How to Save Images with CSS Filters Applied from a Canvas?

Saving Images with CSS Filters from Canvas

Challenge

To save an image after applying CSS filters on the client-side, follow these steps:

1. Use CSS filters to enhance the image.
2. Convert the image to a canvas element.
3. Attempt to save the image with var data = myCanvas.toDataURL("image/png");.

However, this method often results in saving the image without the applied filters.

Understanding the Issue

CSS filters are applied to the element itself, but canvas elements represent bitmaps that are unaffected by CSS. Without the context's filter property, the only option is to manually apply the filters to the image pixels.

Solution

If the context's filter property is available (supported in most modern browsers), you can apply the filter directly:

var ctx = myCanvas.getContext('2d');

var filterVal = "grayscale("+ grayValue +"%)" + " " + "blur("+ blurValue +"px)" + " " + "brightness("+brightnessValue+"%)" + " " + "saturate(" + saturateValue +"%)" + " " + "contrast(" + contrastValue + "%)" + " " + "sepia(" + sepiaValue + "%)" ;
ctx.filter = filterVal;

If the filter property is not available, you need to manually implement the filter effects on the pixel level. Refer to the Filter Effects Module Level 1 and SVG Filters and Color Matrix for guidance.

Code Example

This example demonstrates how to apply a filter using the context's filter property:

// Create an image object
var img = new Image();
img.crossOrigin = "";
img.onload = draw;
img.src = "path/to/image.jpg";

function draw() {
  // Get the canvas and its context
  var canvas = document.querySelector("canvas"),
      ctx = canvas.getContext("2d");

  // Resize the canvas to match the image
  canvas.width = this.width;
  canvas.height = this.height;

  // Apply the filter using the `filter` property
  ctx.filter = "sepia(0.8)";

  // Draw the image onto the canvas
  ctx.drawImage(this, 0, 0);

  // Convert the canvas to a data URL
  var data = canvas.toDataURL("image/png");

  // Set the `src` attribute of an image element to the data URL
  document.querySelector("img").src = data;
}

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