Pro colorist explains rolloff

I have a confession to make I was walking around for years as a working colorist Without Really exactly understanding what people meant when they used the term roll-off I'd kind of picked things up from Context and had a general understanding that it's a thing that happens in Shadows and highlights and sometimes it's a thing that we like and sometimes it's a thing that we don't like and when the conversation would come up I would just kind of like nod my head and hope no one asked me any direct questions and maybe I'm on my own but I have a hunch that a lot of us are in that category of not exactly understanding what roll-off is that's what I want to remedy today I want to come to a simple and concise definition of what Roloff is and why it matters to us as colorists so we're not going to be doing much Hands-On grading today we're really just going to be focusing on using DaVinci Resolve as a kind of visual aid for getting a clearer understanding of what roll-off is and the role that it plays in color grading before we dive into resolve if you haven't had a chance to subscribe to this channel yet May make sure you do make sure you turn on your notifications I do two new videos a week here talking about every aspect of the craft of color grading and we do a live q a call grade school every Friday morning where we talk about the subjects that we've been exploring in the rest of the week so lots of great stuff stuff you don't want to miss if you are interested in color grading or the color page inside of DaVinci Resolve all right let's dive into resolve and talk about roll off so I'm going to pull up my Scopes here so that I can visualize what we're looking at right now which happens to be a chart that I am producing from my exposure chart dctl this is a free download that you can grab from the link that I'm going to leave in the description for today's video and you can see that right now effectively what I'm doing is rendering a very simple sort of virtual scene if you like and in my virtual scene I have 13 distinct patches of gray that I am separating out in units of one stop and so in effect I have a scene with a dynamic range of 13 stops I've got middle gray in the middle six stops below six stops above but I've already got a problem don't I my problem is that if I want you to believe me that I'm producing 13 stops of dynamic range you're just going to have to take my word for it aren't you because we can't see any difference between these upper patches they are identical in value well why is that happening what's going on the problem that's coming about is a very common problem when we were talking about color grading and image mastering in general we have a dynamic range of a scene or of a source or of a camera and then we have the dynamic range of our display and the two don't agree our display has less dynamic range than our source and that's why in this case I have a point where my nice gentle slowly climbing curve here in my waveform just crashes right through the ceiling and I've got a flat white line right and we can see that represented here visually by these patches of gray that I really can't discern any difference between at all right this is where roll off comes in because our challenge is that we want to preserve this relationship in the middle down here in the middle of our tone scale this is where things like skin and human subjects and really the important things that we've intentionally exposed in our frame that's where those things are going to live and we generally want to leave those things at the level they are at and we want to preserve the relationship between these patches in this area because this is the body the meat the center of the image right so if we want to get these values pulled back in we're going to need to do something other than just grabbing like for example our gain wheel and pulling it in because you can see all right I pulled the gain wheel in and at least I can prove to you that I'm not a liar at least I'm proving to you that there actually are distinct patches of gray up in this register but look at what that's cost me look at how far I've had to move every single one of these patches in order to get the very brightest patches to reproduce on the screen that's a pretty gnarly compromise and one that we we don't want to have to make this is where roll off comes in what Roloff says is that at a certain point in the tone scale we are going to slowly start to reduce the distance between these patches so that we are reducing contrast in that area but we are maintaining contrast or the relationship between tones in the middle of our tone curve okay here's what that looks like in resolve I've used a color space transform to do some luminance mapping now check out what happens when I turn this on all of a sudden I can perceive the individual stops that were obscure to me just a minute ago here visually and you can see in the curve that my waveform is drawing for us that I have rolled off those highlights this shape that you see right here is where that term comes from this is what roll-off really means is we are taking the relationship between these patches and we are closing the Gap you can even see look the relationship is getting smaller and smaller and smaller and smaller so we are losing contrast in the upper register of our tone scale but we are gaining the ability to discern distinct patches distinct tonalities and that loss of contrast is only coming up in this region and our mid scale or our mid-tone contrast down here is remaining almost completely untouched as you can see that's roll-off that is the fundamental definition of roll-off is it is a way of taking large dynamic range and compressing it into a smaller dynamic range in such a way that we can see the details that we want to see from the original image but without completely darkening or flattening out the entire image okay that's the fundamental definition of roll off and really what we've just done here is one of two forms of roll-off that I want to