To get rid of the transparency-information in your image, just flatten the image:
Right click on your image, Image -> Flatten Image.
or,
From Layers panel right click on "Background" -> Flatten Image.
documented on: 2005.05.17
http://linuxguide.automatedshops.com/GimpGuide/layers_channels.html
Created November 29, 1997 Last updated: Novemver 4, 1998
Layers and channels seemed like two totally unrelated things to me, but what I've found out is that each layer can have channels disabled or enabled, depending on what you choose. If you don't know what I'm talking about, you'd better read on. :)
You'll probably need to use layers more than you'll want to use channels, but it's good to know what channels do anyway, so if you're bored and have nothing to do, you can disable the channels on your image…
Every other tutorial you read, you read about layers. You might already know what a layer is. In the GIMP, layers are like individual images within one, stacked on top of one another.
The mode that you choose for your layer affects how it "interacts" with the layer underneath. If you change the layer mode for the Background layer, for example, nothing will be affected. If you change the layer mode for the layer on top of "Background" however, the look will usually change.
By default, each new layer is put "on top" of the layer before it. This, however, can be changed. As with normal image operations, right-click, but this time click in the Layers dialog on the layer that you want to adjust. You'll see a menu pop up with things like Raise Layer, Lower Layer, Delete Layer… you get the idea.
There are many reasons you might want to use layers. One is that you can do as many things on a layer as you want, and if the results turn out crappy, you can delete the layer! Yes, undo is a great feature, but there are only so many levels of undo you can backtrack with (without driving your system's load average way up). Another reason is that you could be working on an image with a white background
The "control panel" for layers is the Layers dialog. This is also called the Layers and Channels dialog, but one section is specifically for layers. Here's what it looks like when the Layers and Channels dialog is set to let you manage your image's layers:
You can think of transparent layers as just that: something you can see right through. You can then add stuff on top of that transparent layer that isn't transparent. Think of the lowest layer as the kitchen counter, and a transparent layer as a piece of Saran Wrap; when you add stuff on top of the Saran Wrap, that part is covered by whatever you put in it, so you can't see through that portion of the plastic onto that section of the kitchen counter. You can see the parts that aren't covered by whatever you put on the Saran Wrap, however, so parts of that Saran Wrap "layer" still remain transparent.
When you clear a layer (Ctrl-K or right-click, Edit, Clear), it becomes transparent and with the stuff I've done, I couldn't use that layer anymore. What I usually had to do was either undo the Clear operation, or delete that layer and start over with a new one. However, you can't clear the Background layer just like that; if you try, whatever is set as your background color will fill the image. If you try to "clear" the image using Ctrl-X, you're deleting the background layer so that makes your image empty. At first it appeared to me that I had made the background layer transparent, but a check in the Layers dialog told me that there were no layers. I couldn't create any new layers after that and so that image was rendered useless. Of course, the mighty Undo (right-click, Edit, Undo; Ctrl-Z) feature of the GIMP is an option, taking you back to before you deleted the background layer.
Using channels won't prove useful most of the time, but if you've cropped an image and then started to work on it and the brush that you use appears to be the wrong color or doesn't seem to do anything at all, try making sure that everything (Red, Green, and Blue) in the Channels dialog is highlighted.
Right now I don't know exactly what channels are, but if you take a look at the Channels dialog with an image in RGB mode open, you can see what the image looks like without the Red channel by making the eye on the line marked "Red" disappear. Click on it. Click on it again. Can you see what happens to the image? It should have taken all the red out, and if your image was a plain white one, it should have turned green-blue.
The central control panel for channels is in the Layers and Channels dialog as well, only this time you click on the "Channels" tab after the layers dialog box pops up. Here's what it looks like:
Indexed images have only one channel; you can change that by making the image RGB (which is the mode you should be creating and editing images in anyway). With X pixmaps, sometimes a channel might be unhighlighted and therefore disabled. That brings up another point. For the best results, make sure all three channels (Red, Green, and Blue) are highlighted.
