雙C插值C

Question

即時試圖處理雙cicubic圖像插值在c。所以我已經建立了這個小腳本。

1. 「resize_image」 -function：

void resize_image(PPMImage *source_image, PPMImage *destination_image, float scale) { 

     uint8_t sample[3]; 
     int y, x; 

     destination_image->x = (long)((float)(source_image->x)*scale); 
     destination_image->y = (long)((float)(source_image->y)*scale); 

     for (y = 0; y < destination_image->y; y++) { 

      float v = (float)y/(float)(destination_image->y - 1); 

      for (x = 0; x < destination_image->x; ++x) { 

       float u = (float)x/(float)(destination_image->x - 1); 
       sample_bicubic(source_image, u, v, sample); 

       destination_image->data[x+((destination_image->y)*y)].red = sample[0]; 
       destination_image->data[x+((destination_image->y)*y)].green = sample[1]; 
       destination_image->data[x+((destination_image->y)*y)].blue = sample[2]; 
      } 
     } 
    } 

2. 「sample_bicubic」 -function

void sample_bicubic(PPMImage *source_image, float u, float v, uint8_t sample[]) { 

     float x = (u * source_image->x)-0.5; 
     int xint = (int)x; 
     float xfract = x-floor(x); 

     float y = (v * source_image->y) - 0.5; 
     int yint = (int)y; 
     float yfract = y - floor(y); 

     int i; 

     uint8_t p00[3]; 
     uint8_t p10[3]; 
     uint8_t p20[3]; 
     uint8_t p30[3]; 

     uint8_t p01[3]; 
     uint8_t p11[3]; 
     uint8_t p21[3]; 
     uint8_t p31[3]; 

     uint8_t p02[3]; 
     uint8_t p12[3]; 
     uint8_t p22[3]; 
     uint8_t p32[3]; 

     uint8_t p03[3]; 
     uint8_t p13[3]; 
     uint8_t p23[3]; 
     uint8_t p33[3]; 

     // 1st row 
     get_pixel_clamped(source_image, xint - 1, yint - 1, p00); 
     get_pixel_clamped(source_image, xint + 0, yint - 1, p10); 
     get_pixel_clamped(source_image, xint + 1, yint - 1, p20); 
     get_pixel_clamped(source_image, xint + 2, yint - 1, p30); 

     // 2nd row 
     get_pixel_clamped(source_image, xint - 1, yint + 0, p01); 
     get_pixel_clamped(source_image, xint + 0, yint + 0, p11); 
     get_pixel_clamped(source_image, xint + 1, yint + 0, p21); 
     get_pixel_clamped(source_image, xint + 2, yint + 0, p31); 

     // 3rd row 
     get_pixel_clamped(source_image, xint - 1, yint + 1, p02); 
     get_pixel_clamped(source_image, xint + 0, yint + 1, p12); 
     get_pixel_clamped(source_image, xint + 1, yint + 1, p22); 
     get_pixel_clamped(source_image, xint + 2, yint + 1, p32); 

     // 4th row 
     get_pixel_clamped(source_image, xint - 1, yint + 2, p03); 
     get_pixel_clamped(source_image, xint + 0, yint + 2, p13); 
     get_pixel_clamped(source_image, xint + 1, yint + 2, p23); 
     get_pixel_clamped(source_image, xint + 2, yint + 2, p33); 

     // interpolate bi-cubically! 
     for (i = 0; i < 3; i++) { 

      float col0 = cubic_hermite(p00[i], p10[i], p20[i], p30[i], xfract); 
      float col1 = cubic_hermite(p01[i], p11[i], p21[i], p31[i], xfract); 
      float col2 = cubic_hermite(p02[i], p12[i], p22[i], p32[i], xfract); 
      float col3 = cubic_hermite(p03[i], p13[i], p23[i], p33[i], xfract); 

      float value = cubic_hermite(col0, col1, col2, col3, yfract); 

      CLAMP(value, 0.0f, 255.0f); 

      sample[i] = (uint8_t)value; 

      printf("sample[%d]=%d\n",i,sample[i]);  

     } 
    } 

3. 「插值助手」

float cubic_hermite(float A, float B, float C, float D, float t) { 

     float a = -A/2.0f + (3.0f*B)/2.0f - (3.0f*C)/2.0f + D/2.0f; 
     float b = A - (5.0f*B)/2.0f + 2.0f*C - D/2.0f; 
     float c = -A/2.0f + C/2.0f; 
     float d = B; 

     return a*t*t*t + b*t*t + c*t + d; 
    } 

    void get_pixel_clamped(PPMImage *source_image, int x, int y, uint8_t temp[]) { 

     CLAMP(x, 0, source_image->x - 1); 
     CLAMP(y, 0, source_image->y - 1); 

     temp[0] = source_image->data[x+(W*y)].red; 
     temp[1] = source_image->data[x+(W*y)].green; 
     temp[2] = source_image->data[x+(W*y)].blue; 
    } 

我已經用here的所有東西上傳了完整的代碼。

執行此代碼時沒有語法錯誤。

但輸出圖像困惑我。

輸入圖像（21x20Pixel）：

該輸入圖像是由2（42x40Pixel）按比例增加：

插值似乎工作在某些點上很好，但圖像看起來像像素被移動。

有人能告訴我我做錯了什麼嗎？ 這個腳本是藉助於： http://blog.demofox.org/2015/08/15/resizing-images-with-bicubic-interpolation/

謝謝你們！

（請不要考慮這個代碼的效率...它aweful我知道）

Answer 1

從您的resize_image（）函數：

destination_image->data[x+((destination_image->y)*y)].red = sample[0]; 

這也許應該是

destination_image->data[x+((destination_image->x)*y)].red = sample[0]; 

什麼幫助調試這種情況是用一些在您的實際數據中不存在的「魔法顏色」初始化您的目標圖像（例如一些可怕的粉紅色:-)）。然後，您可能會注意到resize_image（）調用後，某些目標像素仍具有該顏色。這提示了這個問題。