Contrast and Pivot in 3 Levels of Difficulty | DaVinci Resolve

welcome my name is avery peck and today i'll be explaining the contrast and pivot controls in three levels of difficulty let's get started let me go ahead and pop out our waveform so we can see what's going on a little bit better so let's come down to these controls and if you don't see contrast and pivot make sure you're on the first page of this little toolbar down here no contrast is fairly straightforward if we bring this up we can add contrast to a shot and if we bring contrast down we can reduce our contrast until eventually everything meets and becomes a uniform gray now a quick trick is if you want to reset a control you can double click the name of it and that'll bring it back to its default value first off what does it mean to add contrast to an image well contrast is just the difference in luminance or brightness between colors so when we add contrast what we're really doing is we're making bright things brighter and dark things darker you can also see that on the waveform here if i reset this and i bring my contrast up you can see that highlights are being pushed up and shadows are pushed down this is why you'll often hear the phrase expanding your contrast which is just another way to say that you're adding contrast to a shot now if we go in the other direction and we reduce contrast you can see the opposite happens that bright values are lowered and dark values are lifted until eventually everything meets in the middle this is called flattening your contrast again just another way to say that you're reducing contrast in an image so now we need to figure out what the pivot control does so you may have noticed that when i take my contrast control up and down that everything moves around this invisible center line or this midpoint that midpoint is the pivot so when i'm adding contrast anything above the pivot gets pushed up and anything below the pivot gets pushed down and importantly no matter what i do on this control anything that's right at that pivot point stays the same in other words the pivot is how we decide where we want to add contrast so a low pivot is going to expand our contrast from a very low point in the shadows so as you can see only the darkest shadows are being pushed down and the rest of the image is being pushed up and conversely if we set our pivot really high now only the brightest highlights are being pushed up and everything else is being pushed down so we're basically expanding contrast uh in the highlights and of course we can set it somewhere in the middle now typically speaking you want to set your pivot so that the overall exposure of the shot and especially the exposure on your subject is the same as it was before and there's two ways to do this i think oftentimes you can best do it just by eye by introducing a little bit of contrast and then just kind of setting this pivot here and you can also hit control d or command d to toggle your node on and off so you can get a before and after and i think that's actually pretty close you can see that as i add contrast we do get a punchier image but the exposure on her face overall is about the same as it was before the second method is to actually use the scopes now there's a fairly close correlation between these numbers that you see on the side of the scope these 10-bit values and the decimal value in the pivot control now they're not exactly the same but they're pretty close so if the exposure on our face is say you know around 384 or so then we can set the pivot to 0.384 and that should be pretty close to correct and then from there you can maybe just do a few little tweaks to taste so to quickly recap the contrast control allows us to expand or flatten our contrast and the pivot control decides where we expand or flatten our contrast from so a low pivot will expand contrast in the shadows we can expand it in the mid-tones or in the highlights and as a general rule of thumb we want to set our pivot to the same exposure as our subject so that the exposure on our subject doesn't drift or change as we add or reduce contrast now let's kick things up a notch because in reality there's quite a bit more to contrast and pivot than meets the eye so for this next section take a look at these gray steps here on the side of the waveform and pay attention to what happens if i take contrast up you can see that as we would expect everything is expanded around that pivot point but our white and our black patches don't actually move they're not affected by our contrast adjustment and as things get closer to white and closer to black they become flattened and kind of compressed now if i take contrast down below one you can see that everything is flattened or compressed uniformly so our white and black patches are now affected and everything is flattened in a nice linear fashion so to see exactly what's going on i'm going to flip over to a grayscale ramp and this will let us see the exact contrast curves that are being created here on the waveform so let's bring our contrast up and you can see that we get this nice s-curve shape so an s-curve is kind of unique in that it expands contrast around the pivot okay around this mid-point but it gives us this nice roll-off in the highlights and shadows to prevent clipping which i like to call the shoulder and the toe although you'll often hear different terms used by different people now if we adjust our pivot you can see that the shape of this s-curve changes to expand contrast in different tonal regions so if i bring my pivot up high you can see that we have a very short shoulder very short roll off in the highlights and a very broad roll-off in the shadows and this will allow us to expand contrast in the highlights while still not worrying about clipping anything and of course if i bring my pivot low the opposite is true where we get a very short roll-off in the shadows but a very long gradual roll-off in the highlights now something interesting happens when i take contrast in the other direction so if i take it below one you can see that instead of an s-curve everything is perfectly linear now if we adjust our pivot you can see that kind of interestingly the pivot basically functions like an offset now pivot is still doing what you would expect so if i set my pivot low and play with my contrast here you can still see that you know everything is being expanded around this low point here now one more interesting thing is that we can actually change the behavior of our contrast control inside of our project settings so if i open up our project settings and head over to general options and scroll down a little bit there's a setting called use s-curve for contrast and it's going to be enabled by default if i disable this