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Creating a drop shadow on a 'mode: multiply' (white background)

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Olly Lawer
Creating a drop shadow on a 'mode: multiply' (white background)
on Feb 20, 2012 at 9:17:27 pm

Hi,

I've imported some clips of some cogs - just brushing up on expressions. Pulled them from the internet just for the purpose of playing with 3 different size cogs and getting them to rotate in unison at varying sizes.

All good so far - works a treat. When I overlaid one cog on another, I got around the problem of the white background by changing the mode to multiply. However, now I have tried to add a drop shadow, I see by issue. It's trying to made the drop shadow around the whole shape (inc white background) and not the cog.

Auto Trace doesn't really help as it masks round the whole image (inc white) and even changing the settings only achieves a mask that is only just useable.

Is there a way around this problem? It doesn't really matter for this project, but it would be useful to know for future work.

Thanks

Olly Lawer


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Olly Lawer
Re: Creating a drop shadow on a 'mode: multiply' (white background)
on Feb 20, 2012 at 9:54:17 pm

Btw, managed to get auto trace to work in the end, but applying a drop shadow still didn't work. Thought this might be to do with render order, so precomposed applying drop shadow to precomp but same issue.

Olly Lawer


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Roland R. Kahlenberg
Re: Creating a drop shadow on a 'mode: multiply' (white background)
on Feb 21, 2012 at 10:56:24 am

The other options - off the top of my head:
1) Use Photoshop
2) In AE: apply Shift Channels and select an appropriate Channel to use for the Take Alpha From parameter. An appropriate Channel is defined as one that looks either most similar or dissimilar (use Invert immediately if this is the case) from what your Alpha Channel should look like.
Apply Levels and set its Channel to Alpha and tweak the Input Black or Input White to suit your needs. Use this layer as a Track Matte for the original layer.
3) Rotobrush

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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Jon Bagge
Re: Creating a drop shadow on a 'mode: multiply' (white background)
on Feb 21, 2012 at 3:59:29 pm

You can also try a simple Luma Keyer. Set it to key out brighter, and play with the settings. You may need a Matte Choker or something to soften the edge.

When you say drop shadow doesn't work, what do you mean?

Also are you using the drop shadow effect or the layer style?
For a rotating cog I'd recommend the layer style. The effect gets applied before the transform and the layer style after.

If you're rotating something (unless the rotation is in the footage itself) using the effect will make the drop shadow rotate as well. So it will point in different directions which isn't how it should work. Using a layer style will apply the drop shadow after the rotation has been done, and it will point in the same direction no matter how you rotate or move it.

--------------
http://www.jonbagge.net
Jon Bagge - Editor - London, UK
Avid - FCP - After Effects


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Olly Lawer
Re: Creating a drop shadow on a 'mode: multiply' (white background)
on Feb 24, 2012 at 4:11:22 pm

Sorry for the delay.

The shape layer is square - white with a cog in the middle. I used modes to get rid of the white (multiply) but when I add 'effect' drop shadow, it is still round the whole shape layer (square).

I did try layer drop shadow, but that had the same effect.

Even when I masked round the cog using autotrace and deleting the masks I didn't need (5 were generated), it was still around the shape layer and not the cog.

I even tried creating a precomp of the layer (both moving all attributes and leaving them in the comp), but that didn't work either.

Scratching head. Going to start from scratch and see if I can fugure it out. Brining it in from Photoshop would probably work best as AE won't know the original shape - the square and only the cog.

Olly Lawer


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