Java BufferedImage.setRGB在类型13的图像上给出灰度？

Question

I have some manipulation to do on images and I want to show specific parts of the image in a specific color. However, on some image, the color is display in grey.

For exemple, if I write :

BufferedImage baseImage = javax.imageio.ImageIO.read(new File(fileName));
System.out.println(baseImage.getType());
System.out.println(baseImage.getRGB(0, 0));
baseImage.setRGB(0, 0, Color.BLUE.getRGB());
System.out.println(baseImage.getRGB(0, 0));

And that my file is a single pixel in red. The output is :

13
-65536
-16777216

If I save the image, I can see a black pixel.

I tried on an image of the moon which type is 5 instead of 13 in my last example and it works fine.

Am I doing something wrong ?

Answer 1

The buffered image can be of different types as you found out yourself: http://docs.oracle.com/javase/7/docs/api/java/awt/image/BufferedImage.html It depends on the file that is read.

If you require that your buffered image is of a certain type, you need to create the image manually and draw the loaded image into it.

Eg:

BufferedImage loadedImage = ImageIO.read(...);

BufferedImage rgbImage = new BufferedImage(loadedImage.getWidth(), loadedImage.getHeight(), BufferedImage.TYPE_INT_RGB);
rgbImage.getGraphics().drawImage(loadedImage, 0, 0, null);