PKU ACM 1009 Edge Detection 边缘提取算法

最新推荐文章于 2019-07-07 01:10:55 发布

huxin2007

最新推荐文章于 2019-07-07 01:10:55 发布

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分类专栏： ACM 文章标签： null 算法 struct 存储

本文链接：https://blog.youkuaiyun.com/huxin2007/article/details/6816979

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该博客介绍了如何使用边缘提取算法处理输入图像，通过计算当前像素与周围8个像素的差值来确定输出图像。算法核心在于只在输入图像的像素变化点及其相邻点处更新输出图像。内容包括算法思路和源代码，图像数据以游程编码存储。

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题目链接：Edge Detection 边缘提取算法

题目描述：

对输入图像进行边缘提取，算法是分别计算当前像素和周围8个像素之间的差，最大值就是提取后的像素值。

输入图像和输出图像都按照游程编码存储。

主要思路：

不能计算每个像素的值，会导致TL。其实，只在以下几种情况下，输出像素与前一个像素的值不同（变化点）

1. 输入图像中某个点对比前一个点发生了变化，那么它周围的 8 个点可能是输出图像中的变化点

2. 输入图像中某一行的像素值变化了，那么当前行的左右两个端点可能是输出图像中的变化点

源代码：

#include <iostream>
using namespace std;

struct Point
{
	int pos;
	int val;
	Point* pNext;
};

struct RLE
{
	int val;
	int len;
};

RLE iRLE[10000];
Point* pFirst;
int width;
int iRLElen;
int sum;

int GetVal(int pos)
{
	int curpos = 0;
	if((pos >= 0) && (pos < iRLE[0].len))
		return iRLE[0].val;

	for(int i = 1; i < iRLElen; i++)
	{
		curpos = curpos + iRLE[i-1].len;
		if((pos >= curpos) && (pos < curpos + iRLE[i].len))
			return iRLE[i].val;
	}
	return 0;
}

void GetBorderPoint(int pos)
{
	Point* pb = pFirst;
	Point* ppre = pFirst;
	while(pb != NULL)
	{
		if(pb->pos == pos)
			return;
		if(pb->pos > pos)
			break;
		ppre = pb;
		pb = pb->pNext;
	}


	int surround[8] = {0};
	int max = 0;
	int val = GetVal(pos);
	if(pos >= width)
		surround[0] = abs(GetVal(pos - width) - val);
	if(pos < sum - width)
		surround[1] = abs(GetVal(pos + width) - val);
	if(pos % width > 0)
		surround[2] = abs(GetVal(pos - 1) - val);
	if(pos % width < width - 1)
		surround[3] = abs(GetVal(pos + 1) - val);

	if((pos >= width) && (pos % width > 0))
		surround[4] = abs(GetVal(pos - width - 1) - val);
	if((pos >= width) && (pos % width < width - 1))
		surround[5] = abs(GetVal(pos - width + 1) - val);
	if((pos < sum - width) && (pos % width > 0))
		surround[6] = abs(GetVal(pos + width - 1) - val);
	if((pos < sum - width) && (pos % width < width - 1))
		surround[7] = abs(GetVal(pos + width + 1) - val);

	for(int i = 0; i < 8; i++)
	{
		if(surround[i] > max)
			max = surround[i];
	}

	if(pFirst == NULL)
	{
		pFirst = new Point;
		pFirst->pos = pos;
		pFirst->val = max;
		pFirst->pNext = NULL;
	}
	else
	{
		Point* newpoint = new Point;
		newpoint->pos = pos;
		newpoint->val = max;
		newpoint->pNext  = pb;
		ppre->pNext = newpoint;
	}
}

void GetBorder(int pos)
{
	GetBorderPoint(pos);
	if(pos >= width)
		GetBorderPoint(pos - width);
	if(pos < sum - width)
		GetBorderPoint(pos + width);
	if(pos % width > 0)
		GetBorderPoint(pos - 1);
	if(pos % width < width - 1)
		GetBorderPoint(pos + 1);

	if((pos >= width) && (pos % width > 0))
		GetBorderPoint(pos - width - 1);
	if((pos >= width) && (pos % width < width - 1))
		GetBorderPoint(pos - width + 1);
	if((pos < sum - width) && (pos % width > 0))
		GetBorderPoint(pos + width - 1);
	if((pos < sum - width) && (pos % width < width - 1))
		GetBorderPoint(pos + width + 1);
	
	GetBorderPoint((pos / width) * width);
	GetBorderPoint((pos / width + 1) * width - 1);
}

void PrintResult()
{
	cout << width << endl;
	Point* pb = pFirst;
	Point* preb = pFirst;
	int prepos = 0;
	int preval = pFirst->val;
	while(pb != NULL)
	{
		if(pb->val != preval)
		{
			cout << preval << " " << pb->pos - prepos << endl;
			preval = pb->val;
			prepos = pb->pos;
		}
		preb = pb;
		pb = pb->pNext;
		delete preb;
	}
	cout << preval << " " << sum - prepos << endl;
	cout << "0 0" << endl;
}

int main()
{
	while(true)
	{
		cin >> width;
		if(!width)	break;

		iRLElen = 0;
		sum = 0;
		pFirst = NULL;
		memset(iRLE, 0, sizeof(iRLE));

		while(true)
		{
			cin >> iRLE[iRLElen].val >> iRLE[iRLElen].len;
			sum = iRLE[iRLElen].len + sum;
			if(iRLE[iRLElen].len == 0)
				break;
			iRLElen++;
		}

		int curpos = 0;
		GetBorder(curpos);
		GetBorder(curpos + iRLE[0].len - 1);

		for(int i = 1; i < iRLElen; i++)
		{
			curpos = curpos + iRLE[i-1].len;
			GetBorder(curpos);
			GetBorder(curpos + iRLE[i].len - 1);
		}

		PrintResult();
	}

	cout << "0" << endl;
	return 0;
}