resize vertically is not working properly

Question

i take the re-copy approach guys and badly stuck in that problem .. everything my code is fine just writing pixel is wrong somewhere. i'm posting my writing snippet of my resize please give me some hints for that.

// here is my code for writing pixels using re-copy approach . please help

  for ( int i = 0 , biHeight = abs ( bi_new.biHeight ) ; i < biHeight ; i++ ) 
  {
     for ( int j = 0 ; j < bi_new.biWidth ; j++ ) 
     {
        // temp storage 
        RGBTRIPLE triple ;

        // read from infile 
        fread ( &triple , sizeof ( RGBTRIPLE ) , 1 , inptr ) ;

        // write to outfile 
        fwrite ( &triple , sizeof ( RGBTRIPLE ) * size , 1 , outptr ) ;
     }

     // add padding 
     for ( int k = 0 ; k < padding_new ; k++ )
     {
        fputc ( 0x00 , outptr ) ;
     }
     // skip over padding if any 
     fseek ( inptr , padding_old , SEEK_CUR ) ;
     if ( size != 1 ) 
     {
     // write vertical pixels
     fseek ( inptr , bi.biWidth , SEEK_SET ) ;
     for ( int l = 0 ; l < bi_new.biWidth ; l++ ) 
     {
       //temp storage
       RGBTRIPLE triple1;

       // read from inline
       fread ( &triple1 , sizeof ( RGBTRIPLE ) , 1 , inptr ) ;

       // write to outfile 
       fwrite ( &triple1 , sizeof ( RGBTRIPLE ) * size , 1 , outptr ) ;
     }
     //add padding 
     for ( int m = 0 ; m < padding_new ; m++ ) 
     {
        fputc ( 0x00 , outptr ) ;
     }
     // skip over padding
     fseek ( inptr , padding_old , SEEK_CUR ) ;

   }
}

Answer 1

Why are you vertically resizing twice? Your nested for loop at the top should take care of both your vertical and horizontal iterations. The other for loop you have at the bottom appears completely redundant.

When writing the rgb triple, unfortunately you can't just say, "write it *4 times". C isn't that smart. It writes it once and then fills the other 3 times with garbage values or unknown values...which is why your colors are strange.

To resize, pseudocode below:

//iterate over infile scanlines for loop
    //for loop for vertical resize   
       //if this isn't the first time through this row to resize vertically
          //use fseek to reset the cursor back to the start of the row
       //for loop for horizontal resize
          //read a single RGB triple in
          //for loop to write that triple n number of times
          //add new padding
//skip old padding