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Creating an Image Editor Using CamanJS: Layers, Blend Modes, and Events

This post is part of a series called Creating an Image Editor Using CamanJS.
Creating an Image Editor Using CamanJS: Applying Basic Filters

In the previous tutorial, you learned how to create an image editor using CamanJS which can apply basic filters like contrast, brightness, and noise to an image. CamanJS also has some other built-in filters like Nostalgia, Pinhole, Sunrise, etc., which we applied directly to the image.

In this tutorial, we will cover some more advanced features of the library like Layers, Blend Modes, and Events.

Layers in CamanJS

In the first tutorial, we only worked with a single layer which contained our image. All the filters that we applied only manipulated that main layer. CamanJS allows you to create multiple layers to enable you to edit your images in a more sophisticated manner. You can create nested layers, but they will always be applied on their parent layer like a stack.

Whenever you create a new layer and apply it on the parent layer, the default blend mode used will be normal. You can create a new layer on the canvas using the newLayer() method. When you create a new layer, you can also pass a callback function which will be useful if you intend to manipulate layer.

This function can be used for a lot of tasks like setting the blend mode for the new layer using the setBlendingMode() method. Similarly, you can control the opacity of the new layer using the opacity() method.

Any new layer that you create can be filled with a solid color using the fillColor() method. You can also copy the contents of the parent layer to the new layer using the copyParent() method. All the filters that we learned about in the previous tutorial can also be applied on the new layer that we are creating. For example, you can increase the brightness of the newly created layer by using this.filter.brightness(10).

Instead of copying the parent or filling the layer with a solid color, you also have the option to load any other image in the layer and overlay it on the parent. Just like the main image, you will be able to apply different filters to the overlaid image as well.

In the following code snippet, we have attached a click event handler to three buttons which will fill the new layer with a solid color, the parent layer, and an overlay image respectively.

Blend Modes in CamanJS

In the previous section, we kept the opacity of any new layer that we added to the canvas below 100. This was done because the new layer would otherwise hide the old layer completely. When you place one layer over another, CamanJS allows you to specify a blend mode which determines the final outcome after the placement. The blend mode is set to normal by default.

This means that any new layer that you add on the canvas will make the layer below it invisible. The library has ten blend modes in total. These are normal, multiply, screen, overlay, difference, addition, exclusion, softLight, exclusion, and darken.

As I mentioned earlier, the normal blend mode sets the final color to be equal to the color of the new layer. The multiply blend mode determines the final color of a pixel by multiplying the individual channels together and then dividing the result by 255. The difference and addition blend modes work in a similar manner, but they subtract and add the channels.

The darken blend mode sets the final color of a pixel to be equal to the lowest value of individual color channels. The lighten blend mode sets the final color of a pixel to be equal to the highest value of individual color channels. The exclusion blend mode is somewhat similar to difference, but it sets the contrast to a lower value. In the case of the screen blend mode, the final color is obtained by inverting the colors of each layer, multiplying them, and then again inverting the result.

The overlay blend mode acts like multiply if the bottom color is darker, and it acts like screen if the bottom color is lighter.

If you want the colors in different layers to interact in a different manner, CamanJS also lets you define your own blend modes. We will cover this in the next tutorial of the series.

Here is the JavaScript code to apply different blend modes on an image:

In the above code snippet, we get the Hex color value from an input field. This color is then applied on the new layer. You can write the code to apply other blend modes in a similar manner.

Try to specify a color of your choice in the input field, and then apply any of the blend modes by clicking on the respective button. I have applied the blend modes on a solid color in the example, but you can also apply them on an overlaid image from the previous section.

Events in CamanJS

If you uploaded any large image in either the demo of the first tutorial or the second tutorial, you might have noticed that the result of any applied filter or blend mode became evident after a long time.

Large images have a lot of pixels, and calculating the final value of different channels for each pixel after applying a specific blend mode can be very time-consuming. For example, when applying the multiply blend mode on an image with dimensions 1920*1080, the device will have to perform multiplication and division over 6 million times.

In such cases, you can use events to give users some indication about the progress of a filter or blend mode. CamanJS has five different events which can be used to execute specific callback functions at different stages. These five events are processStart, processComplete, renderFinished, blockStarted, and blockFinished.

The processStart and processComplete events are triggered after a single filter starts or finishes its rendering process. When all the filters that you specified have been applied on an image, the library fires the renderFinished event.

CamanJS divides large images into blocks before starting to manipulate them. The blockStarted and blockFinished events are fired after individual blocks of the image have been processed by the library.

In our example, we will only be using the processStart and renderFinished events to inform users about the progress of our image editing operation.

With the processStart and processFinish events, you get access to the name of the process currently operating on the image. The blockStarted and blockFinished events, on the other hand, give you access to information like the total number of blocks, the current block being processed, and the number of finished blocks.

Try clicking on any button in the demo below, and you will see the name of the process currently manipulating the image in the area below the canvas.

Final Thoughts

The first tutorial of the series showed you how to create a basic image editor with built-in filters from the CamanJS library. This tutorial showed you how to work with more than one layer and apply different filters and blend modes to each layer individually.

Since the image editing process can take a while for large images, we also learned how to indicate to users that the image editor is actually processing the image and not sitting idle.

In the next and final tutorial of the series, you will learn how to create your own blend modes and filters in CamanJS. If you have any questions related to this tutorial, feel free to let me know in the comments.