Java BufferedImage how to know if a pixel is trans

问题:

I'm going to use the getRGB method of BufferedImage. I want to check the pixels of an image and see which of them have transparency (in general the pixels I will have that are transparent will be totaly transparent). How can I get it from the int that getRGB returns?

回答1:

BufferedImage img = ....

public boolean isTransparent( int x, int y ) {
  int pixel = img.getRGB(x,y);
  if( (pixel>>24) == 0x00 ) {
      return true;
  }
}

Of course img has to be in the correct format TYPE_4BYTE_ABGR or some format that supports alpha channels else if will always be opaque (ie 0xff).

回答2:

the correct shift to get alpha value in an int is with >>> due to sign bit.

example: int alpha1 = (pixel1 & 0xff000000) >>> 24;