP);	//THIS IS THE VARIABLE VALUE OF M, just start with 10

	double invxywt = 1.0/(STEP*STEP);	//NOTE: this is different from how usual SLIC/LKM works

	while( numitr < NUMITR )
	{
		//------
		//cumerr = 0;
		numitr++;
		//------

		distvec.assign(sz, DBL_MAX);
		for( int n = 0; n < numk; n++ )
		{
			int y1 = max(0,			(int)(kseedsy[n]-offset));
			int y2 = min(m_height,	(int)(kseedsy[n]+offset));
			int x1 = max(0,			(int)(kseedsx[n]-offset));
			int x2 = min(m_width,	(int)(kseedsx[n]+offset));

			for( int y = y1; y < y2; y++ )
			{
				for( int x = x1; x < x2; x++ )
				{
					int i = y*m_width + x;
					//_ASSERT( y < m_height && x < m_width && y >= 0 && x >= 0 );

					double l = m_lvec[i];
					double a = m_avec[i];
					double b = m_bvec[i];

					distlab[i] =	(l - kseedsl[n])*(l - kseedsl[n]) +
									(a - kseedsa[n])*(a - kseedsa[n]) +
									(b - kseedsb[n])*(b - kseedsb[n]);

					distxy[i] =		(x - kseedsx[n])*(x - kseedsx[n]) +
									(y - kseedsy[n])*(y - kseedsy[n]);

					//------------------------------------------------------------------------
					double dist = distlab[i]/maxlab[n] + distxy[i]*invxywt;	//only varying m, prettier superpixels
					//double dist = distlab[i]/maxlab[n] + distxy[i]/maxxy[n];//varying both m and S
					//------------------------------------------------------------------------
					
					if( dist < distvec[i] )
					{
						distvec[i] = dist;
						klabels[i]  = n;
					}
				}
			}
		}
		//-----------------------------------------------------------------
		// Assign the max color distance for a cluster
		//-----------------------------------------------------------------
		if(0 == numitr)
		{
			maxlab.assign(numk,1);
			maxxy.assign(numk,1);
		}
		{for( int i = 0; i < sz; i++ )
		{
			if(maxlab[klabels[i]] < distlab[i]) maxlab[klabels[i]] = distlab[i];
			if(maxxy[klabels[i]] < distxy[i]) maxxy[klabels[i]] = distxy[i];
		}}
		//-----------------------------------------------------------------
		// Recalculate the centroid and store in the seed values
		//-----------------------------------------------------------------
		sigmal.assign(numk, 0);
		sigmaa.assign(numk, 0);
		sigmab.assign(numk, 0);
		sigmax.assign(numk, 0);
		sigmay.assign(numk, 0);
		clustersize.assign(numk, 0);

		for( int j = 0; j < sz; j++ )
		{
			int temp = klabels[j];
			//_ASSERT(klabels[j] >= 0);
			sigmal[klabels[j]] += m_lvec[j];
			sigmaa[klabels[j]] += m_avec[j];
			sigmab[klabels[j]] += m_bvec[j];
			sigmax[klabels[j]] += (j%m_width);
			sigmay[klabels[j]] += (j/m_width);

			clustersize[klabels[j]]++;
		}

		{for( int k = 0; k < numk; k++ )
		{
			//_ASSERT(clustersize[k] > 0);
			if( clustersize[k] <= 0 ) clustersize[k] = 1;
			inv[k] = 1.0/double(clustersize[k]);//computing inverse now to multiply, than divide later
		}}
		
		{for( int k = 0; k < numk; k++ )
		{
			kseedsl[k] = sigmal[k]*inv[k];
			kseedsa[k] = sigmaa[k]*inv[k];
			kseedsb[k] = sigmab[k]*inv[k];
			kseedsx[k] = sigmax[k]*inv[k];
			kseedsy[k] = sigmay[k]*inv[k];
		}}
	}
}

2.9 辅助函数：SaveSuperpixelLabels2PPM

将文件存为PPM格式，方便校验
非功能重点，无需修改

// 	SaveSuperpixelLabels2PGM
//	Save labels to PGM in raster scan order.
void SLIC::SaveSuperpixelLabels2PPM(
	char*                           filename, 
	int *                           labels, 
	const int                       width, 
	const int                       height)
{
    FILE* fp;
    char header[20];
 
    fp = fopen(filename, "wb");
 
    // write the PPM header info, such as type, width, height and maximum
    fprintf(fp,"P6\n%d %d\n255\n", width, height);
 
    // write the RGB data
    unsigned char *rgb = new unsigned char [ (width)*(height)*3 ];
    int k = 0;
	unsigned char c = 0;
    for ( int i = 0; i < (height); i++ ) {
        for ( int j = 0; j < (width); j++ ) {
			c = (unsigned char)(labels[k]);
            rgb[i*(width)*3 + j*3 + 2] = labels[k] >> 16 & 0xff;  // r
            rgb[i*(width)*3 + j*3 + 1] = labels[k] >> 8  & 0xff;  // g
            rgb[i*(width)*3 + j*3 + 0] = labels[k]       & 0xff;  // b

