Alpha Channel

[pilotwing]

Hello, can someone tell me whats alpha channel?, whats really used for and how it works?

Thanks

[Shylock]

A Alpha channel from what I learned the past few days is used to have a texture show up clear. By doing this you would have to create a Alpha channel and make them Black if you want them clear or using tones of grey to have them show up as tinted.

http://www.fsdeveloper.com/forum/search.php?searchid=724721 you will find a lot of talk in there about Alpha's. A lot better then what I can tell you.

[Tako_Kichi]

That's one use for them but there are others. For instance it can also be used to control which areas are shiny and which are 'flat' in the spec map texture.

[bzhyoyo]

in most paint programmes, an alpha channel is used to mask parts of a textures you want to work on: pure black is opaque, while pure white is transparent. So some sims (like cfs3) use dds format with an alpha channel in order to simulate transparency.
Oddly enough, some FS sims use the alpha channel, as said before, to define the shyniness of a part: pure black is matte, while pure white is blindingly shiny.

[johnh_049]

Oddly enough, some FS sims use the alpha channel, as said before, to define the shyniness of a part: pure black is matte, while pure white is blindingly shiny.

got that part backwards...at least for fs9, black is shiney and white is matte

[pilotwing]

Now i can try to get shiny textures whit the alpha channel
Thanks to all of you!

[OBIO]

Not only is the way in which the alpha channel used dictated by the individual sim, but also by how the aircraft MDL materials were created. In FS2004, for instance, the alpha channel is usually used to develop various levels of reflection...but there are some aircraft in which reflective materials were not used, and applying an alpha channel to those planes will result in the plane being transparent, with the degree of transparency depending on how dark the alpha channel is.

OBIO

[Milton Shupe]

To add a little more flavor to this confusion, in FS2004:

If the modeler identifies the texture with a _t suffix (per the SDK the _t was for transparency), then the alpha channel controlled the opaqueness/transparency level. However, if the modeler also exported with the "Has Light Map" option, then this required an _L suffixed texture with the same name to control the night lighting and to eliminate the transparency, optionally. The alpha channel of the _t controlled the degree of Glossiness. I also might add that the _L texture can also have an alpha to control whether the lighting was controlled by the landing lights (white) or the rest of the lights (black).

If under the same exporting options, the texture had no _t suffix, then the alpha channel controlled the glossiness. The modeler could also make this/these textured parts with a degree of opaqueness in the design program and still have glossiness controlled by the alpha.

So, you can see why painters and modelers alike become confused. Heck, I get confused still and have to go back to check. :icon_lol:

If the modeler turns off "has light maps", then other things happen, the best of which is chrome-like textures stay chrome at dusk and dawn. Strangely light maps still work (as in gauge back lighting in the VC) even with the option turned off. {shrug}

In both instances, dynamic shine (sun glare, not glossiness) is still controlled at the material level (usually texture level) in the model.

I always wanted to make a table to show the impact of all these options under the various settings but never got around to it.

BTW, in FS2002, the alphas had a bit different effect.

[pilotwing]

So two files control one thing?, i mean, in the case of the glow, one is the base texture (name.bmp) and there is another file (name_t.bmp) that controls the glow like the alpha channel? (meaning the same base texture but in grey scale where the black is more glow)

But maybe i need to read the FS2004 SDK before asking.

[Milton Shupe]

No, not exactly.

The FS2004 modeler assigns a texture name to a material.

The options in naming that texture dictate how the objects textured by that material and texture name will respond to alpha channels.

If the texture name is xxx.bmp:

1. It can have an alpha channel or not (can be 8-bit, DXTn, or 32-bit or any accepted FS format);

2. The material to which it is assigned has its own attributes like opacity (transparency), dynamic shine (sun glare).

3. If the xxx.bmp has an alpha channel and the material is set to 100% opacity, (the alpha channel defaults to white), the darker you make the alpha channel, the more glossy it gets. White = flat, Black = chrome, typical range for glossy is 190-230 RGB.


If the texture name is xxx_t.bmp: (_t allows alpha controlled transparency)

1. It can have an alpha channel or not (defaults to white) (can be 8-bit, DXTn, or 32-bit or any accepted FS format);

2. The material to which it is assigned has its own attributes like opacity (transparency), dynamic shine (sun glare). Usually the material for this xxx_t.bmp has a reduced opacity, like for glass or a prop.

3. If the xxx_t.bmp has an alpha channel and the material is set to 100% opacity, (the alpha channel defaults to white), the darker you make the alpha channel, the more transparent it gets. White = opaque, Black = invisible, typical range for glass is 30-50, and props maybe 10-15 RGB. However, the modeler can also set the material to 6% opacity and use a white alpha for a prop.

4. If the modeler exports the model with "Has Light Map", then any xxx_t.bmp that has a non-white alpha will show some transparency unless a xxx_L.bmp is provided (same root name with _L). The effect is without the _L bmp, FS believes the alpha channel is controlling transparency. So, you add an same-named xxx with the _L to correct that then the alpha channel controls glossiness.

5. When using an xxx_L.bmp, it too can have an alpha channel. If the alpha channel is white, the channel's effect will be seen when landing lights are on. If the alpha channel is pure black (0,0,0), the effect will be seen when any lights are other than the landing lights.


I hope I haven't screwed up this explanation and if so, hopefully someone will correct me.


So, some examples:

Fuselage:

fuselage.bmp (alpha channel if used controls glossiness; if not, it defaults to white)

No fuselage_L required since no fuselage_t.bmp is used


Glass:

Glass_t.bmp (alpha channel controls transparency or glossiness depending on if modeler used "Has Light Map" and if Glass_L.bmp is used)

Glass_L.bmp (modeler likely used "Has Light Map" and wants to have glossiness plus transparency in glass)


Blurred Prop:

propblurred.bmp (material opacity is set to near transparent in the model and no alpha is required)

propblurred_t.bmp (material transparency at 100 or less; transparency is controlled by the alpha channel-near black) No xxx_L required but if used, can further reduce opacity.