BufferedImage - greyscale - color information

[AndreB]

Hi,

I read a grey-scale image (sample_image.bmp) and i want to output a colour information.

        public static void main(String[] args) throws Exception {
		BufferedImage bi = ImageIO.read(new File("sample_image.bmp"));
		System.out.println(bi.getRGB(0, 0));
		System.out.println(Integer.toHexString(bi.getRGB(0, 0)));
	}

But now I'm confused. Why isn't the rgb value represents a black colour?
I understand, that the type of the image is TYPE_BYTE_GREY but how can i get the "black" colour information in hex? or how to acquire the value of the grey tone?

Suggestions?

Thanks!

[JosAH]

Did you check the type of your BufferedImage? .bmp format isn't necessarily black and white (although some pictures may look like that).

kind regards,

Jos

[AndreB]

The type of the input image is TYPE_BYTE_GREY.
But why it isnt black? Gimp shows #040404 as a color value (of the pixel [0,0]).
But the output of the HexString is FF222222. That does not look right. The first FF is the A value and thats allright. But the 222222 does not match 040404.

[JosAH]

The type of the input image is TYPE_BYTE_GREY.
But why it isnt black? Gimp shows #040404 as a color value (of the pixel [0,0]).
But the output of the HexString is FF222222. That does not look right. The first FF is the A value and thats allright. But the 222222 does not match 040404.

Hm, your code snippet does make sense and I've seen gimp play funny tricks before and 0x222222 is a very dark gray value ... and I played a bit with your little duck image and that value does make sense: that background value is indeed 0x222222 with full opacity.

kind regards,

Jos

[AndreB]

so gimp isn't right here
*trying irfanview*

thanks!

[AndreB]

hm...

irfanview also says, that RGB: 4,4,4 is right :-(
if i try to copy and write the new image back it is brighter... somehow i don't understand whats going wrong

	public static void main(String[] args) throws Exception {
		BufferedImage bi = ImageIO.read(new File("sample_image.bmp"));
		System.out.println(bi.getRGB(0, 0));
		System.out.println(Integer.toHexString(bi.getRGB(0, 0)));
		
		BufferedImage biCopy = new BufferedImage(bi.getWidth(), bi.getHeight(), BufferedImage.TYPE_INT_RGB);
		for (int x = 0; x < bi.getWidth(); x++) {
			for (int y = 0; y < bi.getHeight(); y++) {
				biCopy.setRGB(x, y, bi.getRGB(x, y));
			}
		}
		ImageIO.write(biCopy, "bmp", new File("sample_out.bmp"));
	}

[AndreB]

Bug ID: 5051418 Grayscale TYPE_CUSTOM BufferedImages are rendered lighter than TYPE_BYTE_GRAY

yay 8[
since 2004 ....

[AndreB]

i hate doing evil hacks :-(

but is there any other options besides THIS:

      public static void main(String[] args) throws Exception {
		BufferedImage bi = ImageIO.read(new File("sample_image.bmp"));
		System.out.println(bi.getRGB(0, 0));
		System.out.println(Integer.toHexString(bi.getRGB(0, 0)));		
		BufferedImage biCopy = new BufferedImage(bi.getWidth(), bi.getHeight(), BufferedImage.TYPE_INT_RGB);

		for (int x = 0; x < bi.getWidth(); x++) {
			for (int y = 0; y < bi.getHeight(); y++) {				
				int gray = bi.getRaster().getPixel(x, y, (int[]) null)[0];
				int rgbVal = (gray << 16) + (gray << 8) + (gray); 
				biCopy.setRGB(x, y, rgbVal);
			}
		}
		ImageIO.write(biCopy, "bmp", new File("sample_out.bmp"));
	}

[JosAH]

i hate doing evil hacks :-(

but is there any other options besides THIS:

There's another workaround in the bug report (see your own link) but then you end up with a LUT image, I don't know it you want that. I never noticed this (old) bug. I opened your image in a MS image manipulation program and indeed it shows a bit darker than it shows up in my Java code; strange ...

kind regards,

Jos