Dumb Question: What is a Halo?

I keep hearing about halo, about how one should blur the edges and opacity, etc. But now that I've got the alpha channel thing down, I don't notice anything odd when make something (no white borders or anything) so what is this halo?

depending what program you used - the way you created the alpha channel and the resolution or even the origional to .tga conversion can sumtimes create a halo (sometimes also known as an aura)

this halo is a surrounding of the item with an unintentional outline, this is sumtimes noticeable in tv shows (especially some weather reports) where the person seems to be surrounded by a green outline (due to them using a green background)- and is not blending totally into the background and can sumtimes be very unslightly

better explination for star wars buffs...
those of you that has seen the special on how the ice planet tiefighter/land battle scene in star wars can see what is ment by the halo effect and how they combatted it by making the above image of the pilots in the tiefighters slightly transparent, next time you watch the movie (the orig not the re-visulisation) look to see the chicken walkers and other land veihcles actually visable through the 'metal' parts of the fighters and even the pilots themselves - as these are speedy scenes they decided this was enough to combat the problem

sometimes this effect can be created by getting rid of the background (the area you want to be transparent) by first colouring over it in a single colour - then choosing 'select colour -> alpha to selection' (as in the green rooms of filmsand tv shows) u can make this less visable by making the edges of the subject fading out or the entire subject slighlty trans

im not an expert on the subjebt and other people who use photoshop or gimp may be able to show u a better way

kornation
to much time on hands at the mo

In terms of looking for ways to combat it hunt for posts by Chosen Few with the words alpha channel in them.

Halos occur quite often. I happened to be near a television showing the build-up to some rugby match this afternoon. They had nice 'cut out' pictures of the players on a fairly plain blue background. Without wishing to comment on how sad I am, the main thing I noticed was the lovely halo around each of the player's heads. Avoiding halos can be tricky, even for big professional companies.

It's also a nice illustration of the origin of the name, on one of them there was this silver glow around his head, just like pictures of angels and saints.

this is a trick i use bouncing back and forth from the gimp to psp6.
it could work for clothing if done with care.

In the gimp: save my picture (with alpha) as a png file with no compression, do not save color info from transparent pixels, and do not save background color.
This alone can reduce the halo 25-50%.

Load the picture in paint shop pro 6 (i like it but ive got pshop too), psp6 is funky with how it handles alpha, the loaded picture should contain the cutout like normal, but the outside (transparency) is black. The ezest thing, but not the only way, is to paint over your nontransparent area to make the whole picture black (transparent?, dont worry)
save the picture close psp.

Back in the gimp: load the picture, and hey! the image retained its transparency, and the white fuzzy halo, has been reduced to a fine black penline, save as tga, upload

im shure theres ways to acheive the same thing without having a library of programs, but this "unique" example with these 2 programs works magic.