CODEWITHSUNDEEP
javaimage
Brick
Brick

Reputation: 4262

ImageIO writes teal where black expected

I wrote the following simple code to write what should be a small, all black image to disk:

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

public class ImageWriteTest {
    public static void main(String[] args) throws IOException {
        BufferedImage img = new BufferedImage(10, 10, BufferedImage.TYPE_INT_ARGB);
        final int PIXEL = 0xFF_00_00_00; // Black
        for(int i = 0; i < 10; ++i) {
            for(int j = 0; j < 10; ++j) {
                img.setRGB(i, j, PIXEL);
            }
         }

         ImageIO.write(img, "jpg", new File("/tmp/testImage.jpg"));

         int sample = img.getRGB(0,0);
         System.out.println((sample & 0x00_00_00_FF) + "\t" 
             + ((sample & 0x00_00_FF_00) >>> 8) + "\t" 
             + ((sample & 0x00_FF_00_00) >>> 16) + "\t"
             + ((sample & 0xFF_00_00_00) >>> 24));

         Color color = new Color(sample, true);
         System.out.println(color.getGreen() 
             + "\t" + color.getBlue() 
             + "\t" + color.getRed() 
             + "\t" + color.getAlpha());
    }
}

The output to the terminal is two lines

0    0    0   255
0    0    0   255

as I expect.

The image file, however, appears to be a small teal square instead of a small black square, as shown.

Output image from program

That was run on Windows 10 and Java version 1.8.0_92, Java HotSpot. I saw similar results earlier on a Linux machine.

I found two questions that seem somewhat related, but in both of these cases the issue seems to be that a file was read into the program from external source and had extra meta data and/or missing headers. In this case, I created the image programmatically, so I'm expecting it to work.

If I change PIXEL = 0x00_00_00_00; then I do get a black square. That's no doubt a clue, but one that I haven't understood yet. What have I done wrong? How do I fix it?

Upvotes: 0

Views: 111

Answers (1)

Antoniossss
Antoniossss

Reputation: 32517

I am not an expert but this is due to JPG not supporting alpha channels. Change the same result to PNG and it will be as you expected. To do that, simply use 

ImageIO.write(img, "png", file);

After some searching, looks like bug in ImageIO jpeg image color gets drastically changed after just ImageIO.read() and ImageIO.write()

Or maybe not bug after all? Take look here: https://stackoverflow.com/a/39478986/1527544 Comment says, that ARGB for JPG is read as CMYK.

Upvotes: 1

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