Demystifying mattes, masks & alpha channels!

hello and welcome to video revealed I'm Colin Smith this is essential for anyone today in working with media and graphics motion graphics video editing this is demystifying mattes masks and alpha channels this one is based on all the questions I get about how to remove the background how do I get rid of this how do i isolate this first of all if you don't have green screen and you need to rotoscope that means drawing a mask around every single frame if you've never done that before get ready for a nightmare what looks incredibly simple in a visual effects real or on television of behind the scenes is brutally difficult but what I wanted to do is I wanted to clarify all the different terms for isolating a part of an image and that's all of these text note techniques are the exact same thing they're isolating isolate the background isolate the shirt isolate the skin isolate that remove that remove that all of that stuff use different techniques I'm going to show you in Photoshop and in Premiere Pro and After Effects I want to start by defining the term matte and that means to matte something out or to block something up here's a perfect example this guy is in this scene in Paris but actually that's what was shot and the rest was blacked out so that when they put the matte painting in he's going to fit right inside of there that's with glass and matte paintings that goes way back but that's how things used to be that's how you used to be able to remove that you had to do it in camera you would rewind the camera and then expose that again we don't have to do that but the same idea applies so here I have a car that was obviously not shot on a white background it was cut out of the background and has a mask so in Photoshop if you look on the right hand side you'll see a mask and what's important is if we zoom into these areas you'll notice that the very fine edge of something smooth like the edge of the car is not a hard edge although when we zoom out it looks like a hard edge it is not if it's a hard edge it looks fake and the difference here is between how many bits of information and if you've heard of the term an 8 bit image if you have an 8 bit mask or an 8 bit of alpha that means you have 256 levels of colour of black and white between white and black so it's not a hard edge a gif and yes I call it a gif or Jif that transparency is one bit and it looks like crap and it's a hard edge it's basically you're the technology says a pixel is turned on or and turned off and you pick one colour and that's the transparency but in Photoshop files and TIFF files and alpha channels in video in general you've got 8-bit transparency so you have a nice smooth transition between it looks more natural but in a hard edge like a car it still has a tiny bit of gray in the edge to smooth it on I'm going to show you an example of one bit alpha in a second now how would someone normally draw a this transparency they would do it with a pass so I'm going to turn everything off here and just show you the path so here is a vector path that was drawn as a mask a path by default is just that it is a path it can have a level of anti-aliasing on the edge and the anti-aliasing is what we're used to we don't see things that aren't anti aliased anymore in the computer but you they just look much better so with this as a pass you can't see the transparency but you turn it into a selection in Photoshop and then that selection turns into a mask but the path is a good way to draw that out so if you needed to save an alpha then here's where the alpha would be and if you need to save that in a format so in the file menu if I choose save as and we choose something like TIFF you'll notice one of the choices is to keep the Alpha channel if you don't have an alpha channel in your Photoshop files that option won't become available just so you know when you see that alpha Channel things show up it's like oh yeah I happen to have an alpha Channel not every format supports alpha channels JPEGs don't sometimes they will be stripped out Photoshop will remove things or it will give you an error that you have an extra channel that's in there so that is the Alpha Channel okay so if we look at this that's a mask the Alpha channel is a channel that's sitting there the mask is applying itself to this layer see how that works other programs that use that would use the Alpha channel need to turn that on so they would say yes use the Alpha Channel now let's look at one bit transparency let's go look at the difference between 8 bit and one bit transparency so we'll see the edges of her hair very soft and if we look at the mask you can see the mask is organic and beautiful and wonderful okay so let's turn that off and turn her on with one bit transparency look at the edges they look like garbage let's look at the mask that is a one bit mask you can see either the pixels are on or the pixels are off all right so that's alpha channels and that's mask now let's talk about mats alpha mat and luma mattes in Premiere Pro alright the first thing I want to show you is black and white this is something that looks exactly like a mask in Photoshop what we're looking at is a green-screen so if I turn on ultra key we've got a green-screen when I remove that green-screen then I can remove the background if I want I can turn on the transparency grid so we can see that level of transparency so this is a video that I'm removing the background but if I export this out that background will be solid black it won't have a checkerboard and won't have transparency unless I save it with an alpha Channel and that is not always an option you have to find a format that supports it one of my favorite formats in the new versions of Creative Cloud is the Cinna form GoPro Cinna form format