When someone watches tutorial videos on Photoshop or other editing softwares, one may notice that the editor often talks about the "alpha channel" and "masks". A novice, watching these videos, may mistakenly believe that these are some overly complex concepts only an expert could understand. When I started, personally, hearing those words fill me with trepidation, thinking I had stumbled upon a concept only an expert could grasp. The truth is, the idea behind the word is simple, and the tools are complex because of the plethora of options and settings.

The alpha channel and mask are both used to control the visibility of the image parts. for example you have a photo of a person with a background behind him. With the use of mask or an alpha channel, you can decide: what to show and what to hide. This is the only function that they serve, and the two tools are generally similar, with the primary difference being the context in which they are applied. Once you understand the two tools, you will be able to follow most photo editing tutorials with ease and be able to understand the purpose of each step.

In this article, you will learn the difference between the alpha channel and mask in photo editing. The terms will be explained in simple words so that you can easily understand the concepts and be able to apply the tools in your own photo editing projects.

What Is an Alpha Channel, Really?

When I first heard the term “Alpha Channel,” I thought it sounded like some type of extra layer for the image, and it kind of is, but it’s more of a hidden guideline attached to the image. Think about it as something like having a picture except there is some hidden paper attached to it, on that paper there is some hidden writing that tells the computer exactly what to do. The hidden writing guides the Hidden note software to reveal, or to hide certain parts of the picture. It works in a similar fashion to when a teacher is grading papers and they use a red pen to mark up the paper, showing what is right and wrong.

Think of it like you have a thin transparent sheet with some holes into it. You can see the image underneath through the holes, but the image is obscured wherever the sheet itself is present. The alpha channel works in exactly the same way; the only difference is that the paper sheet is physical and alpha channel is digital.

It instructs the program on which pixels to make transparent. Unlike simply being able to hide or reveal an image, an alpha channel can also represent varying levels of transparency, such as with the fade from opaque to transparent. This allows for more complex images, such as hair or smoke, to be properly represented.

The reason why this is useful is because many editing functions require this sort of information. Background erasing, PNG transparency, and photo composites all use this sort of information.

You don’t have to remember the bits about transparency, pixels, or whatever else. Just recall that an alpha channel is an instruction set telling an image what to reveal and conceal.

Layer Masks vs Alpha Channels: Clearing the Confusion

When I first learned photo editing, I believed that layer masks and alpha channels were the same thing. The reason was that their functions appeared quite similar. First of all, both tools are used to control the visibility of the image parts. Secondly, both layer masks and alpha channels are subject to various operations, such as deleting, moving, duplicating, and more. In other words, the behavior of both seems quite similar within the software.

However, there is a particular contrast between these two concepts, considering that one is a part of another. To put it shortly, a mask is a part of a layer, while an alpha channel is a part of the layer mask.

To understand the difference between alpha channels and masks, you need to remember when and where you need them. When I want to edit some of the image parts by hiding some of the areas in it, I use a layer mask .For example, for making changes in the background or for concealing it, for these purposes, I use the mask. It allows me not to delete the image but to hide it with the help of this tool. Plus, I can use the mask for the entire image or only for one of its objects. Consequently, by masking half of the image on my computer, I will be able to see it again if I want. My image will be deleted, but it will be masked.

The function of the alpha channel is not editing. Its main purpose is to save information. For example, several days ago, you might have picked out some really frizzy hair. Now, you want to be able to use this selection in the future as well, so you will save it to an alpha channel. Alpha channels is used to storage complex subject selections like hair, fur, smoke and tree branches because it is difficult to select these items all at once.

Moreover, to clarify the difference between alpha channels and layer masks further, it might be useful to provide an example.

Let’s say there is an image with a lot of details that need editing. In this case, using of layer mask is relevant to edit and change image’s transparency to receive the desired result. As for the image with several specific objects (for example, hair or fur) that need to stay the same after image editing, in this case, the alpha channel will be used. As mentioned earlier, alpha channels are great for storing complex selections. Therefore, in most complex projects, one cannot use layer masks or alpha channels alone because of their different purposes. However, the provided examples illustrate the main differences between the two tools.