talk about today it's a technical form of roll-off this roll-off has some parameters to it and maybe there's some taste or some judgment calls involved but it's really just a technical form of the use of the term or the use of the tool I should say because all I'm trying to do is fit the camera or the source into what the display can do right it's really not creative in nature but roll off can actually come in another form roll off can come in a creative form so we can say that hey in addition to the technical the technical tone mapping necessary to fit my scenes dynamic range into my displays dynamic range I actually want to introduce some additional roll-off let's take a look at how that would work I'm going to turn my Clips on here for a second and go to a fresh clip and if we look at this image right now we can observe that I'm already mapping it I'm using the same luminance mapping scheme that I was using just a moment ago on our chart and you can see that in turning this luminance mapping on I'm doing a much better job of holding on to these crazy highlights out this door than by having no tone mapping at all so I'm doing exactly what we were doing in the prior shot this is just technical roll off now what if in addition to this I want to shape the contrast in the highlights even further there's lots of different ways we can do this but one great example of how this might work would be to use my Kodak 2383 Lut I'm going to leave the link for this Lut in the notes for today's video as well this is a free download you can grab it's a great look to work underneath especially if you are working color managed like I encouraged doing here on the channel so this is my 2383 Lut and this is going to indeed introduce a form of creative or preferential roll-off and if we want to get a better sense for how that works let's turn off our output transform for a moment turn this Lut off and I'm going to turn our handy dandy chart back on for a moment just so that we can see a grayscale ramp for a second and we can now look at the way that this Lut affects this ramp you can see that my highlights are being rolled off you can even see up here visually I'm flattening things out I'm flattening out the contrast or the distance between these patches in the upper section of the tone scale and if I go back to my image here with everything flipped back on you can see that even though I'm increasing the overall kind of brightness in that area as my mid scale contrast is increasing I'm getting what I would call a flatter or a matter reproduction of my highlights it doesn't have as much ping to it it's more of a creamy highlight especially if I were to go in and adjust my exposure using offset for this image and start to bring that in a little bit like so you can see that that highlight is really flatter in nature than it was a moment ago so that's really the other form of roll-off that I wanted to emphasize is that in addition to being imparted on a technical basis which is often necessary for fitting dynamic range of scene into dynamic range of display we can also have creative roll-off that we introduce using something like a Lut or we could even do this by hand if we wanted to I could go to my custom curves pin some kind of control point and say hey below this don't move my contrast but above this I want to roll things off like so I'm just going to add another control point to keep everything below here nice and pinned let's try something like this you can see I'm getting that sort of familiar rolled off shape and I'm going quite far with it at the moment but this would be a more extreme example of preferential roll-off maybe I want that really creamy flat matte reproduction in my highlights and if I did this would be a great option I could also do the same thing down in the bottom end again I'm going to go kind of extreme here but I'm going to pick up the very bottom and I'm going to add a control Point that's going to keep this mid segment of my curve at the original slope that it had before I started doing anything at all but down here in the bottom I'm flattening out my shadows and merging them closer together so this would be a very extreme but hopefully very clear example of preferential or creative roll-off that you can impart either using your tools right within resolve or by using something like my Kodak 2383 Lut so those are the two forms that roll off can come in and most importantly I hope we've got a better understanding of what exactly we mean when we say roll off and why it's important and why we really can't do without it when we are color grading there are just far too many instances where we want to flatten out contrast in the bottom or the top of our image either for technical or for Creative reasons but we want to maintain strong mid-scale contrast and just as a closing note I'll point out that maintaining that strong mid-scale contrast while flattening out or reducing contrast and preserving detail in the very bottom and top of the image that's one thing that film does really really well that's one of the main things that we respond to and want to get when we say we are going for a filmic look is that strong eye-catching mid-scale contrast paired with a retention of highlights and shadows as we approach the bottom or the top of our dynamic range of our display so I hope that arms you with some clearer Concepts some clear ideas of what roll-off is the different forms that it can come in and it helps you to be a little bit clearer on roll off and its application in your upcoming color grades if you enjoyed this video if you enjoy videos about color grading in general make sure you subscribe we've got lots of great content coming out here on the Channel all the time like I talked about and you want to make sure you don't miss it so turn on your subscribe turn in your notifications and I'll see you here on the channel very soon

Channel: Cullen Kelly

Views: 22,267

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Id: ezCRBUioz68

Length: 12min 1sec (721 seconds)

Published: Mon Apr 10 2023