View Full Version : Alpha Channel Question

03-16-2007, 12:33 PM
I have no doubt that this is an old topic. But I didn't really come across this topic in my search of the forums. Anyway, I was wondering why Lightwave treats alpha channels differently, and is a bit inconsistent with them. To be specific, practically every other graphics program on the market today treats alpha channels with white as opaque and black is transparent. Yet Lightwave is the inverse, (black is opaque, white is transparent) when dealing with texture maps and viewing them in OpenGL, however, in the renders it is the opposite, (white is opaque, black is transparent). Very interesting. To my knowledge, there is no preference setting for this, there are work arounds, but to me this seems like taking some unnecessary steps and can be easily fixed. What are your thoughts?

03-16-2007, 12:54 PM
As far as i know white is transparent when dealing with texture maps. Just that other software deals with this in different ways. Like 3dmax has Opacity instead of transparency. Therefore the more opaque you want something to be the whiter it needs to be. This is confusing after using LW, true, but i prefer the way LW does it.

In regards to Alpha channels, i think most software makes the solid things white, well 3dmax as far as i can remember anyway, correct me if im wrong!

03-16-2007, 01:34 PM
It's probably down to LW being a bit older than most packages now. In LW an alpha can be used to mask a texture, as if adding a decal. Also, in LW the 'opacity' channel is called the Transparency channel, so the whiter an image, the more transparent it is, like in the luminosity channel has white parts more luminous. Maya calls the opacity channel the Transparency channel, but uses the blacker parts to be more transparent sort of counter intuitively.

03-16-2007, 04:28 PM
True, but most compositing tools, or image editors treat the alpha as black is transparent. The same goes for 3D Max or Modo. Perhaps there just needs to be some sort of toggle either in the Image or Surface editor to just invert the alpha channel alone. This could prevent some possible rework.

03-16-2007, 06:04 PM
I'm not 100% sure what you mean!?

If i render in Modo, the solid parts are white and the transparent parts are black, the same happens in Lightwave! This works fine and always has done in compositing apps. Yeah, Transparency works the opposite of MAX and Maya, but this doesn't cause issues unless you want to convert a scene straight from MAX to LW and the maps will have to be inverted!

In this image taken from a quick render, the most transparent parts are black and the least bits are white! I'm pretty certain this is how most software works!?

Shout and scream if im completely wrong?

Basically, the way i see it is... white is on
black is off.
This is how Lightwave works with all its texture networks, and it works exactly the same as in other software packages, apart from Maya, which Dodgy mentions! The major difference and confusion is caused when 3dsMAX decides to use Opacity instead of Transparency. (Or you could say Lightwave causes the confusion, but i certainly find it easier to deal with transparency rather than opacity)

03-16-2007, 06:48 PM
I would say max and LW have it right where maya has it wrong. Maya calls it's channel transparency, but really it's opacity since white is more opaque in maya. In LW, white is more transparent thus it's a transparency channel. Max has white as opaque, hence opacity channel.

All output the correct alphas though.

03-16-2007, 07:28 PM
It's when you use a layer to mask the layer below it that LW has it backwards. Everything else is correct as I recall. In some cases an alpha is being applied as a b&w image, like in the transparency channel, so white = 100% transparent.

Considering what a ***** it is to layer anything in Max, I'll deal with the invert checkbox :)

03-17-2007, 03:29 AM
Considering what a ***** it is to layer anything in Max, I'll deal with the invert checkbox :)

I second that!!!! My boss has never seen anything else and loves the way MAXs texuring works! I'd rather chew a brick!

03-19-2007, 12:41 PM
It has been my experience, that when I bring any texture maps in from Photoshop or Particle Illusion or AE, where black is transparent white is opaque; I always have to go back and invert the alpha channels. For some reason, LW treats the alpha channel differently. It is my understanding that this is due to the way print houses used to mask off their graphics way way back in the day. They used to lay down a thin white sheet and cut their graphics around into it. Hence, the "white" would be masked and the "black" cuts in the sheet would be where the graphics would show up. However, I could be way off base here. Anyway, that is all well and good, but is stands to reason that there needs to be some sort of consistency in this area. At least some sort of toggle to invert just the alpha channel. This could save a lot of rework.

03-21-2007, 11:18 AM
in alpha channels white is allways opaque/ON and black is allways transparent/OFF. In material's transparancy channel(as in the channel that defines the amount of transparency) white is transparent (255,255,255 or MAX amount) and black is opaque (0,0,0 or zero amount of transparency). The alpha channel is not a transparency channel but an opacity channel, like Dodgy and lardbros says.
Maya has it wrong for the reasons Dodgy describe. I have never seen any graphics programs that use white as transparent in their ALPHA channels.

03-21-2007, 10:04 PM
I always have to go back and invert the alpha channels.
So the invert checkbox doesn't work for you since you just want the alpha inverted - can you describe how you're using the image, in which channels, any adjustments in the Image Editor? I've never had a problem like that.

The only channel that it makes sense, imho, to use the embedded alpha ( instead of using it as a b&w image ) is the color channel, and that works like all the other apps, as far as I can tell - this hand has a white alpha, not inverted, rendered on a blue polygon