Ture Transparency and AO for compositing

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Old 05 May 2013   #1
Ture Transparency and AO for compositing


I need to create some product shots for a website that need to be saved as .PNG so I can change the background color and don't have problems. But I'm having some trouble creating the Ambient Occlusion and Shadow pass from Cinema...

I set up a multipass render with passes for Shadows, AO and object buffers for the blocks.

What I get from Cinema in the Shadow and AO passes are black and white renderings that are multiplied over the other layers. But what I need is a true transparent pass. I'm attaching an image to explain a little better.

I was able in Photoshop (using channels) to recreate what i want but it's going to be tedious to create all the graphics this way. Is there a better way to set up my pass so I get true transparency?

Any suggestions?

Full size image here

Fernando J. Velarde

Old 05 May 2013   #2
A quick (and perhaps dirty solution, though I have not experienced problems with it) is to open the AO pass in photoshop, select by color range, select the white and hit delete. Then drag the bottom slider to get the layer to be 100% black. Make it an actionscript and then it takes 0.000secs for it to do the same to other images.

But yer probably looking for Shadow Catcher and AO Catcher (I think AO Catcher does the same, could be wrong though).

Old 05 May 2013   #3
Shot in the dark here,
but ages ago there was a free photoshop plugin called 'eliminate white',
which worked very well to swap white for transparency.
(It's old and I have no idea if it's still around or even works with current versions of photoshop)

Personally I would not go for the colour range / delete workaround, it's not very accurate.
(unless I missed something)

Old 05 May 2013   #4
If you're on a PC, there's "KillWhite" plugin:

Also, SuperPNG for Mac and PC:

Note: Have not used any of the above.

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Last edited by vid2k2 : 05 May 2013 at 09:55 PM.
Old 05 May 2013   #5
Thanks for the suggestions.

The Photoshop plugin alternative seems the quickest and best option for my problem but I'm kind of screw......

I'm in a Mac and Photoshop CS6 and I'm looking for compatible plugins that do this.
Kill white, peel off white, etc. Development of the plugins seems to end at CS5...

Maybe the quick and dirty trick will work....

Thanks, If you know of any other mac plugin that could work would be appreciated.

Fernando J. Velarde

Old 05 May 2013   #6
Load up the image, go to your channels palette, ctrl + click on any single channel (or copy paste it into a mask channel) to load it as a mask then create a layer mask with the result on a solid black colored layer.
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Old 05 May 2013   #7
all you need to do is go to the channel palette and press the "Load Channel as Selection" button then press Delete
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Old 05 May 2013   #8
Actually you can do that in one stroke if you create a macro for that in PS
Old 05 May 2013   #9
In my experience, loading a selection through it's channel(s) isn't 100% accurate at all.
The image gets eaten away around the edge (very visible when it fades out like a shadow).
Or am I missing something?

Old 05 May 2013   #10
Thanks James and Per- Anders.

My workflow was more or less what you suggested but like [UP] Comments it's not 100% accurate but I can tweak it a little with the defringe option and some manual love.

I thought I could set it up from Cinema differently but I guess I can't escape the Photoshop work...

Those plugins that people suggested look great but I guess they are not updated for me.
Hopefully someday they will work in CS6. I fire up Cinema once a year for this kind of work so I thought I was missing something. I have to relearn the shadowcatcher thing everytime... ja


Fernando J. Velarde

Old 05 May 2013   #11
Using one of the RGB channels from the AO pass as a mask for a black solid color should give you 100% accurate results.
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Old 05 May 2013   #12
I might be missing something here... but can you just multiply the layer over the top of the image and background..

Old 05 May 2013   #13
I dont think you can multiply it over a transparent picture, since it contains no color information there.

Maybe I am missing something after long work hours but isn't it also possible to use the inverted AO-Pass as an alpha on the AO-Pass?
Old 05 May 2013   #14
Originally Posted by sszyszka: Using one of the RGB channels from the AO pass as a mask for a black solid color should give you 100% accurate results.

Maybe I'm not following you… But it doesn't work for me when trying the following:

See files attached, one is the original AO pass from Cinema,
the other is the image masked out by using the selection from the RED channel
(to show the difference better I added a white layer underneath so the transparency isn't visible).

I agree when you render an image from Cinema including an alpha mask you can grab the selection from the (hidden) alpha channel and mask things out perfectly.

But it won't work with an AO pass, I'm guessing it's because you'd need the combined selection of all three channels (they add up).

Attached Images
File Type: png ORIGINAL AO PASS.png (32.5 KB, 9 views)
File Type: png MASK FROM RED CHANNEL.png (18.1 KB, 9 views)
Old 05 May 2013   #15
I figured something out which gives a better result, but still not 100% accurate.

Same idea as before, but this time I hit select all then 'intersect from selection' (on mac > command/option/shift so you see the little 'x' symbol besides your cursor) all RGB channels, Red/Blue/Green PLUS the combined RGB channel also, then invert selection and create mask.

Result attached.

Attached Images
File Type: png ORIGINAL AO PASS.png (32.5 KB, 6 views)
File Type: png MASK FROM ALL CHANNELS.png (24.3 KB, 8 views)
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