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BilinearInterpolation.java
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package com.example.jnibitmapoperationstest;
import android.graphics.Bitmap;
import android.graphics.Color;
/** class for resizing imageData using the Bilinear Interpolation method */
public class BilinearInterpolation
{
/** the method for resizing the imageData using the Bilinear Interpolation algorithm */
public static void resize(final Bitmap input,final Bitmap output)
{
final int oldHeight=input.getHeight(),oldWidth=input.getWidth();
final int newHeight=output.getHeight(),newWidth=output.getWidth();
// position of the top left pixel of the 4 pixels to use interpolation on
int xTopLeft,yTopLeft;
int x,y,lastTopLefty;
final float xRatio=(float)newWidth/(float)oldWidth,yratio=(float)newHeight/(float)oldHeight;
// Y color ratio to use on left and right pixels for interpolation
float ycRatio2=0,ycRatio1=0;
// pixel target in the src
float xt,yt;
// X color ratio to use on left and right pixels for interpolation
float xcRatio2=0,xcratio1=0;
int rgbTopLeft=0,rgbTopRight=0,rgbBottomLeft=0,rgbBottomRight=0,rgbTopMiddle=0,rgbBottomMiddle=0;
// do the resizing:
for(x=0;x<newWidth;x++)
{
xTopLeft=(int)(xt=x/xRatio);
// when meeting the most right edge, move left a little
if(xTopLeft>=oldWidth-1)
xTopLeft--;
if(xt<=xTopLeft+1)
{
// we are between the left and right pixel
xcratio1=xt-xTopLeft;
// color ratio in favor of the right pixel color
xcRatio2=1-xcratio1;
}
for(y=0,lastTopLefty=Integer.MIN_VALUE;y<newHeight;y++)
{
yTopLeft=(int)(yt=y/yratio);
// when meeting the most bottom edge, move up a little
if(yTopLeft>=oldHeight-1)
yTopLeft--;
// we went down only one rectangle
if(lastTopLefty==yTopLeft-1)
{
rgbTopLeft=rgbBottomLeft;
rgbTopRight=rgbBottomRight;
rgbTopMiddle=rgbBottomMiddle;
rgbBottomLeft=input.getPixel(xTopLeft,yTopLeft+1);
rgbBottomRight=input.getPixel(xTopLeft+1,yTopLeft+1);
rgbBottomMiddle=Color.argb((int)(Color.alpha(rgbBottomLeft)*xcRatio2+Color.alpha(rgbBottomRight)*xcratio1),//
(int)(Color.red(rgbBottomLeft)*xcRatio2+Color.red(rgbBottomRight)*xcratio1),//
(int)(Color.green(rgbBottomLeft)*xcRatio2+Color.green(rgbBottomRight)*xcratio1),//
(int)(Color.blue(rgbBottomLeft)*xcRatio2+Color.blue(rgbBottomRight)*xcratio1));
}
else if(lastTopLefty!=yTopLeft)
{
// we went to a totally different rectangle (happens in every loop start,and might happen more when making the picture smaller)
rgbTopLeft=input.getPixel(xTopLeft,yTopLeft);
rgbTopRight=input.getPixel(xTopLeft+1,yTopLeft);
rgbTopMiddle=Color.argb((int)(Color.alpha(rgbTopLeft)*xcRatio2+Color.alpha(rgbTopRight)*xcratio1),//
(int)(Color.red(rgbTopLeft)*xcRatio2+Color.red(rgbTopRight)*xcratio1),//
(int)(Color.green(rgbTopLeft)*xcRatio2+Color.green(rgbTopRight)*xcratio1),//
(int)(Color.blue(rgbTopLeft)*xcRatio2+Color.blue(rgbTopRight)*xcratio1));
rgbBottomLeft=input.getPixel(xTopLeft,yTopLeft+1);
rgbBottomRight=input.getPixel(xTopLeft+1,yTopLeft+1);
rgbBottomMiddle=Color.argb((int)(Color.alpha(rgbBottomLeft)*xcRatio2+Color.alpha(rgbBottomRight)*xcratio1),//
(int)(Color.red(rgbBottomLeft)*xcRatio2+Color.red(rgbBottomRight)*xcratio1),//
(int)(Color.green(rgbBottomLeft)*xcRatio2+Color.green(rgbBottomRight)*xcratio1),//
(int)(Color.blue(rgbBottomLeft)*xcRatio2+Color.blue(rgbBottomRight)*xcratio1));
}
lastTopLefty=yTopLeft;
if(yt<=yTopLeft+1)
{
// color ratio in favor of the bottom pixel color
ycRatio1=yt-yTopLeft;
ycRatio2=1-ycRatio1;
}
// prepared all pixels to look at, so finally set the new pixel data
output.setPixel(x,y,Color.argb(//
(int)(Color.alpha(rgbTopMiddle)*ycRatio2+Color.alpha(rgbBottomMiddle)*ycRatio1),//
(int)(Color.red(rgbTopMiddle)*ycRatio2+Color.red(rgbBottomMiddle)*ycRatio1),//
(int)(Color.green(rgbTopMiddle)*ycRatio2+Color.green(rgbBottomMiddle)*ycRatio1),//
(int)(Color.blue(rgbTopMiddle)*ycRatio2+Color.blue(rgbBottomRight)*ycRatio1)));
}
}
}
}