gray image log transformation in java -

i trying log transformation gray image. whatever c value black image. idea?

that method:

///---------------------------------------------------

public static bufferedimage log_trans (int[][] imagedata , int c){

        bufferedimage logimage = new bufferedimage(imagedata.length, imagedata[0].length, bufferedimage.type_byte_gray);         double temp;         (int =0 ; i<imagedata.length ; ++){         (int j=0 ; j<imagedata[0].length ; j++){                 int rgb = imagedata[i][j];                 rgb = (rgb<<16)|(rgb<<8)|(rgb);                 temp = math.log10(rgb+1);                 rgb = (int) (c * temp);                  logimage.setrgb(i, j, rgb);         }}          return logimage;     }  -------------------------------------------------------------- public static int[][] readimage(file filename){     bufferedimage img;      try {         img = imageio.read(filename);          // gray_scaled image output          int width = img.getwidth();         int height = img.getheight();         imagepro.fw=width;         imagepro.fh = height;         int [][] readimageval = new int [width][height];         (int = 0; i<height ; i++){             (int j =0  ; j<width ; j++){                  color c = new color(img.getrgb(j, i));                    int r= (int)(c.getred() * 0.299)&0xff;                    int g = (int)(c.getgreen() * 0.587)&0xff;                    int b = (int)(c.getblue() *0.114)&0xff;                    int avg = ((r+b+g));                  readimageval[j][i] = avg;                     }                     }         return readimageval;      } catch (ioexception e) {         // todo auto-generated catch block         e.printstacktrace();     }     return null; } 

it seems "rgb" negative, temp nan, in end "rgb" after:

rgb = (int) (c * temp); 

is 0 , why black picture.

after changing 8th line to:

rgb = (((byte)rgb & 0xff)<<16)|(((byte)rgb & 0xff)<<8)|(((byte)rgb & 0xff));

i dark output, it's not nice. tested value of "c" being 1, 18000, 180000 , 0x00ffffff.