This is something I get a lot of questions about on Youtube. People new to GIMP see tutorials where they need to "add an alpha channel" and are unclear about what it means. So I tried to explain it in this video. Maybe it's helpful to some newbies here too.

Excellent as usual, Jolie! Yes, this is vital information for any new GIMP user and a welcome addition to Gimp Chat tutorials. Thank you.

Thank You! It helped me to fully understand what an Alpha Channel Does.

One question, why wouldn't you want an Alpha Channel? To me it is always a bit of a pain to add one to everything, so would there be a way to have GIMP Add one Automaticly for you?

Not everyone wants transparency around an image. JPG images never have alpha channels and I personally wouldn't want one automatically added to all images. I like it the way it is now.

I guess so, I wonder if this could be an added Setting though. (default to not adding one, but could be changed so it would)

Understanding what an alpha-channel is is pretty much paramount to graphics design in general, not just on GIMP.

Some people are really annoyed (I mean frustrated to the point of pulling their hair out and giving up on GIMP) when it doesn't erase like in Paint. Once I even had a PM sparring match with someone willing to give up on GIMP because the checker board didn't want to go away.

I agree with you Willy. But in the cases above I give up and recommend they remove the alpha channel.

I suspect many beginner photoshop users don't know. They just double click (I think that is it?) on the bottom layer and then it works, when it didn't before. Wonder how many beginners know what they are doing...


p.s. Willy,
An image without an alpha channel is a smaller file (I'm 99% sure about this, not 100%). So it might have made a difference in the past.

You did an excellent job of it, I've seen some that get way too technical and it stupefies noobs, and I've seen some that just say 'alpha channel is the clear channel' which is very lame. Yours was just the right balance.

Not just lame, but totally false.

The best definition I can come up with is "the channel that controls the individual opacity of each pixel in a layer". Funnily enough, I've had to explain what "opacity" means to a few people...

We were all noobs once. Four years ago I could understand beginners just "giving up" on GIMP, mainly because there was a total lack of support for it. There were very few help sites and tutorials, and the elitism elsewhere was so thick even the most powerful saw in the universe couldn't cut through it.

Today, however, I can't even fathom someone being so exasperated that they "give up". There are tons of resources, help sites, chat forums, etc., readily available, with ready and willing people to help them.

Unfortunately, the alpha channel is referred to in ways an average person can't understand it. Once you manage to explain how an alpha channel works (like an overhead projector with clear plastic sheets) they "get it". We can waste time trying to be so perfectly correct in our descriptions, it's really a waste of time and pointless to the audience you're trying to reach.

Paint pictures with words people understand, not technical descriptions that baffles the majority.

Good job, Jolie!

Opacity is not a common used word, going from my experience of having to explain it to people who speak English natively.

The problem with getting technical is not getting technical, but that people often skips facts and basic knowledge, assuming their audience has the same knowledge as they do. Which obviously they don't or otherwise they wouldn't be looking for information on the matter.

Had the same thing happen to me the other day. I was looking up some info on some advanced computer thingy. Found the forum and had no idea what they were talking about. Found a thread for beginners.
The writer wrote something similar to this as opening post:

file > open > colors > desaturate (only more difficult terms for some other difficult program)
And a long list of numbers and values.

At the end of the post he asked if he forgot something. Another forum member said he did a great job, while I was screaming at the my computer screen:
"YOU FORGOT TO TELL US WHAT YOU ARE DOING!"

mahvin,
Maybe it helped that I don't know exactly into technical detail what an alpha channel is. I just tell people what they need to know in order to understand what you're doing.
To me, an alpha channel is a channel that makes transparency possible in an image. Is that correct?

In theory, yes. In reality its actually a mask channel. Which is why it gets so confusing when someone suggests using a mask in a tutorial, because sometimes they mean use an alpha channel. 32 bit programs have (4) 8 bit channels, 3 which are RGB and one alpha.

The alpha channel actually determines how colors (in an image object) will merge with other colors (on different layers), in a stack, based on the levels of opacity.

The bigger problem is that terminology differs across the globe, as you mention. Sometimes discussions get heated because of those differences. But as far as I am concerned, only photographers need to concern themselves with how channels are used effectively, because the average GIMP user's main functions for the alpha channel is to mask the object (without a background) in the image and to create transparent gifs and pngs.

I'm correcting the above statement to reflect what I truly meant, so I don't minimize or undermine the importance of channels to any GIMP user.

