Transparent PNG Image Copied to Clipboard Renders with Black Background

Question

I'm encountering an issue with a JavaScript function in a web application. The function copies a PNG image (rendered using LaTeX and Matplotlib in a Django backend) to the clipboard. When downloaded, the image maintains its transparency as expected. However, when copied to the clipboard using JavaScript, the transparent background turns black.

Here's a simplified version of the JavaScript code responsible for copying the image:

document.getElementById('copyButton').addEventListener('click', function() {
    var imgElement = document.getElementById('renderedImage');
    if (imgElement) {
        var canvas = document.createElement('canvas');
        canvas.width = imgElement.naturalWidth;
        canvas.height = imgElement.naturalHeight;
        var ctx = canvas.getContext('2d');
        ctx.globalCompositeOperation = 'copy';
        ctx.drawImage(imgElement, 0, 0);
        canvas.toBlob(function(blob) {
            var clipboardItem = new ClipboardItem({'image/png': blob});
            navigator.clipboard.write([clipboardItem]);
        }, 'image/png');
    }
});

The issue seems to occur across multiple browsers. I suspect it might be related to how the canvas or the clipboard API handles the image data, particularly the transparency. However, on Firefox this actually appears to be unsupported completely.

Could anyone provide insights or solutions on how to maintain the transparency of the PNG image when copying it to the clipboard? I do not mind using a different method completely.

What I tried:
Checked and confirmed that the original image has transparency. Set globalCompositeOperation to 'copy' to preserve transparency. Tested in multiple browsers (issue persists across Chrome and Edge, while Firefox doesn't support ClipboardItem yet).

What I was expecting: When users copy the image to the clipboard, I expect the transparency to be preserved, just as it is when the image is downloaded.

Question: How can I ensure that the transparency of copied images is preserved when using the Clipboard API? Is there a specific method or workaround to prevent the transparent background from turning black in the clipboard?

Answer 1

SOLVED

This was not an issue with my "click-to-copy" function at all, but more an issue with the app I was pasting into. The app I was pasting into does not store the data for transparency. However, by copying and pasting into apps and programs that uphold transparency, the function works (on Chrome for instance).