java - How to convert an image to a 0-255 grey scale image -

i want convert image gray scale image pixel intensities between 0-255.

i able convert images gray scale images following java method.

public void converttograyscale(bufferedimage bufimage, int imgwidth, int imgheight) {      (int w = 0; w < imgwidth; w++) {         (int h = 0; h < imgheight; h++) {              color color = new color(bufimage.getrgb(w, h));             int colavgval = ((color.getred() + color.getgreen() + color.getblue()) / 3);             color avg = new color(colavgval, colavgval, colavgval);              bufimage.setrgb(w, h, avg.getrgb());              system.out.println(avg.getrgb());         }     } } 

"system.out.println(avg.getrgb());" used see pixel intensities all grey levels minus values , not between 0-255.

am doing wrong ? how convert image gray scale image pixel intensities between 0-255.

thanks

color.getrgb() not return value 0..255, returns integer composited of red, green , blue values, including alpha value. presumably, alpha value 0xff, makes any combined color end 0xffrrggbb, or, got, huge negative number when written in decimals.

to see "gray" level assigned, check colavgval.

note better formula convert between rgb , grayscale use pal/ntsc conversion:

gray = 0.299 * red + 0.587 * green + 0.114 * blue 

because "full blue" should darker in grayscale "full red" , "full green".

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note: if use formula directly, watch out floating point rounding errors. in theory, should not return value outside of 0..255 gray; in practice, it will. test , clamp result.

another option not require testing-and-clamping per pixel, use integer-only version:

gray = (299 * red + 587 * green + 114 * blue)/1000; 

which should work small rounding error.