import java.awt.*;
import java.awt.image.*;

public class Transparency {
  public static Image makeColorTransparent
    (Image im, final Color color) {
    ImageFilter filter = new RGBImageFilter() {
      // the color we are looking for... Alpha bits are set to opaque
      public int markerRGB = color.getRGB() | 0xFF000000;

      public final int filterRGB(int x, int y, int rgb) {
        if ( ( rgb | 0xFF000000 ) == markerRGB ) {
          // Mark the alpha bits as zero - transparent
          return 0x00FFFFFF & rgb;
          }
        else {
          // nothing to do
          return rgb;
          }
        }
      }; 

    ImageProducer ip = new FilteredImageSource(im.getSource(), filter);
    return Toolkit.getDefaultToolkit().createImage(ip);
    }
}

修改代码以使每个像素透明
图片来源：www.example.comhttp://www.rgagnon.com/javadetails/java-0265.html

使用ImageIO.read阅读文件，使用ImageIO.write写入文件。使用BufferedImage的getRGB和setRGB方法更改颜色。

您可以将LookupOp与四分量LookupTable一起使用，该LookupTable将alpha分量设置为零，以获得与背景匹配的颜色。示例可在Using the Java 2D LookupOp Filter Class to Process Images和Image processing with Java 2D中找到。