Java beginner: convert an image to a binary array

Question

this is what I've gone so far and I can't seem to go further because I don't understand bitwise operations on the RGB

// Read from a file
File file = new File("src/a.gif");
image = ImageO.read(file);
int[] rgbarr = image.getRGB(0, 0, 13, 15, null, 0, 13);// image is 13*15 
System.out.println(rgbarr.length);
for (int i : rgbarr)
    {
        System.out.println(i);
    }

Output: was values such as -16777216 and -1 Because I've already made an image black and white just to ease my understanding

But in our case here let's suppose it would be just random image , how do I get from normal RGB image to binary values (0 or 1) for each pixel.

KitsuneYMG · Accepted Answer · 2011-01-22 23:55:05Z

2

I'm betting that each int in the array is a packed ARGB value;

boolean [] output = new boolean[rgbarr.length];
for ( int i=0; i<rgbarr.length; ++i ) {
  int a = (rgbarr[i] >> 24 ) & 0x0FF;
  int r = (rgbarr[i] >> 16 ) & 0x0FF;
  int g = (rgbarr[i] >> 8  ) & 0x0FF;
  int b = (rgbarr[i]       ) & 0x0FF;
  output[i] = (0.30*r + 0.59*g + 0.11*b) > 127;
}

The output equation I choose was taken from a definition of Luminance from wikipedia. You can change the scales so long as the coefficients add up to 1.

edited Jan 22, 2011 at 23:55

answered Jan 22, 2011 at 19:56

KitsuneYMG

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1 Comment

Ismail Marmoush Over a year ago

the 127 made it all false, I tried (1) and it worked fine, donno why though :)

Chris Dennett · Accepted Answer · 2011-01-22 20:28:54Z

1

You can do some thing like this,

BufferedImage img = (BufferedImage) image;
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ImageIO.write(img , "jpg", baos);
byte[] previewByte = baos.toByteArray();

Hope this helps!!

edited Jan 22, 2011 at 20:28

Chris Dennett

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answered Jan 22, 2011 at 20:10

user405398

Comments

Hlavac · Accepted Answer · 2011-01-22 19:56:08Z

0

You already have RGB values in the int[], that is color of each pixel. You could compare this to a specific background color, like black, to get a 1-bit pixel value. Then maybe set a bit in another appropriately sized byte[] array...

answered Jan 22, 2011 at 19:56

Hlavac

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