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Better handling of edge-cases for bilinear resampler
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mhugent committed Dec 28, 2011
1 parent cb7b812 commit bccba1d
Showing 1 changed file with 57 additions and 25 deletions.
82 changes: 57 additions & 25 deletions src/core/raster/qgsbilinearrasterresampler.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@

#include "qgsbilinearrasterresampler.h"
#include <QImage>
#include <cmath>

QgsBilinearRasterResampler::QgsBilinearRasterResampler()
{
Expand All @@ -33,43 +34,74 @@ void QgsBilinearRasterResampler::resample( const QImage& srcImage, QImage& dstIm

double currentSrcRow = nSrcPerDstY / 2.0 - 0.5;
double currentSrcCol;
int currentSrcRowInt, currentSrcColInt;
double u, v;

QRgb px1, px2, px3, px4;

for ( int i = 0; i < dstImage.height(); ++i )
{
//avoid access to invalid rows
if ( currentSrcRow < 0 )
{
currentSrcRow += nSrcPerDstY;
}

currentSrcCol = nSrcPerDstX / 2.0 - 0.5;
currentSrcRowInt = floor( currentSrcRow );
v = currentSrcRow - currentSrcRowInt;

for ( int j = 0; j < dstImage.width(); ++j )
{
double u = currentSrcCol - ( int )currentSrcCol;
double v = currentSrcRow - ( int )currentSrcRow;
if ( currentSrcCol > srcImage.width() - 2 )
{
//resample in one direction only
px1 = srcImage.pixel( currentSrcCol, currentSrcRow );
px2 = srcImage.pixel( currentSrcCol, currentSrcRow + 1 );
dstImage.setPixel( j, i, resampleColorValue( v, px1, px2 ) );
currentSrcCol += nSrcPerDstX;
continue;
}
else if ( currentSrcRow > srcImage.height() - 2 )
currentSrcColInt = floor( currentSrcCol );
u = currentSrcCol - currentSrcColInt;

//handle eight edge-cases
if( currentSrcRowInt < 0 || currentSrcRowInt >= (srcImage.height() - 1) || currentSrcColInt < 0 || currentSrcColInt >= (srcImage.width() - 1) )
{
px1 = srcImage.pixel( currentSrcCol, currentSrcRow );
px2 = srcImage.pixel( currentSrcCol + 1, currentSrcRow );
dstImage.setPixel( j, i, resampleColorValue( u, px1, px2 ) );
//pixels at the border of the source image needs to be handled in a special way
if( currentSrcRowInt < 0 && currentSrcColInt < 0 )
{
dstImage.setPixel( j, i, srcImage.pixel(0, 0) );
}
else if( currentSrcRowInt < 0 && currentSrcColInt >= ( srcImage.width() - 1 ) )
{
dstImage.setPixel( j, i, srcImage.pixel( srcImage.width() - 1, 0 ) );
}
else if( currentSrcRowInt >= (srcImage.height() - 1) && currentSrcColInt >= ( srcImage.width() - 1 ) )
{
dstImage.setPixel( j, i, srcImage.pixel( srcImage.width() - 1, srcImage.height() - 1 ) );
}
else if( currentSrcRowInt >= (srcImage.height() - 1) && currentSrcColInt < 0 )
{
dstImage.setPixel( j, i, srcImage.pixel( 0, srcImage.height() - 1 ) );
}
else if( currentSrcRowInt < 0 )
{
px1 = srcImage.pixel( currentSrcColInt, 0 );
px2 = srcImage.pixel( currentSrcColInt + 1, 0 );
dstImage.setPixel( j, i, resampleColorValue( u, px1, px2 ) );
}
else if( currentSrcRowInt >= (srcImage.height() - 1) )
{
px1 = srcImage.pixel( currentSrcColInt, srcImage.height() - 1 );
px2 = srcImage.pixel( currentSrcColInt + 1, srcImage.height() - 1 );
dstImage.setPixel( j, i, resampleColorValue( u, px1, px2 ) );
}
else if( currentSrcColInt < 0 )
{
px1 = srcImage.pixel( 0, currentSrcRowInt );
px2 = srcImage.pixel( 0, currentSrcRowInt + 1);
dstImage.setPixel( j, i, resampleColorValue( v, px1, px2 ) );
}
else if( currentSrcColInt >= ( srcImage.width() - 1 ) )
{
px1 = srcImage.pixel( srcImage.width() - 1, currentSrcRowInt );
px2 = srcImage.pixel( srcImage.width() - 1, currentSrcRowInt + 1);
dstImage.setPixel( j, i, resampleColorValue( v, px1, px2 ) );
}
currentSrcCol += nSrcPerDstX;
continue;
}
px1 = srcImage.pixel( currentSrcCol, currentSrcRow );
px2 = srcImage.pixel( currentSrcCol + 1, currentSrcRow );
px3 = srcImage.pixel( currentSrcCol + 1, currentSrcRow + 1 );
px4 = srcImage.pixel( currentSrcCol, currentSrcRow + 1 );

px1 = srcImage.pixel( currentSrcColInt, currentSrcRowInt );
px2 = srcImage.pixel( currentSrcColInt + 1, currentSrcRowInt );
px3 = srcImage.pixel( currentSrcColInt + 1, currentSrcRowInt + 1 );
px4 = srcImage.pixel( currentSrcColInt, currentSrcRowInt + 1 );
dstImage.setPixel( j, i, resampleColorValue( u, v, px1, px2, px3, px4 ) );
currentSrcCol += nSrcPerDstX;
}
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