[JAVA] How to make an image partially transparent in Processing


Even if I answered the question more than half a year ago on the QA site, I was sad that no one saw it, so I will post it.

Thing you want to do

I want to read image data with Processing and make an arbitrary area transparent with an arbitrary amount of transparency.


The code is below. It is a tricky technique to extract the color of each pixel of the image, set the amount of transparency, and then draw each pixel. I use ellipse when drawing pixels, but you can also use rect or spot. .. When using spot, the transparency setting uses stroke instead of fill.

PImage img;
int imgWidth, imgHeight;

//Range you want to be transparent
int xstart = 100;
int xstop = 200;
int ystart = 50;
int ystop = 100;
//Permeation amount
int tpSet = 100;

void setup() {
  size(480, 320);
  img = loadImage("imgName");
  imgWidth = img.width;
  imgHeight = img.height;

void draw() {
  for (int x =0; x<imgWidth; x++) {
    for (int y=0; y<imgHeight; y++) {
      //x,If y is the selected range, make it transparent.
      color imgColor = img.get(x,y);
      if(x>xstart && x<xstop && y>ystart && y<ystop){
        fill(imgColor, tpSet);
      ellipse(x, y, 1, 1);//May be rect

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