How Can I Save an Image with Client-Side CSS Filters Applied Without a Backend?

Saving Images with CSS Filters Applied on the Client-Side

Issue:

How can you save an image after using CSS filters on the client-side without a backend?

Background:

Many developers encounter issues when saving an image with CSS filters applied on the client-side. Despite following a typical workflow of applying filters, converting to canvas, and saving with toDataURL, the result often lacks the intended effects.

Solution:

The key to resolving this problem lies in using the context object's filter property, which allows you to apply CSS filters directly to the bitmap. This property is not yet an official part of the web standard but has gained wider support in recent times.

Implementation:

Here's a concise implementation that incorporates the filter property:

// Check if the filter property exists
if (typeof ctx.filter !== "undefined") {
  // Apply the desired CSS filter
  ctx.filter = "sepia(0.8)";
  // Draw the image onto the canvas with the applied filter
  ctx.drawImage(this, 0, 0);
} else {
  // Fallback approach (not shown) for browsers without the filter property
}

Additional Context:

• CSS and DOM operate separately from canvas bitmaps. CSS filters affect elements (the viewing portals to bitmaps), not the bitmaps themselves.
• Manually applying filters to images requires pixel-level manipulation in the absence of the filter property.

• Resources for filter calculations:

  • Filter Effects Module Level 1
  • SVG Filters and Color Matrix

Example:

This example applies a sepia filter to an image on the canvas and extracts the result as an image:

var canvas = document.querySelector("canvas"),
    ctx = canvas.getContext("2d"),
    img = new Image();

img.crossOrigin = "";
img.onload = draw;
img.src = "//i.imgur.com/WblO1jx.jpg";

function draw() {
  canvas.width = this.width;
  canvas.height = this.height;

  if (typeof ctx.filter !== "undefined") {
    ctx.filter = "sepia(0.8)";
    ctx.drawImage(this, 0, 0);
  } else {
    ctx.drawImage(this, 0, 0);
    // TODO: Manually apply filter here.
  }

  document.querySelector("img").src = canvas.toDataURL();
}

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