Why Black, White, and Gray Matter in Masking

If you learn Photoshop masks, there is an absolute beginner rule for this, following which you will learn masks easily; the best thing about it is that you will have to memorize only several colors.

White means the image remains visible.

Black means the image becomes hidden.

Gray means the image becomes partially visible or semi-transparent.

If you understand the principles behind these three colors, you have grasped half the idea of the mask, and mastered another half of more advanced techniques. I see the mask as a special black and white map. Photoshop keeps white areas visible, hides black areas, and keeps gray areas partially visible.

Let's understand this with another example to make it easier to grasp. Suppose I have a picture of a person and I want to remove the background. I will turn the background black so that it is hidden. Second, I will ensure that the person’s body is white enough so that it remains visible on the black background. Further, I will make the person’s hair gray as the hair usually has delicate outlines. When I was doing hair selection, I discovered that it is better to leave hair in gray instead of making it black or white. The reason is simple: using gray color allows one to observe delicate detail in hair texture, unlike black and white.

By the way, most of the interesting Photoshop effects are based on the same principle. The only difference is that, in each particular case, you have to use other techniques to achieve the desired result. The process was complicated, but there were some simple rules to follow. This is how I worked with Photoshop.

Why Masks Are Non-Destructive (And Why That's Great)

The major benefits of using masks is that they are non-destructive. This means that you do not destroy the original image while you make changes to it; you can edit the image and still have the original one. If you try to delete the background, not using a mask, the particular part you deleted becomes missing on the image. If you deleted too much and you need a part of the background you cannot get back, it would be a hassle; you would either have to undo your work or find the original image. On the other hand if you use masks it does not delete part of your image. It just covers it up so you can make the changes you want to quickly and easily.

By accident if you make a wrong move, it can be easily retrieved, since the mask does not delete, but only hides the desired elements. Thus, the work is much more safe, especially for beginners, as they can always return and fix the mistake without changing the entire image. For this reason, masks are used in photo editing software to make the process of editing photos less intimidating and more accessible.

How This Connects to Background Removal

At this point, you may be asking yourself what is the connection between alpha channels, masks, and removing a background. If this is the case, you are in the right place, as the following is an explanation of this connection.

First of all, recall that with the help of masks and alpha channels, you can separate the foreground and the background. This means that each element of the image is given its place, and the removal of any element becomes possible. In other words, if you want to delete the background, this can be done with the help of these elements since they provide control over the visibility of each image part.

Consequently, if you delete the background in an image using a background eraser, you will see all the features described above. A white color indicates which elements of the image will remain visible, and black color indicates which elements will be deleted. Thus, with the help of masking, you can edit the image with high precision and detail. The gray color is used to indicate areas of the image that require special attention.

In turn, this knowledge is useful to you because it allows you to understand the essence of the mentioned above concepts, as well as their importance and benefits. Moreover, the described above knowledge allows you to explain why this or that problem occurs and find a solution for it. Finally, the understanding of these terms provides insight into the functioning of various photo editing software.

Conclusion

In my opinion, the terms “alpha channels” and “masks” are something very mystical and profound. At the same time, the more often I started to use these terms, and the more often I used Photoshop, the more frequently I realized that it is all really simple. The simplest thing about masks is that they are a way of telling Photoshop what to show and what to hide. It means that we can control the visibility of the image. Using of alpha channels gives us an opportunity to store that visibility. We can say that they contain information about the visible and invisible parts of the picture.

Masks are really great inventions because they allow making selections non-destructive. It means that if we messed something up, we still have a chance to fix it. Using “white as” and “black as” gives us an opportunity to achieve a nice look of the image. It is particularly important if there are some hairs or other fine details in the image. At last, everything looks nice, and the initial image itself remains untouched.

So, there’s nothing to fear from alpha channels or masks, really. Learning their basic principles makes the idea of photo editing significantly less intimidating.

For those who would rather not bother with any of the theoretical basis of photo editing, however, tools like BG Erasers do most of the heavy lifting for you. They allow you to edit photos with masks and alpha channels as simply as using a convenient built-in tool.