Sometimes, we want to check if a specific pixel of an image is transparent with JavaScript.

In this article, we’ll look at how to check if a specific pixel of an image is transparent with JavaScript.

How to check if a specific pixel of an image is transparent with JavaScript?

To check if a specific pixel of an image is transparent with JavaScript, we can put the image in a canvas and then get the pixel data from the canvas.

For instance, we write

const img = document.getElementById("my-image");
const canvas = document.createElement("canvas");
canvas.width = img.width;
canvas.height = img.height;
canvas.getContext("2d").drawImage(img, 0, 0, img.width, img.height);

to select the image with getElementById.

And then we create a canvas with createElement.

We then set the canvas dimensions with

canvas.width = img.width;
canvas.height = img.height;

And then we call canvas.getContext("2d").drawImage to put the image into the canvas.

Next, in a click handler, we write

const pixelData = canvas
  .getContext("2d")
  .getImageData(event.offsetX, event.offsetY, 1, 1).data;

to get the clicked pixel’s data.

data is an array with the rgba values.

And we can get the transparency value from the last value, which is the a value.

Conclusion

To check if a specific pixel of an image is transparent with JavaScript, we can put the image in a canvas and then get the pixel data from the canvas.