Render only alpha channel

[icarriger]

Hi, What if I just want to render the alpha chanel without the other channels (color and Zchannel), and i whant to do that as flat jpeg black and white images.

[joojaa]

jpeg supports no alpha! you could render out a black andf hite picture tough thats actualy the matte opacity.

Bu why n hell would you like jepag compression artifacts in your image?

[icarriger]

Hi Joojaa Thanks for the reply!!!

The thing is that I have an image secuence and I whant to render several versions on the secuence's alpha channel (manipulating the matte opacity) only for masking porpuses. I thought deselecting the color and z channel on the render globals window, but maya still renders all the channels.

If I can have the alpha channel secuence it does't matter if I save it on jpeg format beacause I can use it in after effects as stencil alpha and mask the same color image with diferents masks.

I don

[drblacksnake]

again. avoid using jpgs - they are being progresively damaged each time You save them.
To have only one chan, do comp in AFX - strip all the channels and revert A chan to let's say R.. and use it as lumaMask in later comps.
If diskspace bothers You, then render in compressed tiffs/tgas - sequence would be as compact as possible.

[jtk77]

I've been using maya .iffs , small size, great quality

[icarriger]

You're right, jpgs compromize the image cuality...I'll take your advance and try with tiff's and tga formats...on the other hand, despite of going to AfX, if I have a car rotating 360 degrees and i whant to render the body of the car separate from the wheels (in diferents layers) I'll have to change the matte opacity of the body's and wheel's shaders in order to define areas and avoid wheels not shoing properly or being displayed behind of the car.

so each time i render a diferent alpha, maya renders again the whole image and then the alpha...it takes too much time for the batch render . aditionaly...when I play the secuence on the fchek i cant save only the alpha secuence.

[drblacksnake]

apply any lambert or smth simple to all details, so it would render fast. problematic places could be only semi-transparent areas with reflections and highlights - leave there the original materials.

i am not sure it would decrease rendertimes if in renderGlobals turn off image rendering, besides it could be very nice.