解題區/解題區 - Zerojudge

b448. 哈哈鏡

contents

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

Problem

進行圖片變形，效果類似哈哈鏡的作用。

對圖片水平中線進行座標 y' = sqrt(y) 變換，將靠近中線的像素盡可能地拉往中間，形成延伸的變形效果。

Sample Input

1
2
1 1
1 2 3

Sample Output

1
2
1 1
1 2 3

Solution

計算公式

  • 中線之上 (H/2) - pow(i-H/2, 2)/ (H/2)
  • 中線之下 pow(i-H/2, 2)/ (H/2) + H/2

分別套用後，逆轉換到原圖上，進行最近鄰居查找，。

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#include <bits/stdc++.h>
using namespace std;
class IMAGE {
public:
    struct Pixel {
        int r, g, b;
        Pixel(int x = 0, int y = 0, int z = 0):
        r(x), g(y), b(z) {}
        void read() {
            scanf("%d %d %d", &r, &g, &b);
        }
        Pixel operator-(const Pixel &x) const {
            return Pixel(r-x.r, g-x.g, b-x.b);
        }
        Pixel operator+(const Pixel &x) const {
            return Pixel(r+x.r, g+x.g, b+x.b);
        }
        Pixel operator*(const double x) const {
            return Pixel(r*x, g*x, b*x);
        }
        Pixel operator/(const double x) const {
            return Pixel(r/x, g/x, b/x);
        }
        bool operator==(const Pixel &x) const {
            return r == x.r && g == x.g && b == x.b;
        }
        void print() {
            printf("%d %d %d", r, g, b);
        }
        int sum() {
            return r + g + b;
        }
        int length() {
            return abs(r) + abs(g) + abs(b);
        }
        int dist(Pixel x) {
            return abs((r + g + b) - (x.r + x.g + x.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();
    }
    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' : ' ');
    }
    int isValid(int x, int y) {
        return x >= 0 && y >= 0 && x < H && y < W;
    }
    void distorting_mirror() {
        int rW = W, rH = H;
        double ch = H / 2.0;
        for (int i = 0; i < rH; i++) {
            double x, y;
            if (i < ch)
                x = ch - pow(i-ch, 2)/ch;
            else
                x = pow(i-ch, 2)/ch + ch;
            for (int j = 0; j < rW; j++) {
                y = j;
                int lx, rx, ly, ry;
                lx = floor(x), rx = ceil(x);
                ly = floor(y), ry = ceil(y);
                int px[] = {lx, lx, rx, rx};
                int py[] = {ly, ry, ly, ry};
                int c = -1;
                double mndist = 1e+30;
                for (int k = 0; k < 4; k++) {
                    if (!isValid(px[k], py[k]))
                        continue;
                    double d = (x-px[k])*(x-px[k])+(y-py[k])*(y-py[k]);
                    if (c == -1 || mndist > d)
                        c = k, mndist = d;
                }
                assert (c >= 0);
                tmp[i][j] = data[px[c]][py[c]];
            }
        }
        W = rW, H = rH;
        for (int i = 0; i < H; i++) {
            for (int j = 0; j < W; j++) {
                data[i][j] = tmp[i][j];
            }
        }
    }
} image;
int main() {
    image.read();
    image.distorting_mirror();
    image.print();
    return 0;	
}