HELP!! What IS THe transparent check box & why my render layer have no alpha?

[nrayyarn]

I got 3 question here. ( i using cycle)

1. What is the transparent check box in (render prop.-> films) for?
   I know in compositor it make the background transparent, but i mean what the reason for doing that?
   What problem it will solved or is it more effective in compositing?

2.If I make 2 render layer. and i want them share same background, what node i should add and
where to plugin or out?

3.I just made an test to combine two layer, but it didnt work as the tutorial shown in youtube.
*First image is basic setup for two render layer
*second layer is i put alpha over factor but it doesn’t work
*third image is i checked the alpha of the layer, it doesn’t have the alpha for the cube

What have i done wrong? where why there isnt any White part (alpha image) for the small cube but only the plane?

Thank you very much~ i am struggling in the way of learning blender so hard.
I need some help guys~ Thank you:)

Attachments

[Richard_Marklew]

1. What is the transparent check box in (render prop.-> films) for?
   I know in compositor it make the background transparent, but i mean what the reason for doing that?
   What problem it will solved or is it more effective in compositing?
   You can then layer different images on top of each other with the alpha over node instead of the mix node which will give the ghosting effect as the two images are mixed together

What have i done wrong? where why there isnt any White part (alpha image) for the small cube but only the plane?
The alpha is for the whole render, the plane is in the render so you have the alpha of the cube on top of the alpaha of the plane so you’ll only get the alpha of the plane. Of you don’t want the plane then don’t add it to that render layer.

What are you actually trying to do ?

[nrayyarn]

I just want to put this 3 object together in final compositing ~

Does that mean if i need to do so,
I need to separate EG. Plane and Cube A. in layer one, and Cube B in layer two. Then Composite with alpha over node? or mix node?

Thanks a lot for the answering~:) thanks

[Richard_Marklew]

A simple setup with separate floor and 2 cubes

Attachments

cubes.blend (104 KB)

[nrayyarn]

WOW! i got it now~ thanks a lot:))) THANKS!!! XD