Background color, alpha, and motion blur... bad combo??

[DaForce]

Is there a way i can have a spinning moblur'd box thats sitting on a matte plane and not have the environment color kinda of mixed in with the moblur.

Like when i save it as a PNG for example, and go into PS and put a red background, the object has an outline around the moblur that is the color of the environment/background color from max.

See examples.

The scene is just a vray plane with its properties set to be an alpha plane (-1.0, shadows and alpha ticked)
The box is spinning, and the environment color is blue (to exaggerate the problem).
The pictures were saved as PNG's, taken into photoshop and then a red background layer was added behind the image.
Note: I also tried TGA files and got the same result in PS.

No Motion Blur


Motion Blur


Is there a way of getting the moblur to not take on the color of the background in max, and just be properly transparent?

Also the shadows seem to be taking on the color of the background (obviously) is the only way to get the shadows on the matte/alpha plane to work is to have a background of a dark color (black or gray)??
Or am i doing something wrong.

[Austin]

As far as I know, no. .png's with an alpha (or any file type, really) have to designate the color and transparency for each pixel. Given that, you're always going to have the bg color mixed in. With that in mind, ideally your bg should match the color of your object as closely as possible so that when the alpha is applied your color stays true. Easier said than done on objects like the box, because of the white strip at the top. It might be easier to put in a bg that's similar or the same to what you're ultimately going to be compositing onto.

Maybe there's another file type out there that you can designate a matte color, or something similar?

[DaForce]

Yeah i was thinking it wasnt really possible at the moment.
I have already tried out the matching background to what it will be idea and that obviously works well. Its going to be a spinning box for a website that my friend is doing, and he has jey to decide what the background is to be. I can easily just render it out without moblur and then there is no problem. But i want the moblur just to add that extra touch of realism.

There should be a way to render with no BG, so it just used the objects color and then the transparency level. This would be very handy when using moblur, as it would result in no extra colors being added in.

So i also guess thats why the shadows on the alpha plane are also blue.

[jacksc02]

why not do the moblur post??

[DaForce]

I could, but wouldnt that destroy the PNG transparency???
Im saying that with no idea what so ever.. hahahah

[jacksc02]

well if you render out the velocity channel you can use that data to add the motion blur later. It wont kill the png transparency

[DaForce]

Sweet

Might give that a shot.
Would AE be able to handle it?

[jacksc02]

sure will

[DaForce]

Cool... might have a dabble

[Morbid Angel]

daforce, your mistake is rendering against red. What you should do is render moblurred object against black, then apply red bg later. Rule is always always render against black. Its the best color to premultiply with alpha

[DaForce]

Well i initaially render with blue... hence you can see the blue... the red was a background added in PS as a layer behind.

I tried black and i just get a black edge around the moblur.. which also looks shit.
But the shadows atleast look kinda correct then.

What would you sugegst would be the best way for me to do this?
Step by step maybe if you have time.

ALso, Chris, do you know how to do waht you suggested in AE using the velocity channel?
Any tips
Havnt tried yet but having a vague idea would help when i get around to trying it.

[Da_elf]

the thing is your choice of alpha. there is straight and there is pre-multiplied.

[DaForce]

Ahhh Elf, mate good advice at the right time.

So to get it working right, i had to render it out to a TGA with pre-multiplied UNTICKED. then with a little PS work i was able to save it out as a PNG with the proper transparency!!!!

See below.



Looks better??
Actually i tried doing this before, but i think i messed something up along the way.. or didnt use a black BG in max... but it works now

[Da_elf]

glad you got it working

[egz]

If you render to PNG premultiplied with a black BG you can remove the black color in photoshop by using the layer > matting > remove black matte command.