How to Save Images with CSS Filters Applied Using Client-Side Canvas?

How to Save Image from Canvas with CSS Filters

Introduction

Applying CSS filters to images on the client-side can enhance their visual appeal. However, directly saving these filtered images can be challenging without using a server-side backend.

Step-by-Step Process

1. Create the Canvas Context:

• Create a canvas element myCanvas and its 2D rendering context ctx.

2. Draw the Original Image:

• Draw the original image (image1) onto the canvas using ctx.drawImage().

3. Apply CSS Filters:

• Calculate and concatenate CSS filters based on user input or preferences.
• Set the filter to the canvas using $('#myCanvas').css('filter', filterVal) to apply the combined CSS filters.

4. Obtain the Filtered Image Data:

• Use myCanvas.toDataURL("image/png") to convert the canvas bitmap into a Data URL representing the filtered image.

5. Save or Display the Filtered Image:

• Store the Data URL in local storage or use document.location.href = data to display the filtered image in a new tab or window.

Common Issues and Solutions

Issue: Image is saved without any filters.

Solution: Check for the existence of ctx.filter property. If supported, apply CSS filter directly to the context. If not available, provide a fallback to manually apply filters.

Browser Compatibility

The ctx.filter property is not part of the official HTML Canvas 2D specification but is available in Firefox and other supporting browsers. Some filters may also not be supported across all browsers. Refer to the latest browser compatibility documentation for details.

Example

The following code snippet demonstrates the process:

var canvas = document.getElementById("myCanvas"),
    ctx = canvas.getContext("2d"),
    img = document.getElementById("image1");

ctx.drawImage(img, 0, 0, canvas.width, canvas.height);

var filterVal = "grayscale(0.5) blur(5px) brightness(110%)";

if (typeof ctx.filter !== "undefined") {
  ctx.filter = filterVal;
  ctx.drawImage(img, 0, 0);
} else {
  // TODO: Manually apply filters
}

var data = canvas.toDataURL("image/png");
localStorage.setItem("filteredImage", data);

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