Before working with a complex tool like the Lumetri “effect”, it is wise to understand what the tools do … how they’re designed to work, what they’re designed to affect, and in what order to use them. Lumetri is designed to be used top-down. Basic tab first, Creative second, and on down. Within each tab, the controls are also processed top-down (with one … interesting … exception). For this post, I’ll stick to the tonal controls, and will not deal with HDR or Saturation.
This top-down approach does affect the way you use Lumetri: if you set a “lower” control, then go back and make a change “above” it, the lower control may now do something a bit different than it was … it’s that order-of-processing thing. And keep this in mind … the Basic tab is designed to give a quick way to neutralize the tonal values of a clip, to get a “clean” and natural look to the image, before using the other tabs to make the clip pretty.
Before we begin, here’s a primer in ‘colorist’ controls. A colorist … as opposed to say an editor, is a specialist in making video look … something. There are basic, standard controls for changing the look of video in software, and they are the underlying tools of the Lumetri panel, with (mostly) a user-interface imposed on top so you don’t actually see the typical colorist’s UI tools.
The most basic are Offset, Lift, Gamma, and Gain. And they work (mostly) in ways similar to a Curves control box.
Offset: an Offset control lifts or lowers all Luma (brightness) values of the image the same ‘amount’. (There’s no comparison to a Curves box for this one.)
LIft: a Lift control moves the black point up or down, and has a proportional affect up the entire value range to the White point (which it does not move, unlike an Offset). It’s like grabbing the black point on the far left of a Curves control … raise the Lift control, the “black” end of the line gets higher … but the whole line black-to-white stays straight.
Gamma: a Gamma control moves the middle, and the effect ‘falls off’ towards the top & bottom, though most of the image will be moved at least a little … just the middle will move most. Used to say lighten the mid-tones while leaving Black & White points unchanged. Like grabbing the middle of a Curves control and moving it up/down.
Gain: a Gain control sets the White point … and like a Lift control, affects the entire image proportionately, affecting the highlights the most, mids less, and darks very little … it’s like grabbing the right side of a standard curves box and moving it up or down.
Now … we’ll examine the Basic tab controls in this post.
Input LUT
Yea, pretty simple … this is designed to accept not only the included ones in the build, but most any LUT you can use of the various LUT formats. I created a LUT from a Lumetri HSL key that I use for a quick “neutralization” color correction … it’s my top option in the drop down box. That’s covered in my post on Neutralization with the Tangent Ripple.
White Balance
This is our odd child … it’s actually processed at the bottom of this tab, but placed in the UI here at the top. This control is essentially a three-way curves control, as when you adjust the two sliders of Temperature & Tint, what it’s doing under the hood is adjusting the White points of the three channels, R, G, and B as you would with a Curves control of separate controls for each of the three channels. When setting White Balance, it’s helpful to have the RGB Parade scope showing in the Lumetri Scopes panel on the top left of the UI. You can actually watch the individual channel tops change as you adjust White Balance. I also always have the Vectorscope YUV “up” for color correction work.
Temperature: any change to this control changes the balance between the white-points of the Red and Blue channels … as one goes up, the other goes down. Lower the setting towards “blue”, and the Blue channel white-point goes up, the Red channel white-point goes down. Adjust Temperature towards “amber” and the Red channel white-point goes up, the Blue channel white-point goes down. This isn’t blue versus “amber” as the control looks like it is! It’s purely Red versus Blue.
Tint: any change to this control changes the balance between the white points of the Green channel and the white points of both the Red & Blue channels. Lower Tint towards green, the Green channel white point goes up, and both Red and Blue channel white points go down. Raise the Tint control values, and the Green channel white point goes down and both the Red and Blue channel white points go up. This isn’t Green versus Magenta, but Green versus Red and Blue.
White Balance has very little effect in the shadows, some in the mids, and most in the upper-mids and highlights.
Tone Controls
To show what these controls do I created a clip that is one half a group of tone-specific boxes and one half a gradient ramp of around 40 segments black to white in many small steps. After loading the clip, I opened the Lumetri scopes on the left side, but for this purpose with only the Waveform in Luma mode, 8-bit and Clamped signal. It’s the Luma scope that will show us exactly what’s happening when moving any tonal control.
Across the image, you see the Waveform (Luma) scope, the image in the Program monitor, and the Lumetri controls.
