I just come from TG, and noticed that there are people who have problems with transparancy and alpha channels: someone wrote that having an alpha channel is enough to get transparancy...???
A channel is a container for specific information concerning your file/image. Example: the Red Channel contains all information about what's red in your image. An Alpha Channel contains information that you, or someone else added to the file. When working for print (not your desktop printer!), you can add for example spot colours. These are colours made of separately mixed inks (most often Pantone) that broaden the narrow possibilities of CMYK, and are mostly used flat. . More on this another time.
You can also use Alpha Channels to save a selection. You know that a selection means that you want to do something with certain selected pixels and not with others that you did not select. The pixels that you did not select are masked. You can easily see this on the Tools palette when you click the Quickmask button. Masks are in fact greyscale images and therefore they can be stored in a container, the Alpha Channel container. So what you do is make a selection and then save that selection ( Select>Save). This way it is stored as a mask in the Alpha Channel. You can see this in the Channels Palette.
This way, when you save your file/image, you save the selection with it for later re-use. Handy, isn't it?
But what has this got to do with transparancy you may well ask.
A mask in an Alpha Channel in itself does nothing. When you activate it, you will only see what is masked and what not.
To get real and easy-go transparancy, you first turn your background into a layer by double clicking on Background in the layers Palette. Then you make a selection, indicating that you want to preserve these pixels and get rid of the others.
Next you click the little icon at the bottom of the Layers Palette that says " Add Layer Mask" and bingo!.
Fun thing is that you now also have an Alpha Channel in your Channels Palette, called LayerO Mask, or whatever yo named it. But this one does really make unselected portions transparant. But, because it's a layer, not a flattened image, you can't save in all formats. PSD is Photoshop's native one, and is the more interesting. You can also save as advanced tif. PS7 does this automatically, PS6 wants you to change its preferences.
(You can see what you do when you want to work on this mask by alt clicking clicking the mask icon. When you simply click, you see the small mask icon instead of the brush, indicating you work on the mask. Like this you can see what you do to the image itself.
Of course, you can soften your selection etc etc before you make a mask out of it, and you can paint in a mask to make a more perfect selection.)
Of course, for the web you need gif or png to get transparancy.
A channel is a container for specific information concerning your file/image. Example: the Red Channel contains all information about what's red in your image. An Alpha Channel contains information that you, or someone else added to the file. When working for print (not your desktop printer!), you can add for example spot colours. These are colours made of separately mixed inks (most often Pantone) that broaden the narrow possibilities of CMYK, and are mostly used flat. . More on this another time.
You can also use Alpha Channels to save a selection. You know that a selection means that you want to do something with certain selected pixels and not with others that you did not select. The pixels that you did not select are masked. You can easily see this on the Tools palette when you click the Quickmask button. Masks are in fact greyscale images and therefore they can be stored in a container, the Alpha Channel container. So what you do is make a selection and then save that selection ( Select>Save). This way it is stored as a mask in the Alpha Channel. You can see this in the Channels Palette.
This way, when you save your file/image, you save the selection with it for later re-use. Handy, isn't it?
But what has this got to do with transparancy you may well ask.
A mask in an Alpha Channel in itself does nothing. When you activate it, you will only see what is masked and what not.
To get real and easy-go transparancy, you first turn your background into a layer by double clicking on Background in the layers Palette. Then you make a selection, indicating that you want to preserve these pixels and get rid of the others.
Next you click the little icon at the bottom of the Layers Palette that says " Add Layer Mask" and bingo!.
Fun thing is that you now also have an Alpha Channel in your Channels Palette, called LayerO Mask, or whatever yo named it. But this one does really make unselected portions transparant. But, because it's a layer, not a flattened image, you can't save in all formats. PSD is Photoshop's native one, and is the more interesting. You can also save as advanced tif. PS7 does this automatically, PS6 wants you to change its preferences.
(You can see what you do when you want to work on this mask by alt clicking clicking the mask icon. When you simply click, you see the small mask icon instead of the brush, indicating you work on the mask. Like this you can see what you do to the image itself.
Of course, you can soften your selection etc etc before you make a mask out of it, and you can paint in a mask to make a more perfect selection.)
Of course, for the web you need gif or png to get transparancy.