Image Editor using CamanJS

Introduction

CamanJS is used for doing (ca)nvas (man)ipulation in JavaScript(JS). It is very easy to extend with new filters and plugins, and it comes with a wide array of image editing functionality, which continues to grow. It's completely library independent and works both in NodeJS and the browser.

Getting Started

Before we can start using different features of the library, we will have to include it in our project. This can be done either by downloading the library or linking directly to a CDN.

<script src="https://cdnjs.cloudflare.com/ajax/libs/camanjs/4.1.2/caman.full.min.js" integrity="sha512-JjFeUD2H//RHt+DjVf1BTuy1X5ZPtMl0svQ3RopX641DWoSilJ89LsFGq4Sw/6BSBfULqUW/CfnVopV5CfvRXA==" crossorigin="anonymous"></script>

Basics

There are two ways to use the library:

• Using the data-caman attribute with our image elements. This attribute can accept a combination of different CamanJS filters as its value.

  <img src="path/to/image.jpg"
    data-caman="brightness(10) contrast(30) sepia(60) saturation(-30)">

• Calling Caman() with the id of the canvas where we have rendered the image and different filters that we want to apply to the rendered image. This method assumes we already have a canvas element in the page, and we would like to load an image via URL into the canvas for editing with CamanJS. We can also give DOM objects instead of Strings if we prefer.

  Caman("#canvas-id", "path/to/image.jpg", function () {
    this.brightness(10);
    this.contrast(30);
    this.sepia(60);
    this.saturation(-30);
    this.render();
  });

In this article, we will be going the JavaScript way to build our image editor.

Upload Image

We need to provide users with a way to upload the images they want to edit so that we can render them on the canvas for further manipulation.

<input type="file" id="upload-file"></input>
<canvas id="canvas"></canvas>

const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");
const uploadFile = document.getElementById("upload-file");
let img = new Image();
let fileName = "";
// upload File
uploadFile.addEventListener("change", () => {
      const file = document.getElementById("upload-file").files[0];
      // init FileReader API
      const reader = new FileReader();
      if (file) {
        fileName = file.name;
        // read data as URL
        reader.readAsDataURL(file);
      }

      // add image to canvas
      reader.addEventListener(
        "load",
        () => {
          img = new Image();
          img.src = reader.result;
          img.onload = function () {
            canvas.width = img.width;
            canvas.height = img.height;
            ctx.drawImage(img, 0, 0, img.width, img.height);
            canvas.removeAttribute("data-caman-id");
          };
        },
        false
      );
});

Let's walk through the above code.

HTML snippet:

• <input> element with type="file": let the user choose one or more files from their device storage.
• <canvas> element: used to draw graphics on a web page via scripting.

JS snippet:

• The <canvas> element has a method called getContext(), used to obtain the rendering context and its drawing functions. This getContext() takes one parameter, the type of context. For 2D graphics, such as those covered by this article, we specify 2d to get a CanvasRenderingContext2D.

• The File API makes it possible to access a FileList containing File objects representing the files selected by the user. We used a classic DOM selector const file = document.getElementById("upload-file").files[0] to access the first selected file.

• The FileReader object lets web applications asynchronously read the contents of files stored on the user's computer. The object uses readAsDataURL method to read the contents of the specified File. Then, we added a listener for the load event which is fired when a read has completed successfully.

• The Image() constructor creates a new HTMLImageElement instance. It is functionally equivalent to document.createElement('img'). We set the src attribute to reader.result which is a string with a data: URL representing the file's data.

• Once the image has loaded successfully, we set the width and height of our <canvas> to be equal to the width and height of the image selected by the user. Finally, we draw the image on our <canvas> using drawImage(image,x,y) method.

Applying Filters

CamanJS has a wealth of built-in functionality from basic image filters to color conversion utility functions, and much more. All of these filters are included in the core library.

<div role="group">
    <button className="filter-btn brightness-add" type="button">+</button>
    <span>Brightness</span>
    <button className="filter-btn brightness-remove" type="button">-</button>
</div>
<div role="group">
    <button className="filter-btn contrast-add" type="button">+</button>
    <span>Contrast</span>
    <button className="filter-btn contrast-remove" type="button">-</button>
</div>
<!--preset filters-->
<button className="filter-btn vintage-add" type="button">
    Vintage
</button>
<button className="filter-btn nostalgia-add" type="button">
    Nostalgia
</button>

    document.addEventListener("click", (e) => {
      if (e.target.classList.contains("filter-btn")) {
        if (e.target.classList.contains("brightness-add")) {
          Caman("#canvas", img, function () {
            this.brightness(5).render();
          });
        } else if (e.target.classList.contains("brightness-remove")) {
          Caman("#canvas", img, function () {
            this.brightness(-5).render();
          });
        } else if (e.target.classList.contains("contrast-add")) {
          Caman("#canvas", img, function () {
            this.contrast(5).render();
          });
        } else if (e.target.classList.contains("contrast-remove")) {
          Caman("#canvas", img, function () {
            this.contrast(-5).render();
          });
        } else if (e.target.classList.contains("vintage-add")) {
          Caman("#canvas", img, function () {
            this.vintage().render();
          });
        } else if (e.target.classList.contains("nostalgia-add")) {
          Caman("#canvas", img, function () {
            this.nostalgia().render();
          });
        }
      }
    });

Let's walk through the above code.

HTML snippet:

• Filters like brightness and contrast have been given increase and decrease buttons.

• Preset filters like vintage and nostalgia do not require a parameter.

JS snippet:

• Instead of having event listeners for each filter buttons, we are listening to all the click events in the document. The target event property e.target returns the element that triggered the event.

• Then, we have a if statement checking if the element has a class filter-btn making sure that the event is triggered from one of our filter buttons. Inside it we have nested if-elseifstatements further checking which filter button fired the click event.

• Finally, we have Caman() to will apply the respective filters based on the button clicked.

Download Image

Once the users have made the changes, they should also be able to download the edited images.

<button id="download" type="button">
    Download
</button>

const downloadBtn = document.getElementById("download");
    if (downloadBtn) {
      downloadBtn.addEventListener("click", () => {
        // get extension
        const fileExtension = fileName.slice(-4);
        let newFilename;

        // check image type
        if (fileExtension === ".jpg" || fileExtension === ".png") {
          newFilename =
            fileName.substring(0, fileName.length - 4) + "-edited.jpg";
        }
        download(canvas, newFilename);
      });

      function download(canvas, filename) {
        // init event
        let e;
        // create link
        const link = document.createElement("a");
        link.download = filename;
        link.href = canvas.toDataURL("image/jpeg", 0.8);
        e = new MouseEvent("click");
        link.dispatchEvent(e);
      }
    }

Let's walk through the above code.

• The above code removes the file extension from the name of the image file selected by the user and replaces it with the suffix -edited.jpg. This name is then passed to the download function along with a reference to the canvas where we rendered and edited the image.

• The download function creates a link and sets its download attribute to filename. The href attribute is set to canvas.toDataURL(type, encoderOptions) which returns the data URI containing the representation of the image in the format specified by the type parameter and quality specified by the encoderOptions. After setting the value of these two attributes, we programmatically fire the click event for our newly created link. This event starts the download of the edited image.

The following demo shows the snippets in action:

Some filters & bigger images might take some time before you see their final outcome. In such cases, users might think that the filter is not working. We can make use of events to keep a track on the progress of a filter.

Conclusion

Now, we have a basic understanding on how to build an image editor with upload and download functionality. CamanJS offers many advanced and efficient image/canvas editing techniques. Be sure to read the documentation to explore the possibilities.