Hello,
This is a baffling problem first reported by Hitoshi Sato of IBM-Japan
some 2-3 weeks ago on this mailing list. It seems like there is a
problem using bilinear interpolation on a Buffered Image under some
special circumstances. The circumstances are ...
1) The BufferedImage is a TYPE_INT_ARGB
2) A rectangle is filled with a completely transparent color (say white,
although it behaves the same with any color)
3) A smaller rectangle is filled over the top of it using a completely
opaque color (also white)
4) The BufferedImage is then scaled by a factor of 2.0 with Bilinear
interpolation using an AffineTransformOp.
5) The resulting BufferedImage is then drawn in a JFrame with a white
background.
The result is a gray border around the form of the smaller rectangle.
If the alpha of the outer rectangle is changed to be even 1, the effect
goes away. Does any have a clue as to why this should be the behavior??
Hitoshi's code is found below.
package test;
/**
* Interpolation test code.
* visualizer edition
*/
import java.awt.*;
import java.awt.geom.*;
import java.awt.image.*;
import java.awt.event.*;
import javax.swing.*;
public class VInterpolationTest extends JFrame {
BufferedImage bi;
/**
*/
VInterpolationTest(BufferedImage bi) {
this.bi = bi;
}
/**
*/
public static void main(String[] args) {
BufferedImage src = createTestImage(200, 200);
BufferedImage result = resize(src, 2.0, 2.0,
AffineTransformOp.TYPE_BILINEAR);
VInterpolationTest test = new VInterpolationTest(result);
test.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e)
{System.exit(0);}
});
test.setSize(600, 500);
test.show();
}
/**
*/
public void paint(Graphics g) {
Graphics2D g2 = (Graphics2D)g;
g2.setColor(new Color(255,255,255,255));
g2.fillRect(0, 0, getWidth(), getHeight());
g2.drawImage(this.bi, null, 0, 0);
}
/**
*/
static BufferedImage createTestImage(int width, int height) {
BufferedImage bi = new BufferedImage(width, height,
BufferedImage.TYPE_INT_ARGB);
Graphics2D g2 = bi.createGraphics();
Color outer = new Color(255, 255, 255, 0);
Color inner = new Color(255, 255, 255, 255);
g2.setColor(outer);
g2.fillRect(0, 0, width, height);
g2.setColor(inner);
g2.fillRect(width/4, height/4, width/2, height/2);
return bi;
}
/**
*/
static BufferedImage resize(BufferedImage bi,
double scaleX, double scaleY, int interpolation) {
AffineTransform at =
AffineTransform.getScaleInstance(scaleX,
scaleY);
AffineTransformOp ato =
new AffineTransformOp(at, interpolation);
return ato.filter(bi, null);
}
}
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