one of the the options is to have 10 bit 12 bit with alpha so just to show you what this looks like in the ultra key effect you can look at the Alpha channel so that is exactly what it has alright so let's look at math you might recognize this from my other tutorial on using track mats and if we turn the track mat off then what you're looking at is an object coming up from the bottom and when I turn the track mat on that track mat effect simply tells the video to add itself to the track mat what's important here is that there are two choices mat alpha mat luma the mat alpha is the transparency so that black rectangle has a fixed size and after the size the Alpha is not there so it's based on the Alpha of that shape if this was a blurred rectangle then you would get a soft edge instead of a hard edge between that the color of this does not matter so this is a black rectangle let's go over here and look at this sequence that I have bunch of these in here if I open this up I purposely colored them red because it doesn't matter the color it matters what matters is the Alpha the transparency that's around the outside edge is what's hiding this and again if I turn the transparency grid off its over black okay so that is the Alpha Matt let's go and look at a luma matte so here I've got a video and on top of that I've got a black and white video it doesn't have to be black and white but I've got a black and white video and if I turn on the track mat for that you'll see the track mat simply says the video is inside the track mat and you can see it were not on alpha run luma if I invert that then the opposite takes place and if I turn on the transparency grid I've got a hole in my video if I place another video but beneath that then now it shows through in that hole you follow me so far that's a luma matte what is a luma matte based on the luminosity of whatever that is I'm using a black and white image well it's actually grayscale because there is a little bit of gray in those edges but I could throw in any image on top of this or any video or anything and that could be the luma matte as long as there's enough contrast there isn't enough contrast you could run an effect on the the image you're using as a luma matte and maybe convert it to black and white increase the contrast push the shadows down invert this is an enormous amount of control in track mats so that's good now let me have one last look inside Premiere Pro on a mask because we also have you haven't seen this tutorial that I added where I'm taking away the front of that car so I'm going to zoom in a little bit so you can see that and what we're looking at is a mask and the mask hides that if we turn the bottom off you can see we get transparency based on the mask okay one last thing to tell you about this mask it's not feathered but it's anti-alias you won't see one bit Alf remember that crappy looking Photoshop just by the very nature this mask and the masks that you would have in After Effects you if you have zero feathering you still have anti-aliasing you can't there's no reason to make these one bit they're just 8-bit by nature and they look good okay Wow so we're look we looked at masks alpha channels luma mattes alpha mattes and masking tools in Premiere Pro what is the holy grail of all of this rotoscoping oh let's go have a look at that in After Effects here I've got a video of a surfer and you see all of those little colored dots those are paths somebody did that by hand somebody manually moved and key Frank you want to see the key friends in this what it is look at this look at that look at all these freakin key frames in here okay so when someone asks me hey how do you remove the background when there was no green screen that's how you do it this could have taken hours days weeks or months of work I'm going to turn this to alpha so that we're looking at the Alpha look what's happening in this one we get the mask that was drawn around the surfer plus we get this soft edge around the actual spray how was that done well that was done let's go back to RGB this is using an extract effect see that so they use the actual splashing of the water and extracted a an alpha channel out of that because the water is kind of sort of almost black and white it's the spray and then a different color background so when you run that on that you can remove some of this this doesn't always work but in this example here how you going to draw a rotoscope around the spray you won't but after-effects is really the king of all when it comes to this level of masking transparency and rotoscoping it can do all of it it can do tracking matting luma alpha and use Photoshop files and stuff from from Premiere Pro that is the highest level and easily the most complex it's where you get the absolute best results for working with visual effects and removing alright but it's also the one that will just it's really hard stuff so please if you ask me how do you remove the background remember the surfer guy and all those millions of points in there and what it takes to do that so now hopefully you in your bag of tricks if somebody asks you for a luma matte alpha Channel a rotor scope or mask or mat you have a better understanding of how to deliver those two alright hopefully you found this informative if you're new to video reveal take a moment subscribe you want to support us a little more join us over on patreon for as little as one dollar a month till next time I'm Colin Smith and it's my job to get you [Music]

Channel: VideoRevealed

Views: 52,457

Keywords: Adobe Premiere Pro, Adobe Creative Cloud, Colin Smith, AdobeColin, video editing, VideoRevealed, video editor, edit video, alpha channels, mattes, masks, paths, luma mattes, alpha mattes

Id: rPk8k8LaXFI

Length: 15min 9sec (909 seconds)

Published: Sun Mar 05 2017