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.
