Generating Picture - Black And White Sketch

I'm stuck with a problem. The code below generates a coloured image.

//Setting the size of the graphics window
final int WINDOW_DIMENSION = 200;
final int SIZE_FACTOR = 3;
EasyGraphics generate = new EasyGraphics(WINDOW_DIMENSION*SIZE_FACTOR,WINDOW_DIMENSION*SIZE_FACTOR);
 
//Constructing the arrays
char[][] firstArray = new char[WINDOW_DIMENSION][WINDOW_DIMENSION];
char[] secondArray = scan.toCharArray();
 
[Code] ...

What I would like to do is generate a picture which is mostly white but the colour boundaries of the original picture are in black. I tried using the code below but it doesn't produce what I wanted.

for (int a = 1; a < WINDOW_DIMENSION; a++) {
for (int b = 1; b < WINDOW_DIMENSION; b++) {
generate.setColor(0,0,0);
if(firstArray[a][b]!=firstArray[a-1][b] || firstArray[a][b]!=firstArray[a][b-1])
generate.setColor(255,255,255);
generate.plot(a,b);
}
}