Filters for an Image

[RPBLEA]

K i'm having a small problem, I have a filter that can take out pixels from the picture and that's shown down below. I can't figure out how to alter the filter to make the image black and white, I figure I have to change the value by subtracting 255 by the old value, Can't figure out how to do it? any ideas


package filters;
import imagelab.*;
import javax.swing.JOptionPane;

public class Mesh implements ImageFilter {

ImgProvider filteredImage;

public void filter (ImgProvider ip) {
short tmp;
short [][] al = ip.getAlpha();
int npixels = getMeshSize();
for (int r = 0; r<al.length; r++) {
for (int c=0; c<al[0].length; c++) {
if ((c/npixels+r/npixels) % 2 == 1) al[r][c] = 0;
}//for c
}//for r;
filteredImage = new ImgProvider();
filteredImage.setColors(ip.getRed(), ip.getGreen(), ip.getBlue(), al);
filteredImage.showPix("Transparent");
}//filter

public ImgProvider getImgProvider() {
return filteredImage;
}//getImgProvider

public String getMenuLabel() {
return "Mesh";
} //getMenuLabel

protected int getMeshSize() {
String response = JOptionPane.showInputDialog(null, "Enter Mesh Size", "");
int num;
try {
num = Integer.parseInt(response);
if (num <= 0) num = 2;
} catch (NumberFormatException ex) {
num = 2;
}//catch
return num;
}//getMeshSize

}

[Phaelax]

Do you want a b&w image? or a greyscale image?

for greyscale:
add the 3 color components together, then divide by 255. then use that value for all the color channels of the pixel

for b&w:
if the image is in greyscale mode, just check the color value of the pixel. if its less than 128, make it black. if its greater that 128, make it white.

[RPBLEA]

How can I code from this filter a black and white image? can't figure it out, I know I have to subtract by 255 and loop through the array but can't get the for loop to work?

[cjard]

Originally posted by Phaelax
Do you want a b&w image? or a greyscale image?

for greyscale:
add the 3 color components together, then divide by 255. then use that value for all the color channels of the pixel

im not sure i agree with div by 255.. div by 3 more like, to give the average value!

note though that the human eye is less sensitive to blue than other colours.. i suggest reading about yuv 422 and other such things.. youll get a be3tter idea of how to convert to grayscale. black and white are affected by similar issues..

[Phaelax]

oops, yea divide by 3. After cjard mentioned the eye's sensitivity is different with each color, I remembered an image library I worked on with someone else. Here's what we did:

r = red * 0.3
g = green *0.59
b = blue *0.11
grey = r + g + b