			// rgb[i*(width) + j + 0] = c;
            k++;
        }
    }
    fwrite(rgb, width*height*3, 1, fp);

    delete [] rgb;
 
    fclose(fp);
}

2.10 核心函数：EnforceLabelConnectivity

功能：？

//	EnforceLabelConnectivity
//		1. finding an adjacent label for each new component at the start
//		2. if a certain component is too small, assigning the previously found
//		    adjacent label to this component, and not incrementing the label.

void SLIC::EnforceLabelConnectivity(
	const int*					labels,
	//input labels that need to be corrected to remove stray labels
	const int&					width,
	const int&					height,
	int*						nlabels,	//new labels
	int&						numlabels,	
	//the number of labels changes in the end if segments are removed
	const int&					K) 
	//the number of superpixels desired by the user
{
//	const int dx8[8] = {-1, -1,  0,  1, 1, 1, 0, -1};
//	const int dy8[8] = { 0, -1, -1, -1, 0, 1, 1,  1};

	const int dx4[4] = {-1,  0,  1,  0};
	const int dy4[4] = { 0, -1,  0,  1};

	const int sz = width*height;
	const int SUPSZ = sz/K;
	//nlabels.resize(sz, -1);
	for( int i = 0; i < sz; i++ ) nlabels[i] = -1;
	int label(0);
	int* xvec = new int[sz];
	int* yvec = new int[sz];
	int oindex(0);
	int adjlabel(0);//adjacent label
	for( int j = 0; j < height; j++ )
	{
		for( int k = 0; k < width; k++ )
		{
			if( 0 > nlabels[oindex] )
			{
				nlabels[oindex] = label;
				-
				// Start a new segment
				xvec[0] = k;
				yvec[0] = j;
	
				// Quickly find an adjacent label for use later if needed
				{for( int n = 0; n < 4; n++ )
				{
					int x = xvec[0] + dx4[n];
					int y = yvec[0] + dy4[n];
					if( (x >= 0 && x < width) && (y >= 0 && y < height) )
					{
						int nindex = y*width + x;
						if(nlabels[nindex] >= 0) adjlabel = nlabels[nindex];
					}
				}}

				int count(1);
				for( int c = 0; c < count; c++ )
				{
					for( int n = 0; n < 4; n++ )
					{
						int x = xvec[c] + dx4[n];
						int y = yvec[c] + dy4[n];

						if( (x >= 0 && x < width) && (y >= 0 && y < height) )
						{
							int nindex = y*width + x;

							if( 0 > nlabels[nindex] && labels[oindex] == labels[nindex] )
							{
								xvec[count] = x;
								yvec[count] = y;
								nlabels[nindex] = label;
								count++;
							}
						}
					}
				}
				
				// If segment size is less then a limit, assign an
				// adjacent label found before, and decrement label count.
				if(count <= SUPSZ >> 2)
				{
					for( int c = 0; c < count; c++ )
					{
						int ind = yvec[c]*width+xvec[c];
						nlabels[ind] = adjlabel;
					}
					label--;
				}
				label++;
			}
			oindex++;
		}
	}
	numlabels = label;

	if(xvec) delete [] xvec;
	if(yvec) delete [] yvec;
}

2.11 核心函数: PerformSLICO_ForGivenK

功能:

//	PerformSLICO_ForGivenK
// Zero parameter SLIC algorithm for a given number K of superpixels.
void SLIC::PerformSLICO_ForGivenK(
	const unsigned int*			ubuff,
	const int					width,
	const int					height,
	int*						klabels,
	int&						numlabels,
	const int&					K,//required number of superpixels
	const double&				m)//weight given to spatial distance
{
	vector<double> kseedsl(0);
	vector<double> kseedsa(0);
	vector<double> kseedsb(0);
	vector<double> kseedsx(0);
	vector<double> kseedsy(0);

	//--------------------------------------------------
	m_width  = width;
	m_height = height;
	int sz = m_width*m_height;
	//--------------------------------------------------
	//if(0 == klabels) klabels = new int[sz];
	for( int s = 0; s < sz; s++ ) klabels[s] = -1;
	//--------------------------------------------------
	if(1)//LAB
	{
		DoRGBtoLABConversion(ubuff, m_lvec, m_avec, m_bvec);
	}
	else//RGB
	{
		m_lvec = new double[sz]; m_avec = new double[sz]; m_bvec = new double[sz];
		for( int i = 0; i < sz; i++ )
		{
			m_lvec[i] = ubuff[i] >> 16 & 0xff;
			m_avec[i] = ubuff[i] >>  8 & 0xff;
			m_bvec[i] = ubuff[i]       & 0xff;
		}
	}
	//--------------------------------------------------

