Basic Question: Detecting Black Pixels in a Picture.

PixelMx

Hello. I'm new to processing and I decided to start with a simple script: something that allows me to identify black pixels in a picture. I have the code included below and as a checker I included the print command, just to see if the coordinates were moving forward (for loops).

Nothing is printing in my console and nothing is showing in my sketch, what am I doing wrong? Thanks in advance

void setup(){
  PImage myImage = loadImage("test.jpg");
  loadPixels();
  size(myImage.width,myImage.height);

}

void draw(){
  for (int i = 0; i < width; i++) {
    for (int j = 0; j < height; i++){
      color c = get(i,j);
      if (c == color(0)){
        point(i,j);
        print(i+","+j);
      }
    }
  }
}

PixelMx

Nevermind, I found the error, problem was I was using i++ for both width and height, I made some changes to the code:

void setup(){
  size(1920,1080);
  background(255);
  color(0);
}

void findBlack(){
  PImage myImage = loadImage("test.jpg");
  loadPixels();
  int count =0;
  for (int i = 0; i < width; i++) {
    for (int j = 0; j < height; j++){

      print("("+i+","+j+")");
      color c = myImage.get(i,j);
      if (c == color(0)){

       rect(i,j,3,3,1);
       saveFrame(count+".png");
       count++;

      }
    }
  }
}

void draw(){
  findBlack();

}

koogs

Warning: calling println too much can cause real problems

Draw is being called up to 60 times a second. You probably don't want this. So use noLoop()

PixelMx

Thanks @koogs. I uploaded the resutl here: https://www.youtube.com/watch?v=cLZt0GYTxzw

koogs

Post the changed code. I think there are some serious inefficiencies in your code still, based on the YouTube clip.

quark

Also you don't want to load the image OR calculate color(0) Or for every pixel. Try this

PImage myImage ;

void setup(){
  size(1920,1080);
  myImage = loadImage("test.jpg");  
  background(255);
  color(0);
}

void findBlack(){
  loadPixels();
  int count =0;
  int fc = color (0);
  for (int i = 0; i < width; i++) {
    for (int j = 0; j < height; j++){

      print("("+i+","+j+")");
      color c = myImage.get(i,j);
      if (c == fc){

       rect(i,j,3,3,1);
       saveFrame(count+".png");
       count++;
      }
    }
  }
}

void draw(){
  findBlack();
}

PixelMx

Thanks Quark, I'll try that!

Koogs, Here's my final code, before Quark's comments:

void setup(){
  size(1920,1080);
  background(255);
  color(0);
}

void findBlack(){
  PImage myImage = loadImage("test.jpg");
  loadPixels();
  int count =0;
  for (int i = 0; i < width; i=i+3) {
    for (int j = 0; j < height; j=j+3){

      color c = myImage.get(i,j);
      if (c == color(0)){

       rect(i,j,3,3,1);
       saveFrame(count+".png");
       count++;

      }
    }
  }
}

void draw(){
  findBlack();

}

PixelMx

Also, before reading your previous comments, I went ahead and did some more changes. Now, instead of replacing black pixels with a rect, I'm replacing pixels with fonts and using the original image's color as reference.

    void setup(){
      size(736,732);
      background(255);
      PFont font;
      font = loadFont("CourierNewPS-BoldMT-10.vlw");
      textFont(font);
    }

    void findBlack(){
      PImage myImage = loadImage("test.jpg");
      loadPixels();
      int count =0000;
        char batman[] = {'H', 'A', '!', 'H', 'A', '!', 'H', 'A', '!', '*','*'};
            int co = 0;
      for (int j = 0; j < width; j=j+7) {
        for (int i = 0; i < height; i=i+7){


          color c = myImage.get(i,j);
          if (c != color(255)){
           fill(c);
           textSize(10); 
           text(batman[co],i,j);
           if (co == 10){
             co = 0;
           }
           else {
             co++;
           }
           saveFrame("Batman"+count+".png");
           count++;

          }
        }
      }
    }

    void draw(){
      findBlack();
      noLoop();
    } 

The result: https://drive.google.com/file/d/0BwTV1gIcOedwLXdPUzE0cUQyWUU/view?usp=sharing