Reputation: 413
I'm trying to convert from RGB to GrayScale Image.
The method that does this task is the following:
public BufferedImage rgbToGrayscale(BufferedImage in)
{
int width = in.getWidth();
int height = in.getHeight();
BufferedImage grayImage = new BufferedImage(width, height, BufferedImage.TYPE_BYTE_GRAY);
WritableRaster raster = grayImage.getRaster();
int [] rgbArray = new int[width * height];
in.getRGB(0, 0, width, height, rgbArray, 0, width);
int [] outputArray = new int[width * height];
int red, green, blue, gray;
for(int i = 0; i < (height * width); i++)
{
red = (rgbArray[i] >> 16) & 0xff;
green = (rgbArray[i] >> 8) & 0xff;
blue = (rgbArray[i]) & 0xff;
gray = (int)( (0.30 * red) + (0.59 * green) + (0.11 * blue));
if(gray < 0)
gray = 0;
if(gray > 255)
gray = 255;
outputArray[i] = (gray & 0xff);
}
}
raster.setPixels(0, 0, width, height, outputArray);
return grayImage;
}
I have a method that saves the pixels value in a file:
public void writeImageValueToFile(BufferedImage in, String fileName)
{
int width = in.getWidth();
int height = in.getHeight();
try
{
FileWriter fstream = new FileWriter(fileName + ".txt");
BufferedWriter out = new BufferedWriter(fstream);
int [] grayArray = new int[width * height];
in.getRGB(0, 0, width, height, grayArray, 0, width);
for(int i = 0; i < (height * width); i++)
{
out.write((grayArray[i] & 0xff) + "\n");
}
out.close();
} catch (Exception e)
{
System.err.println("Error: " + e.getMessage());
}
}
The problem that I have is that, the RGB value I get from my method, is always bigger than the expected one.
I created an image and I filled it with color 128, 128, 128. According to the first method, if I print the outputArray's data, I get:
r, g, b = 128, 128, 128. Final = 127 ---> correct :D
However, when I called the second method, I got the RGB value 187 which is incorrect.
Any suggestion?
Thanks!!!
Upvotes: 0
Views: 380
Reputation: 341
Take a look at javax.swing.GrayFilter
, it uses the RBGImageFilter
class to accomplish the same thing and has very similar implementation. It may make your life simpler.
Upvotes: 1
Reputation: 6652
I'm not an expert at these things but aren't RGB values stored as hex (base16)? If so, theproblem lies in your assumption that the operation & 0xff
will cause your int
to be stored/handled as base16. It is just a notation and default int
usage in strings will always be base10.
int a = 200;
a = a & 0xff;
System.out.println(a);
// output
200
You need to use an explicit base16 toString() method.
System.out.println(Integer.toHexString(200));
// output
c8
Upvotes: 0