Again, whenever you're doing something and it doesn't do what it's supposed to, check to see if all the channels (Red, Green, and Blue) are highlighted. I remember that once I was working on an image and used Gaussian blur on the Background layer and it stayed the same; I ended up doing about three Gaussian Blurs with nothing happening until I checked the channels dialog while the highlighted, active layer was Background. I can't remember whether it was only one or all of the channels that weren't highlighted, but once all the channels were highlighted again, the Gaussian blur worked perfectly.
http://linuxguide.automatedshops.com/GimpGuide/anim_gif.html
Using layers is the key to creating animated GIFs with the GIMP. You'll have to create a new layer for every new frame of your GIF, so that means each layer is really a frame, and vice versa.
Add an Alpha-channel
Select the areas you want to make transparent
EDIT => CLEAR
http://aplawrence.com/Linux/crousegif.html
By Crouse USA Linux Users Group Web Site: http://www.usalug.org
Sometimes when working with an image you want to make a certain color transparent. When working with a gif file this would make a round circle look round on any color background. This is actually very simple once you do it once. Finding the information for this took me a while so I thought I would pass it on to anyone that was interested.
Open your image in the gimp.
Add an Alpha-channel to your image (using Layer > Transparency > Add Alpha Channel). For gimp 1.x, right click the image and go to LAYERS then ADD ALPHA CHANNEL. You won't notice anything happening, but don't be concerned. It basically adds a transparent layer at the bottom of your image so when we erase the colors…..it's shows the transparent layer. Which of course would show whatever was under it on the screen.
Right click on the image again and go to SELECT and then down to BY COLOR. A window that is all black opens up. Don't change any of the settings….just use the defaults for now.
Now click on the color in the image you want to be transparent. These colors will now show up outlined.
Right click on the image again and go to EDIT and then down to CLEAR. This should now erase the outlined color you just picked from the image and the "transparent gimp checkerbox" should show through. This is the Gimps way of showing you that section is now transparent.
Right click on the image and choose SAVE AS and make sure to save as a GIF file if you want the transparency to work on the web.
Most of this information was gleened from this webpage: http:// courses.washington.edu/englhtml/engl481/usegimp.html and of course my Gimp Bible and my Essential Gimp books.
Another fun feature that can be used while using the SELECT and BY COLOR ….. instead of hitting CLEAR you can FILL W BG COLOR or the other one FILL W FG COLOR ……….. this allows you to change the colors over the entire image instantly for the particular pixel color you choose to start with. Very fast and fun once you figure this out.
Tich:
Very useful. I wish I'd read it sooner! Also useful is the Fuzzy Selection tool, which can select a single contiguous area of one color.
Hemo:
Thought this would work just great, until I got to Step #2 and find that the option to 'Add Alpha Channel' is grayed out and can't select it. I saved as a PNG, did not save background color, then re-opened the file and was able to follow these instructions.
Malikive:
Just followed these steps using GIMP2.0 on a PNG…worked great! Thanks!
---August 12, 2004
I can see the alpha "checker-box" but then after I save it as a GIF and look at it in a browser I can't see my drop shadow anymore… why won't this darn thing work!?!?!
---August 12, 2004
Because you had the dropshadow included in the alpha mask.
---October 29, 2004
Thanks - I actually tried some stuff in the by color menue, but I couldn't figure out to click on the color on the image..
Somebody asked about the weird key for deleting:
I think it has something to do with the platform GIMP was designedn for first.
---November 15, 2004
Anon: instructions not clear enough and 'Add Alpha Channel" was ghosted out - pretty useless help page if you ask me
---December 14, 2004
Small change for Gimp 2.0, should be:
Right click the image and go to LAYERS, then TRANSPARENCY and ALPHA TO SELECTION.
The remainder is still accurate. Cheers, Colin.
---January 10, 2005
cenlatech:
first link in google to 'gimp transparency' and right on time, right on the money!!!
This is a Unix/Linux resource website. It contains technical articles about Unix, Linux and general computing related subjects, opinion, news, help files, how-to's, tutorials and more. We appreciate comments and article submissions.