Alpha is Luminance

[hexxi24]

could some please explain to me what is the Alpha? and what is Luminance? and Alpha is Luminance.?
because i am now learn the maya textures someitmes i always see Ahpla is Luminace option in the 2d and 3d texture common attribute and even in the layer texture also has this function , but when i use ipr to test this option , nomatter if this option is been checked or not checked the result always
the same maybe i still could not get them very understand , so
if someonce can give me a good example and the clear explaination, i will really appreciate.
thank you very much

[gmask]

What Alpha and Luminance share in common is that they are both grayscale. You can use the luminance of an image as an alpha channel if that serves your purpose like compositing smoke. Luminance is the value of brightness of any given pixel has in an RGB image. The alpha which is stored as a seperate channel apart from the RGB. Typically when somebody says it's a 32 bit image they mean an image that has RGB channels and alpha. That's 8bits per channel. Most RGB image formats are stored using a total of 24bits.

However these days there are RGB images where the individual channels are greater than 8bits. There are now 16bit and 32bit image formats that store that many bits per channel.

The alpha is Luminance option effects how the alpha channel is created for a rendered image. I played around with this a little bit and couldn't really get it to work. Then I thought maybe in some cases where you have a file image that does not have an alpha channel that this would force operations that require it to use the luminance as the alpha but that doesn't seem to work either.

g

[provide]

In reply to:
could some please explain to me what is the Alpha? and what is Luminance? and Alpha is Luminance.?
because i am now learn the maya textures someitmes i always see Ahpla is Luminace option in the 2d and 3d texture common attribute and even in the layer texture also has this function , but when i use ipr to test this option , nomatter if this option is been checked or not checked the result always
the same maybe i still could not get them very understand , so
if someonce can give me a good example and the clear explaination, i will really appreciate.
thank you very much

1- In 2D file texture node, Out Alpha = Alpha Channel ( Mask ) of Image.
TGA, IFF and other formats supports 24 RGB + 8 Alpha = 32 bit per pixel.

2- In other texture nodes, Out Alpha = Grayscale of the resulting color.

3- In both cases when "Alpha Is Luminance = ON"
Out Alpha = Luminance of the resulting color = ( 0.30*Red ) + ( 0.59*Green ) + ( 0.11*Blue ).

Martin
www.geocities.com/provide3d

[gmask]

3- In both cases when "Alpha Is Luminance = ON"
Out Alpha = Luminance of the resulting color = ( 0.30*Red ) + ( 0.59*Green ) + ( 0.11*Blue ).

Let's say you have an image file with no alpha and you connect it to the color channel and the alpha out to the transparency. Wether or not Alpha is Luminance is checked the luminance is sent out the alpha.

But if you have an image with an alpha channel and you want to override the embedded alpha on the alpha output then this checkbox replaces the embedded alpha with the images luminace.

g