Quote:

"For a beginner, understanding channels should remain basic and understandable. Any artist who wishes to develop their craft, shouldn't limit themselves to the basics of anything GIMP or any other art platform has to offer. I strongly encourage beginners to expand their minds on all artistic enhancements, including channels. Channels are important to every artist, great and small, including photographers and animation artists."

A lot of new users don't have a clue what it means though. That's why I like hers, it's simple and gives a working example of how it works.

Jolie did a great job explaining it. I just wish more people like her were around to be as helpful, back when I was looking for help.

jolie,

Although I have been using Gimp for a while, I find your videos to be very helpful. With Gimp having so many features, I continue to find myself always learning new things about Gimp. I enjoy as well as learn from watching all of your Gimp video tutorials. Thank you.

My Story On Learning Transparency

For me, transparency and opacity with regards to image manipulation programs was a difficult thing to learn. I very well understood the terms transparent and opaque. However, in my mind, when I would erase an image, if it showed white, in my mind, that meant transparent. That may sound strange, but when I think of drawing something on a white piece of paper and then erasing it, I get back to a white piece of paper, not to a checkerboard.

Opaque meant I was seeing what was drawn. Transparency meant that I erased it and could no longer see the drawing. I didn't think of transparency as taking and cutting a hole in my paper so I could see what was behind the paper. And again, coming from an analog world, making that connection was hard for me.

I would have to say it took a long time before I really understood the checkerboard as a representation of transparency. Part of the issue that I also encountered difficulty with was layers. Before computers, my experience in the art world was limited, and layers were also a foreign concept. I remember reading the Gimp Savvy Book explanation of layers. Back then, I thought they were useless, since for me, art was about drawing everything on one layer of canvas or paper background. I could not imagine ever needing to use more than one layer, yet now multiple layers are indispensable for my pieces.

Putting all of these concepts into a meaningful perspective was very hard for me personally. That is always important to remember as well though. Because while I am a more experienced user now, it can be so easy to forget just how very difficult grasping these concepts can be. In fact, they were so difficult for me that I would install Gimp, get very frustrated, and delete it from my system. I repeated that process many times.

Although today, there are many helpful tutorials for new users to get them acquainted and accustomed to Gimp (or whatever image editor one wants to use), I imagine that many new users can still feel very inadequate and frustrated as well when they just don't get something that so many others seem to understand.

I learned very quickly once I entered the GNU/Linux world, to pay attention to those who offered me positive help and guidance and to avoid the RTFM crowd. Being someone who learns by doing, reading the manual usually only left me more confused and more frustrated. Having mentors to provide me with definite steps to take helped me tremendously. Only after I understood by doing, then the manual was a great supplement to build my knowledge after getting my feet wet. But I digress and my diatribe has gone on long enough. Now back to your regularly scheduled program.

Opacity is the inverse of transparency. That's what I tell people who don't know what opacity means




I think understanding channels is actually important to all kinds of artists, not just photographers and animators.

I think it's beneficial for an artist who creates digital art to know how the digital images are composed. It's good to know because you get a sort of "feel" of things, you understand the basic elements of which your image consists of... so you'll learn to manipulate them more effectively.

As for explaining the alpha channel, I'd start from the basics: your image consists of layers, and each layer consists of channels. Each channel defines the value of that channel for each pixel in that layer, and you have the R, G, B, A channels. When you look at a single pixel, it has R,G,B values which define the colour of the pixel, and Alpha value which defines the transparency/opacity of the pixel.

It gets more complicated when you consider layer modes, layer opacity and layer masks... Each of these further manipulates the alpha (and in case of layer modes, the other channels as well) of the layer. If your pixel's alpha is 80% and you set your layer opacity to 50%, then the pixel will be mixed with the stack as if it's alpha was 40% (80% * 50%). If you then add a layer mask that masks the pixel with a value of 50%, then the resulting pixel's alpha will be 20%.

It's like there's layers of methods to manipulate layers.

I hadn't considered explaining it in multiple languages, that does make it a lot more difficult. And thanks, having a conversation about technical stuff and 'advanced computer thingy' made my morning a lot lighter.

ccbarr, layers are one of those things that is easy once it clicks in your head, but hard to comprehend when it hasn't clicked yet.

Gms9810, at least Miss 'advanced computer thingy' got her wireless to work. (I'm just teasing you back)