	bool perturbseeds(true);
	vector<double> edgemag(0);
	if(perturbseeds) DetectLabEdges(m_lvec, m_avec, m_bvec, m_width, m_height, edgemag);
	GetLABXYSeeds_ForGivenK(kseedsl, kseedsa, kseedsb, kseedsx, kseedsy, K, perturbseeds, edgemag);

	int STEP = sqrt(double(sz)/double(K)) + 2.0;//adding a small value in the even the STEP size is too small.
	PerformSuperpixelSegmentation_VariableSandM(kseedsl,kseedsa,kseedsb,kseedsx,kseedsy,klabels,STEP,10);
	numlabels = kseedsl.size();

	int* nlabels = new int[sz];
	EnforceLabelConnectivity(klabels, m_width, m_height, nlabels, numlabels, K);
	{for(int i = 0; i < sz; i++ ) klabels[i] = nlabels[i];}
	if(nlabels) delete [] nlabels;
}

以上为 SLIC 的算法主体

---

3.1 辅助函数: LoadPPM

非重点

// Load PPM file
void LoadPPM(char* filename, unsigned int** data, int* width, int* height)
{
    char header[1024];
    FILE* fp = NULL;
    int line = 0;
 
    fp = fopen(filename, "rb");
 
    // read the image type, such as: P6
    // skip the comment lines
    while (line < 2) {    
        fgets(header, 1024, fp);
        if (header[0] != '#') {
            ++line;
        }
    }
    // read width and height
    sscanf(header,"%d %d\n", width, height);
 
    // read the maximum of pixels
    fgets(header, 20, fp);
 
    // get rgb data
    unsigned char *rgb = new unsigned char [ (*width)*(*height)*3 ];
    fread(rgb, (*width)*(*height)*3, 1, fp);

    *data = new unsigned int [ (*width)*(*height)*4 ];
    int k = 0;
    for ( int i = 0; i < (*height); i++ ) {
        for ( int j = 0; j < (*width); j++ ) {
            unsigned char *p = rgb + i*(*width)*3 + j*3;
                                      // a ( skipped )
            (*data)[k]  = p[2] << 16; // r
            (*data)[k] |= p[1] << 8;  // g
            (*data)[k] |= p[0];       // b
            k++;
        }
    }

    // ofc, later, you'll have to cleanup
    delete [] rgb;
 
    fclose(fp);
}

2.11-2 辅助函数：CheckLabelswithPPM

非重点

// Load PPM file
int CheckLabelswithPPM(char* filename, int* labels, int width, int height)
{
    char header[1024];
    FILE* fp = NULL;
    int line = 0, ground = 0;
 
    fp = fopen(filename, "rb");
 
    // read the image type, such as: P6
    // skip the comment lines
    while (line < 2) {    
        fgets(header, 1024, fp);
        if (header[0] != '#') {
            ++line;
        }
    }
    // read width and height
	int w(0);
	int h(0);
    sscanf(header,"%d %d\n", &w, &h);
	if (w != width || h != height) return -1;
 
    // read the maximum of pixels
    fgets(header, 20, fp);
 
    // get rgb data
    unsigned char *rgb = new unsigned char [ (w)*(h)*3 ];
    fread(rgb, (w)*(h)*3, 1, fp);

    int num = 0, k = 0;
    for ( int i = 0; i < (h); i++ ) {
        for ( int j = 0; j < (w); j++ ) {
            unsigned char *p = rgb + i*(w)*3 + j*3;
                                  // a ( skipped )
            ground  = p[2] << 16; // r
            ground |= p[1] << 8;  // g
            ground |= p[0];       // b
            
			if (ground != labels[k])
				num++;

			k++;
        }
    }

    // ofc, later, you'll have to cleanup
    delete [] rgb;
    fclose(fp);
	return num;
}

---

主函数

int main (int argc, char **argv)
{
	unsigned int* img = NULL;
	int width(0);
	int height(0);

	LoadPPM((char *)"input_image.ppm", &img, &width, &height);
	if (width == 0 || height == 0) return -1;

	int sz = width*height;
	int* labels = new int[sz];
	int numlabels(0);
	SLIC slic;
	int m_spcount;
	double m_compactness;
	m_spcount = 200;
	m_compactness = 10.0;
    auto startTime = Clock::now();
	slic.PerformSLICO_ForGivenK(img, width, height, labels, numlabels, m_spcount, m_compactness);//for a given number K of superpixels
    auto endTime = Clock::now();
    auto compTime = chrono::duration_cast<chrono::microseconds>(endTime - startTime);
    cout <<  "Computing time=" << compTime.count()/1000 << " ms" << endl;

	int num = CheckLabelswithPPM((char *)"check.ppm", labels, width, height);
	if (num < 0) {
		cout <<  "The result for labels is different from output_labels.ppm." << endl;
	} else {
		cout <<  "There are " << num << " points' labels are different from original file." << endl;
	}
	
	slic.SaveSuperpixelLabels2PPM((char *)"output_labels.ppm", labels, width, height);
	if(labels) delete [] labels;
	
	if(img) delete [] img;

	return 0;
}