How to get average pixel color around defined polygon

Answers

• jeremydouglass

  November 2016 edited November 2016 Answer ✓

  Here is an algorithm for getting the average color of a PImage that was previously posted to the forums:

  color getAverageColor(PImage img) {
    img.loadPixels();
    int r = 0, g = 0, b = 0;
    for (int i=0; i<img.pixels.length; i++) {
      color c = img.pixels[i];
      r += c>>16&0xFF;
      g += c>>8&0xFF;
      b += c&0xFF;
    }
    r /= img.pixels.length;
    g /= img.pixels.length;
    b /= img.pixels.length;
    return color(r, g, b);
  }
  

  Here is one approach to extend this to polygons or arbitrary patterns:

  Step 1. Adapt this function to take two images -- an image, and a mask.

  color getAverageColor(PImage img, PImage mask) { }
  

  The image and the mask are the same size. If the mask pixel is white, include the image pixel color in the average. If not, skip the image pixel.

  https://processing.org/reference/PImage_mask_.html

  Step 2. Then you need a second function, setAverageColor:

  void setAverageColor(PImage img, PImage mask) {
     color c = getAverageColor(img, mask);
     // now loop through and if mask pixel is white change img pixel to c
  }
  

  Now you just have to draw masks (stained glass, whatever) and then use setAverageColor(img,mask) to apply them to your image as color regions.
• cicero38cicero38

  November 2016

  This worked splendidly, thanks jeremy!
• jeremydouglass

  November 2016

  Very glad to hear it, @cicero38cicero38 .

  Do share the demo sketch (and / or upload an image of the output) if you want others to see how your stained glass worked out. I know I'm curious!