Color Substitution
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Color Substitution: Filtering an image can allow you to
produce a number of interesting effects. Color substitution is one of the
simplest effects. Basically what you do for color substitution is test the
pixels for a file and change the ones which have a certain value to a
different value. An explanation of how this is done appear below.
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Step One: Import the java.awt.image.*; package. This will be
necessary so you can use the PixelGrabber and MemoryImageSource classes.
Step Two: Declare some instances of the image class outside of
the init method and then in the init method load one image and call a
function to create the other(s) like this:
c=getImage(getDocumentBase(), "cards/JS.gif");
red=makeAlt(Color.red.getRGB());
Step Three: Here's the makeAlt function:
<![CDATA[
public Image makeAlt(int color){
Image temp=null;
try{
int pixel[] = new int[w*h];
PixelGrabber pg = new PixelGrabber(c, 0, 0, w, h, pixel, 0, w);
if(pg.grabPixels() &&((pg.status() & ImageObserver.ALLBITS) != 0)){
for(int x = 0; x< w * h; x++){
int r = (pixel[x] & 0x00ff0000)>>16;
int g = (pixel[x] & 0x0000ff00)>>8;
int b = (pixel[x] & 0x000000ff);
if(r<100 && g<100 && b<100){
pixel[x]= color;;
}
}
temp=createImage(new MemoryImageSource(w, h, pixel, 0, w));
}
}catch(InterruptedException e) { }
return temp;
}
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First of all you will notice that it returns an Image and that it takes and
integer value representing a color as a parameter. After declaring a
variable called temp you encounter a try-catch block. The purpose of this
block is to deal with any errors which might occur when the PixelGrabber
methods are called. Elsewhere in your program values for w and h must be
declared (they should be set to the dimensions of the image loaded into the
variable called c). Before you can call the PixelGrabber constructor you
must have an array of ints (called pixel in this example). The grabPixels
method actually places all the values of the pixels in the int array. Once
this is accomplished you are ready to start filtering.
The for loop iterates through all the pixel values stored in pixel and tests
them one at a time. In this case we're looking for black pixels (or anything
that's pretty dark -- with red, green, and blue values all less than 100).
If we find such a pixel we will change it to the color value stored in the
variable color. After that it's just a matter of creating an image and
returning its value to the calling function.