Null Pointer Exception while accessing a function declared inside a class.

newbie2014

Hi I am trying to write a code which detects contours and then blurs ALL of the area outside of the contour. I am attaching my ENTIRE code so that it can be easily debugged.

import gab.opencv.*;

Blurrer b;
OpenCV opencv;
PImage src, canny, scharr, sobel;

void setup() {
  src = loadImage("20.jpg");
  size(src.width, src.height);

  opencv = new OpenCV(this, src);
  opencv.findCannyEdges(150,200);
  canny = opencv.getSnapshot();
  image(canny,0,0);
  loadPixels();

  for (int i = 0; i < width*height; i++) {
          int red = (0xff0000&pixels[i])>>16; // Get red
           int green = (0xff00&pixels[i])>>8; // Get green
           int blue = 0xff&pixels[i]; // Get blue

           if(red>200&&green>200&&blue>200){ pixels[i] = 0xff0000;

           int y = i/width;
           int x = i%width;
           if(x<width/2&&y<height/2) {pixels[i] = 0xff0000; b.blurtopleft(i);}
           else if (x>width/2&& y<height/2) {pixels[i]=0x00ff00;}// blurtopright(i);}
           else if (x<width/2 && y>height/2) {pixels[i] = 0xff;}// blurbottomleft(i);}
           else if (x>width/2 && y>height/2) {pixels[i] = 0xffffff;}// blurbottomright(i);}
  }      }
  updatePixels();



  opencv.loadImage(src);
  opencv.findCannyEdges(100,200);
  //opencv.findScharrEdges(OpenCV.VERTICAL);

  //opencv.findScharrEdges(OpenCV.VERTICAL);
  scharr = opencv.getSnapshot();

}


void draw() {
  pushMatrix();
  scale(0.5);
  //image(src, 0, 0);
//  image(canny, src.width, 0);
  //image(scharr, 0, src.height);
//  image(sobel, src.width, src.height);
  popMatrix();

  text("Source", 10, 25); 
  text("Canny", src.width/2 + 10, 25); 
  text("Scharr", 10, src.height/2 + 25); 
  text("Sobel", src.width/2 + 10, src.height/2 + 25);
}


class Blurrer {
  int pix;
  PImage src = loadImage("20.jpg");
  Blurrer(int p) {
    pix = p;
  }

    void blurtopleft(int pix) {
      image(src,0,0);
      loadPixels();
      int xmax = pix%width;
      int ymax = pix/width;
      for(int i=0; i<pix%width; i++) // in x direction
      {
        for(int j=0; j<pix/width; j++) // in y direction
        {
          if(i==0 && j==0) pixels[j*width+i] = (pixels[((j+1)*width+i)] + pixels[j*width+i+1] + pixels[(j+1)*width+i+1])/3; // topleft corner pixels, average of only 3 surrounding pixels
          else if (i==0 && j>0 && j<ymax) pixels[j*width+i] = (pixels[((j+1)*width+i)] + pixels[j*width+i+1] + pixels[(j+1)*width+i+1] + pixels[(j-1)*width+i] + pixels[(j-1)*width+i+1])/5; // left edge pixels, average of 5 surrounding pixels
          else if (i>0 && j==0 && i<xmax) pixels[j*width+i] = (pixels[((j+1)*width+i)] + pixels[j*width+i+1] + pixels[(j+1)*width+i+1] + pixels[j*width+i-1] + pixels[(j+1)*width+i-1])/5; //top edge pixels, average of 5 surrounding pixels
          else if (i>0 && j>0 && i<xmax && j<ymax) pixels[j*width+i] = (pixels[((j+1)*width+i)] + pixels[j*width+i+1] + pixels[(j+1)*width+i+1] + pixels[j*width+i-1] + pixels[(j+1)*width+i-1] + pixels[(j-1)*width+i-1] + pixels[(j-1)*width+i] + pixels[(j-1)*width+i+1])/8; // center pixels, average of all 8 surrounding pixels
        }
      }
      updatePixels();
    }
  }

So broadly what I am doing is, dividing the entire region into 4 parts and blurring out the topleft region outside of the edge in 1st quadrant, topright to the edge in second quadrant and so on.. I have not written the blurring code for any other quadrant but 1st. I tried to test it but I am getting a null pointer exception.

Can somebody please suggest where I went wrong and what more do I need to declare to get rid of this error. For more insight I am also attaching the image I am working on to ensure we are exactly on the same page. Although I know it is not necessary.

Chrisir

which line is the error?

Chrisir

which line is yellow when you get the error

I had to remove 2(!) } ....................

Chrisir

won't run under processing 3 because of vars in size()

newbie2014

i get a nullpointerexception in line 26 when I try to call b.blurtopleft(i);

U can simply declare size(1280,720) It is running fine if I dont access the class functions. When I run the blurrer function blurtopleft that is when I get an error. Else it is running fine until then

So I believe there's an issue in the way I have declared the function or the class somewhere. Can you have a look at my syntax and let me know if there are any issues with that.

_vk

In a fast look I did not find a line creating b, like b = new Blurrer(x).

So b is null when you try to access it in line 26...

koogs

yes, as _vk suggests

Blurrer b;

is not enough. it defines what type of thing b is, but doesn't create that thing.

Blurrer b = new Blurrer();

this does.

_vk

Note that the constructor defined expects an int to be passed so.

Blurrer b = new Blurrer();

without any value between parenthesis will give you a:

constructor blah is not defined error

Chrisir

it is unnecessary though that the constr has a param because it is passed to the field pix which is then never used (since it is overshadowed by the param pix in the method blurtopleft and not used elsewhere).

Therefore

so this

class Blurrer {
  int pix;
  PImage src = loadImage("20.jpg");
  Blurrer(int p) {
    pix = p;
  }

    void blurtopleft(int pix) {

can be

class Blurrer {

  Blurrer() {
        // empty
  }

    void blurtopleft(int pix) {

(src is also a global image so unnecessary here as well)