解題區/解題區 - Zerojudge

b436. 圖片的梯度再進化

contents

  1. 1. Problem
  2. 2. Sample Input
  3. 3. Sample Output
  4. 4. Solution

Problem

可以參考 中央大學影像處理實驗室 課程 講義第八章 邊擷取

除了索貝爾運算 Sobel operator，還有如 Prewitt operator、Kirsch operator … 等，來進行邊擷取。

Sample Input

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2 2
0 0 0 255 255 255
255 255 255 255 255 255

Sample Output

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2 2
191 191 191 128 128 128
128 128 128 64 64 64

Solution

比較麻煩是在處理邊緣擴充，寫一個函數去特判延伸的 pixel 位置。

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#include <bits/stdc++.h> 
using namespace std;
class IMAGE {
public:
    struct Pixel {
        double r, g, b, a;
        Pixel(double x = 0, double y = 0, double z = 0, double w = 0):
            r(x), g(y), b(z), a(w) {}
        void read() {
            scanf("%lf %lf %lf", &r, &g, &b);
        }
        Pixel operator-(const Pixel &x) const {
        	return Pixel(r-x.r, g-x.g, b-x.b, a-x.a);
    	}
    	Pixel operator+(const Pixel &x) const {
        	return Pixel(r+x.r, g+x.g, b+x.b, a+x.a);
    	}
    	Pixel operator*(const double x) const {
        	return Pixel(r*x, g*x, b*x, a*x);
    	}
        Pixel operator/(const double x) const {
        	return Pixel(r/x, g/x, b/x, a/x);
    	}
    	void print() {
    		printf("%d %d %d", (int)round(r), (int)round(g), (int)round(b));
    	}
    };
    int W, H;
    static const int MAXN = 256;
    Pixel data[MAXN][MAXN], tmp[MAXN][MAXN];
    void read() {
        scanf("%d %d", &W, &H);
        for (int i = 0; i < H; i++)
            for (int j = 0; j < W; j++)
                data[i][j].read();
    }
    Pixel pabs(Pixel x) {
        return Pixel(fabs(x.r), fabs(x.g), fabs(x.b));
    }
    Pixel getPixel(int x, int y) {
        if (x >= 0 && y >= 0 && x < H && y < W)
            return data[x][y];
        if (y < 0)	return data[min(max(x, 0), H-1)][0];
        if (y >= W)	return data[min(max(x, 0), H-1)][W-1];
        if (x < 0)	return data[0][min(max(y, 0), W-1)];
        if (x >= H)	return data[H-1][min(max(y, 0), W-1)];
        return Pixel(0, 0, 0);
    }
    void border() {
        const int dx[] = {-1, -1, -1, 0, 0, 0, 1, 1, 1};
        const int dy[] = {-1, 0, 1, -1, 0, 1, -1, 0, 1};
        const int xw[] = {-1, 0, 1, -2, 0, 2, -1, 0, 1};
        const int yw[] = {-1, -2, -1, 0, 0, 0, 1, 2, 1};
        for (int i = 0; i < H; i++) {
            for (int j = 0; j < W; j++) {
                Pixel Dx(0, 0, 0), Dy(0, 0, 0);
                for (int k = 0; k < 9; k++) {
                    Dx = Dx + getPixel(i+dx[k], j+dy[k]) * xw[k];
                    Dy = Dy + getPixel(i+dx[k], j+dy[k]) * yw[k];
                }
                Dx = pabs(Dx), Dy = pabs(Dy);
                tmp[i][j] = (Dx + Dy)/8.0;
            }
        }
        for (int i = 0; i < H; i++)
            for (int j = 0; j < W; j++)
                data[i][j] = tmp[i][j];
    }
    void print() {
        printf("%d %d\n", W, H);
        for (int i = 0; i < H; i++)
            for (int j = 0; j < W; j++)
                data[i][j].print(), printf("%c", j == W-1 ? '\n' : ' ');
    }
} test;
int main() {
    test.read();
    test.border();
    test.print();
    return 0;
}