and click save you'll notice that the contrast control is actually linear in both directions instead of using an s curve above one now it's important to note too that this is a project wide setting it's a global setting so you can't adjust this on a per shot basis you basically set it for the entire project so at this point i'm sure you're asking why right why would i use an s-curve over a linear expansion or vice versa and what are some of the advantages and disadvantages of both so for s-curves the biggest advantage really is this roll-off that we get in the highlights and shadows this allows us to introduce contrast into a shot without worrying about clipping information and if we come back to our other shot here this is particularly useful for shots like this with bright highlights and dark shadows so turning our contrast up you can see that we get lots of contrast but nothing is going beyond our scopes here right nothing is actually being clipped now one of the major disadvantages of an s-curve comes from the fact that it's a non-uniform expansion basically meaning that it doesn't expand everything the same way across the full tonal range of the shot we expand contrast around our pivot but we're actually flattening and reducing contrast in the highlights and shadows this means practically speaking that it kind of messes with the tonality of the image in different ways particularly if we're adjusting our pivot or using different pivot points for different shots and we're going to explore that a lot more in the advanced section of the video in just a minute now linear contrast has its own unique set of pros and cons linear contrast is what we call a uniform expansion meaning that it expands contrast across the full tonal range of the shot in a completely consistent uniform fashion basically in other words the highlights mid-tones and shadows all receive the exact same amount of contrast now practically speaking this means a couple of things for starters linear contrast is extremely consistent and predictable it's also pivot agnostic meaning that if we change our pivot point the way in which contrast is being expanded doesn't actually change again with an s curve when we change our pivot it changes the fundamental shape of that curve but with linear contrast we don't have that problem so no matter what we set our pivot to we're actually expanding our contrast in exactly the same way now because of this consistency and uniformity there are many colorists that believe that linear contrast preserves the original image better so if i jump back to our original shot you can see that as i play with my contrast control that everything is as we would expect expanded and flattened in a linear fashion so all of the lighting ratios that the dp established on set are all essentially preserved right the relationship between the highlights mid-tones and shadows remains the same everything remains equidistant the main disadvantage of linear contrast though is that we no longer have a roll-off so it's very easy to clip values particularly with shots like this where we have bright highlights and dark shadows so bringing this around full circle the question is when do we reach for one over the other now as a very general rule i like to use linear contrast whenever possible and then if i still need to add contrast but things are close to clipping then i'll reach for an s curve and chances are you'll actually be using both inside of the same node tree so if i close this real quick a very common strategy is to create a single global s-curve for all of the shots in your project and then do your balancing and shot matching using linear contrast before that s-curve to kind of elaborate on what i mean let's say we have two nodes and in this first node this is where we'll do our balancing and then in the second node we'll have some kind of display transform so this is probably something to get us from a log space into say rec 709 now usually this transform will contain some kind of s-curve this could be an s-curve that you draw yourself this could be you know an s-curve that's embedded inside of a lut if you're using a lut to do this even if you're using a form of color management like color space transform or asus all of those will apply their own curve to the footage but the idea is exactly the same we have some sort of s-curve as part of our transform and this s-curve is used for every single shot in the project so every single shot has the exact same s-curve applied to it and then when we balance our shots we use linear contrast so you can either use contrast and pivot set to linear mode or you can even use other tools like gain and offset or even lift and gain which we'll explore a lot more in just a minute but the main advantage of this is you get the consistency and uniformity of using linear contrast but you also get the nice roll-off of an s-curve all right so we've made it to the advanced section and at this point i want to elaborate on some of the discoveries we've made so far and also talk about a few of the finer points of these controls so firstly continuing our discussion of workflow i mentioned that you can add linear contrast to an image using other controls and i want to demonstrate that real quick so if we come over to our grayscale ramp you'll remember that the contrast control in linear mode of course expands or flattens an image linearly and the pivot control functions the same as an offset now you may already know that the gain and offset wheels can perform the exact same functions so the gain wheel will expand or flatten an image linearly and the offset wheel will shift everything up and down the same as pivot so what this means is we can use our gain wheel as a contrast control and then we can use our offset wheel as a pivot or as i like to think of it as an exposure control to make sure that our exposure remains consistent as we add a reduced contrast now to quickly show you what this looks like if i take my gain up a little bit we're now adding contrast and then i can take my offset back down so that the exposure of her face remains consistent and if i a b this node you can see that we've now added a little bit of linear contrast to the image now alternatively we can also use gain and lift so gain will scale an image linearly from the white point and lift will scale it linearly from the black point and so we can actually get the exact same net result just using a slightly different approach although personally i find that gain and offset is the more intuitive approach now one of the advantages of working this way is that it allows us to keep our contrast control in s-curve mode which is probably the most convenient way to add an s-curve to an image i also find that the gain and offset wheels