Simon Ubsdell
6
COW Coins
Forum Replies Created
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[Robin S. Kurz] “That is what is called a “Difference Matte”, yes. The sloppiest form of matting by far, unless you’re using a) uncompressed footage and b) the camera is most definitely locked 100%. In which case you simply place one clip on top of the other with the top one set to the “Difference” blend mode. That will (or should, given a and b are met) a black and white matte which you in turn can use as a matte for either one after the fact.”
While this is correct, it is only part of the story.
The Difference Blend Mode will create the basis of a matte but it will be full colour and not the grayscale image that is needed for a matte. It will look like this:
The extra steps needed are as follows.
Make a group containing your two plates, in which you have applied a Difference Blend Mode to the top layer.
Clone this group and hide the original group. Call your new group Difference Matte. Duplicate the clone two times (don’t clone it!).
Add a Channel Mixer filter to each clone. Set the switch at the bottom of Monochrome. Set the top layer’s Channel Mixer filter to Red-Red 1.0 and everything else to zero (apart from the Alpha-Alpha value which needs to be left at 1.0). Set the next layer’s Channel Mixer filter to Red-Green 1.0. Set the bottom layer’s Channel Mixer filter to Red-Blue 1.0.
Finally set the Blend mode for the top two layers to Add, leaving the bottom layer set to Normal.
The result is your Difference Matte.
You now simply need to create a new group containing the source image that you to isolate and any background you want to use. Add an Image Mask to your foreground layer and add the Difference Matte (group) to the image well, making sure to set the Source Channel to Luminance.
The raw Difference Matte will almost certainly be inadequate without some extra work so you will need to add a Levels filter to the Image Mask to punch up the whites (White In) and/or crush down the blacks (Black In).
Here’s the Raw Matte and then the Raw Matte with a Levels filter applied to make it solid:
Robin is quite right in saying that a Difference Key is a very rough and ready effect and should be avoided wherever possible but sometimes it’s the only way of isolating a foreground object (other than roto) so it’s a technique well worth knowing.
Simon Ubsdell
tokyo-uk.com -
I’ve just done a test project of this kind for an arm-mounted HUD and I think I did everything wrong – luckily it was only a test!
You definitely want something very specific for the hands to point at – rather than just waving them around in a general direction and hoping for the best. Otherwise you have to design your interface around what the hands have done, which is really not ideal!
Your idea of using glass is a good one – and marking up the glass with the areas where you want “controls” for the hand to interact with would be the way to go. Having the hand stay on the right plane is less of a challenge than having it point to where the design elements are going to be. You’ll have to roto out whatever you mark on the glass so best keep it discreet.
Simon Ubsdell
tokyo-uk.com -
I hope that helped. Just to clarify what’s happening with the Overlay Blend Mode in this scenario.
Overlay uses a combination of the Screen on the lighter pixels, and Multiply on the darker pixels and applies each mode at half-strength, the result being that 50% gray values will be transparent.
The Motion reflection however disregards the Blend Mode of the layer and will still be visible – note that it has its own Blend Mode option.
Simon Ubsdell
tokyo-uk.com -
Faking turbulence is a lot harder in Motion than in Ae but I’ve had some good results using the Vortex behavior, as in this tutorial:
I’ve also experimented with adding a Randomize behavior to the Emitter position in instances like this – so the particles get sprayed around in a more organic way.
I’ve also tried adding Randomize to the XYZ parameters of the the Wind behavior.
In each of these cases it’s a good idea to experiment with having the behavior only kick on for specific parts of the animation rather than applying even throughout – it’s the kick factor which will give the particles the look of having been hit by an atmospheric event.
Simon Ubsdell
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The trick there is to set the Blend Mode to Overlay and the Color of the floor to mid grey – which is not, as you might have thought 0.5/0.5/0.5 but rather 0.54/0.54/0.54.
https://tokyo-uk.com/Motion/ReflectionOnly.002.zip
That works – obviously you need to make sure that your Gradient BG layer is not casting reflections.
Overlay with grey is a very useful trick to know about for this kind of thing.
Hope that helps.
Simon Ubsdell
tokyo-uk.com -
Just make your floor black.
If you need to kill the alpha channel of the floor (so that the reflection sits on a different background), set its Blending to Preserve Opacity.
Here’s that in action:
https://tokyo-uk.com/Motion/ReflectionOnly.zip
Simon Ubsdell
tokyo-uk.com -
Here’s a test project that shows you how to do the bounce technique using Oscillate behavior (set to half range) for the bounce and a Ramp behavior for the Amplitude (to slow it down):
Hope that helps. Let me know if that’s not what you meant.
Simon Ubsdell
tokyo-uk.com -
Great, thanks for the explanation. Makes perfect sense.
Great job – and I really loved the music video as well. Outstanding stuff!!!!
Simon Ubsdell
tokyo-uk.com -
[Bill Davis] “I will put it out there, however, that it seems that in this corner of the internet, X has to be “as good” as AVID or PREMIER on “their” terms. Yet nobody ever demands AVID or PREMIER have to be “as good” as X on X’s terms.”
I will perhaps surprise you, Bill, by agreeing with everything you’ve said there. Almost.
The only thing that I wish could happen is that we could simply dispense with the whole “better/as good as” rigmarole and simply celebrate the different ways in which different applications deliver interesting and worthwhile solutions.
I guess that would mean closing down this forum, so maybe that’s not such a good idea.
By the way, I really don’t hold a candle for Media Composer despite having somehow been cornered into defending it – frankly I think it should be a lot better than it is and I think that the folks at AVID still don’t get it. On the other hand, they certainly do by and large deliver the product that their customers want, which in its own way has to be a good thing. If no software vendor delivered what customers thought they wanted but only what they thought they needed, I’m not sure the world would necessarily be a better place.
I would just like to say that if you’re looking for exciting innovation, the guys at Adobe are positively scorching up the ground in the pace of development of Premiere and that too is something that needs celebrating from time to time.
Let’s all try and understand what’s great about FCP X (and there’s plenty to like, I’ll be the first to admit), but let’s try not to do it in the context of trashing the competition. At least that’s what I’ll continue to try to do, but I should probably absent myself from this forum for a while, I feel.
Apologies all round if I have offended.
Simon Ubsdell
tokyo-uk.com -
OK. I have misunderstood everything you have been saying.
I apologise unreservedly and sincerely.
Simon Ubsdell
tokyo-uk.com
