ADDITIONAL SYSTEM INFORMATION :
java version "1.8.0_271"
Java(TM) SE Runtime Environment (build 1.8.0_271-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.271-b09, mixed mode)

Bug occurred on OSX as well as on CentOS.

A DESCRIPTION OF THE PROBLEM :
The java.awt.image.RescaleOp class produces incorrect results for certain PNG images.

The operation is applied only to a subset of the source image, with greyed out background where a transparent background is expected.

With Oracle JDK 1.8.0_251 the results are still as expected.

This bug occurred with a PNG encoded source image with transparent background.


REGRESSION : Last worked in JDK 1.8.0_251

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
See https://github.com/agawecki/java-rescale-op-test



EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Rescale operation applied homogeneously to source image and leaves the transparent background intact.
ACTUAL -
The rescale operation is applied to a subset of the source image and garbles the transparent background.

---------- BEGIN SOURCE ----------
package test;

import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.awt.image.RescaleOp;
import java.io.File;

public class Main {

  public static void main(String[] args) {
    System.out.println(System.getProperty("java.version"));

    String imageFileName = "test.png";
    try {
      File imageFile = new File(imageFileName);
      BufferedImage image = ImageIO.read(imageFile);
      rescale(image, 1.0f, 50.0f);

      File outputFile = new File(imageFile.getParent(), "rescaled-" + imageFile.getName());
      ImageIO.write(image, "png", outputFile);
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  static BufferedImage rescale(BufferedImage img,
                               float factor,
                               float offset) {
    RescaleOp rescaleOp = new RescaleOp(factor, offset, null);
    return rescaleOp.filter(img, img);
  }
}

---------- END SOURCE ----------

FREQUENCY : always