Alpha Channels - Man, I'm thick or something

[SandmanNinja]

Hi...

 

I've searched here and I've Googled it as well, but I just don't get how to use Alpha Channels.

 

I've rendered a scene in 3DS and saved it as a TGA.

 

Step 1 done.

 

I open it in Photoshop CS3, click on Channels, and see RGB and R G B & Alpha. If I click alpha, I get the black and white mask.

 

What I don't get next is... and all the info I find talks about how to GET the alpha channel... How do you actually take a photograph of a scene that you want to use out your window and get the alpha channel to snip out the bits that fill in the main room?

 

Any pointers would be greatly appreciated.

[manta]

well if I'm following you correctly, you want a background for outside the window,

just render either without the glass in the window, or set the material to use the alpha, bring it into PS, and put any picture in the layer under the render, it should show through the windows now...

[SandmanNinja]

Got it!!

 

Thanks heaps!

 

[Bwana Kahawa]

You can also hold down the Apple key on a mac (Ctrl on PC?) and click on the channel's thumbnail to turn the alpha channel into a selection.

[SandmanNinja]

Thanks for that.

[brianzajac]

You can also hold down the Apple key on a mac (Ctrl on PC?) and click on the channel's thumbnail to turn the alpha channel into a selection.

 

 

If you look at the top of the sky area, it's a little too sharp. To help blur this, make a selection like Bwana suggested. Then you should feather the selection. Go to Select --> Feather and use a small number for your radius (1 or 2 might work). This will turn your selection a little less sharp. Layer this on top of your other "sharper" layer. Then remove any other areas that look fuzzy. It should look a little better. Finally, in the layers tab (next to channels & paths), experiment with the blending options. It's the drop-down underneath the tab name (1st name is "normal").

 

Hope that helps too...

[Sketchrender]

Take your tga into photoshop.

go to select, load selection , click alpha and thats how you select the alpha.

Once you have previously turned it on in the layers.

 

phil

[Ky Lane]

You need one of those special "Do what I'm thinking; not what I'm telling you to" buttons on your keyboard.

[SandmanNinja]

You need one of those special "Do what I'm thinking; not what I'm telling you to" buttons on your keyboard.

 

hehehehe

 

Thanks everyone!

[WAcky]

Now think about how powerful masks can be.

 

When i render out now i make masks of every major object which makes colour correction soooo much more accurate and quicker.

[SandmanNinja]

Never thought of that, but you're right. Guess an extreme case would be to render out an alpha layer for almost every object, combine them as individual layers in photoshop, and fine tune away!

 

bloody brilliant.

[WAcky]

not an alpha layer but a matte pass. Get a material thats 100% white and 100% black. then apply black to everything and white to the specific object. Then you can use them with adjustment layers in photoshop.

[jkletzien]

umm, yeah you can do that, or...

 

http://cebas.com/products/products.php?UD=10-7888-35-788&PID=38

[SandmanNinja]

Hey Jon,

 

Thanks for the link.

 

Yeah, it's a great product, but I was hoping for a demo version for Max 2009 Design before buying it.

 

I'd like to see how it would affect my workflow, if I need to fractor in extra time for each render, etc.

 

Admittedly, it's "only" AU$150, but I've learned to never use the words "only" and "money" in the same sentence.

[Nic H]

A useful script I use ALOT for making mattes for stills and animations is somethign called 'quickmask' on scriptspot.

 

http://www.scriptspot.com/3ds-max/quick-mask-object

 

you select your object/objects and press the button and it makes a black and white image of your selected objects in white. you can then use this as a selection channel without having to change around materials etc.

[Billabong]

Very nice Script Nic, thank you

[SandmanNinja]

Saved to my HD and booked marked.

 

Thanks heaps.

[mattclinch]

also, try..

 

http://www.scriptspot.com/3ds-max/l-pass-manager

and

http://www.scriptspot.com/3ds-max/rendermask

 

great stuff to speed up that tedious bit of post prep.

[Nic H]

oops render mask is actually the one I use not quickmask.

rendermask does image sequences.

[Tommy Burns]

A good tip that I use is render out the scene with MAT Overide material set to none. This gives you your scene in all different colours which in turn can be changed to a mask using the magic wand very easily.

I also use the shader subset of scene for MR, great for glass.

Hope this is of some help

[mattclinch]

A good tip that I use is render out the scene with MAT Overide material set to none. This gives you your scene in all different colours which in turn can be changed to a mask using the magic wand very easily.

I also use the shader subset of scene for MR, great for glass.

Hope this is of some help

 

i find this gives really bad AA to your masks and therefore makes them quite innaccurate. if you shift the colour of an object or its brightness to far with this method do you not get haloing and strange edging issues?

 

i always find black/white mattes much easier as you can copy them directly into a PS channel.

[Tommy Burns]

Yes maybe so but I was just trying to show an easy way of selecting and creating masks and yes you might have to do a bit of work on your selection afterwards or the way you select in the first place. You can always use the colour selector on this which is probably better as you can do a lot more with the selection fuzziness, feathering etc.

[Nic H]

hey tommy if you are after clean multiple masks you should try the multimatte vray render element. it does R, G, B channels based on object or mat id. very useful.

 

the only slightly annoying thing is each element can only have 3 channels (rgb) so if you want more than 3 masks you need to add another element.

[Tommy Burns]

Cheers for that Nic but I'm afraid i'm an MR user there is prabably something similar in MR anyone know what it is?

[Nic H]

whoops sorry didnt read that.

i recommend changing to vray