are better for balancing images quickly particularly if you're using a control panel the second big claim that i want to elaborate on is the idea that s curves can mess with the tonality of an image and i want to show you a few different examples the first and arguably simplest example is the idea that aggressive s-curves can cause highlights and shadows to sometimes look clipped so with s-curves there's a direct give-and-take relationship with contrast because as we expand contrast around our pivot we also have to flatten the extremes of the image more aggressively to prevent clipping now to show you what this looks like visually let's come back to our original shot here and i'm going to take my contrast up to something high like 1.5 or so now if i close this real quick and we kind of zoom into our image here and i toggle this node on and off you can see that in the highlights you know some of these fine details with her hair for example become harder to see to become kind of blown out and the same is true with the shadows right so you know little details here like in her hair are definitely crushed down and they become harder to see and the more contrast we add here so i'm using my control panel but if i push contrast even harder this effect becomes more pronounced right so now it's very hard to see any detail in these shadows and also in the highlights now this is one of those things that you might actually miss it if you're not paying attention because technically nothing here is clipped right everything is still within our display range nothing's going beyond the scopes the problem though is that there's a direct correlation between detail and contrast we need contrast in order to see detail so when we flatten contrast in these areas too aggressively it becomes harder and harder to see detail and eventually gets to a point where these areas look clipped even though technically they're not so for this reason i think it's important to always be aware of how aggressively you're pushing your s-curves and personally i like to use them as sparingly as possible to prevent this problem now there's a second example of where s-curves can mess with tonality and this one is more subtle it can kind of sneak up on you a little bit if you're not careful so if you recall from earlier when we're using s-curves and we change our pivot the shape of that s-curve fundamentally has to change in order to accommodate that new pivot point so what this basically means is the exact characteristics of our contrast expansion are constantly changing with pivot so coming back over to our shot here what i'm going to do is add a fixed amount of contrast so say 1.3 and what i'm going to do is only adjust the pivot point so for this i'll set the pivot point to say 0.3 and i'll grab a still of that and then i'll set my pivot to something higher like 0.6 okay so what i want to do here is i want to try and match these images as close as i can and show you the subtle differences in tonality so let me close my scopes real quick and let me just bring them up here so um there's a couple of ways that we can match these um because the black points and white points of the two images are fairly similar i think we need to just do some stuff in the midtones here so we could try to use like the gamma wheel if we wanted to and lift maybe but i think it might actually be easier to just use the uh the curves here so i'm going to take these mid-tones up a little bit until the exposure on her face is a close match and i think that's pretty close and then i also want to match these shadows here so bring my black point down a little bit and this seems like a pretty close match in terms of exposure so now if i toggle this still on and off it's subtle let me full screen this for you but you can see there are differences subtle differences in the tonality between both images so the black point is basically the same the white point is basically the same the exposure on her face is the same but the transitions between those areas are all a little bit different and this effect becomes more pronounced as you add more contrast now whether or not these small changes in tonality are an issue is really up to you i think the classic rule always applies which is that if a shot looks good then it is good right so if you're using different s-curves on different shots but things still look good and your client's still happy then at the end of the day that's all that really matters but i think regardless it's always good to be educated about these things so that if it does become a problem you know how to diagnose it and you know how to solve it i also want to take this opportunity to quickly show you that linear contrast does not have this issue so let me go ahead and reset my grade here and in my project settings i'm going to go ahead and switch my contrast control over to linear mode so if i do the same thing as before and i set my contrast to 1.3 and i'll set my pivot to 0.3 i'll go ahead and grab a still of that and then i'll set my pivot to 0.6 and i want to match these two images so i'll play that still and literally all i have to do is move my offset until the exposure on her face is a match and now we have basically an identical match right so i could even make another very very slight adjustment there and you can see if i play the still and i take it on and off that these two images are literally identical so this is one of the big advantages of using linear contrast and linear operations in general we preserve the qualities of the original photography a bit better and there isn't a risk of running into these little gotchas when it comes to things like tonality and then of course if this was a real workflow at the end of this you would probably have something to provide some kind of roll-off so that could be an s-curve or you could even just use like your soft clip tools here to provide a gentle roll-off in the highlights and shadows and as long as you keep everything linear before that then you basically get the best of both worlds right you get the consistency of linear contrast and using linear transforms but then you get the nice roll-off of an s-curve or in this case your soft clip and with that we have finally reached the end hopefully this video was informative for you and you learned some new stuff about the contrast and pivot controls if you'd like to stay up to date on new tutorials and personal projects you can follow me on instagram at avery peck official and in the meantime i want to say thanks for watching my name is avery peck and i'll see you in the next one [Music]

Channel: Avery Peck

Views: 54,005

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Id: VSlkFWtADx4

Length: 23min 15sec (1395 seconds)

Published: Thu Jan 28 2021