The left half of the scope (the boxes) is very useful to see where things are compressed and where they are stretched. The lines between boxes are all very evenly placed … until you make a change in the tonal values. The right half (the gradient ramp) shows any curve type change to the tonal values very clearly.
For this 8-bit image, 0 is black, and 255 is pure white. But for easier understanding, within this post I’ll refer to the value scale on the left edge of the scope … 0 is Black, and 100 is White.
Exposure: I raised the setting of this to 1.0, and this image shows the change that happened. This is a very … unusual … control. It’s not a “brightness” or Gamma control as most think it is, and it works very differently depending on whether you are raising or lowering the setting.
This is sort of like raising a Gamma control, but grabbing the “Curves” line at about the 75 mark on the 0-100 scale. Note that neither the White nor Black points change, and the effect is more prominent in the upper-mids/highlights, but it does stretch the Shadow values up a bit.
Now, I’ll lower the exposure to the -1.0 setting.
Ahh … very different! When lowering Exposure, it works totally as a Gain control, dropping the White point and everything else on the line towards black proportionately. Any movement of Exposure down is a straight-line Gamma-style adjustment.
Contrast: After re-setting the Exposure control, I set the Contrast to 100. This control works in the standard Adobe fashion, adding an “S” shape to the gradient line from Black to White, similar to the way film used to show on Densitometers … and yes, I spent years tracking film density on those!
Raising Contrast lifts the values above 50, and lowers the values below 50, but never moves the exact mid-tones nor the ends, the Black & White points. This creates a subtle “S” shape to the gradient, a slight curve to the tonal placement. Highlights are brighter and more compressed, while Shadows are darker and also more compressed. This sort of movement will slightly stretch the mid-tone values out.
For the next test, I set the Contrast control to -100. Look at the lines for the boxes on the left half of the scopes, comparing the image above and below. Note that in the above one for raising contrast, the lines at the far ends of the scale are closer together, and the lines in the middle of the scale are farther apart. For the image below with lowered contrast, the opposite happens: the space between the lines stretches at the ends and compresses in the middle.
Lowering contrast lowers the Highlights and raises the Shadows … stretching Highlight & Shadow values, compressing Midtone values, and creates a slight “reverse” S curve to the gradient line. Like before, it doesn’t change the total dynamic or contrast range of the image. The Black & White points stay the same.
Raising Contrast pushes data from the middle third towards the edges. Lowering contrast pushes data from the edges towards the middle third.
Highlights: After re-setting, I set the Highlights control to 100. As expected, raising the Highlights control does raise the highlights area but … note the little “scoop” near the top of the gradient ramp, and the way the space is still “neutral” for the top box of the left side, but very compressed for the next three. It’s not a smooth curve to the White point.
And look back to the “Neutral” image at the top of this post. Comparing the Shadow group of lines on the left side, it’s clear lifting the Highlights control lifts values clear down to 8 or below … a rather wider ‘range’ of values are changed than one might think.
I then set Highlights to -100. As shown below, lowering Highlights also affects nearly the entire scale though not quite as far down as raising highlights, and again, has a little curly figure at the top of the scale.
Much of the time, we wish to move only the Highlights a subtle amount up or down but not move the Shadows. In that case, if we move the Highlights, we may need to compensate by moving the Shadows control in the opposite direction. As raising Highlights also raises the Shadows some, we could slightly lower the Shadows setting to maintain the same look in the Shadows. And vice-versa of course.
Shadows: After re-setting the Highlights, I set the Shadows to 100. Raising this control is similar to the Highlights, in that it affects a wide range of data. But it doesn’t go quite as far into the highlights range as the highlights control goes down into shadows. From looking at the spacing between the lines of the boxes and the curve of the gradient ramp, raising Shadows stays closer to a “neutral” gradient in the upper midtones.
Now I’ve set the Shadows to -100. Lowering Shadows affects from the bottom to near the 90 level, way into the Highlights. Note that the bottom of the highlights box group, which is at about 74 in the “Neutral” image, is dropped to about 66 here.
In practice, a subtle raising of Shadows will not normally need an off-setting and opposite adjustment to the Highlights, but lowering Shadows will normally need an offsetting small lifting of the Highlights.
Whites: I reset Shadows and set the Whites control to 100. From looking at the scope, this is a Gain control, pure and simple. Perhaps the most straight-forward of the Basic tab controls, this is simply taking the white point on a Curves box, and moving it up or down with the proportionate changes to every other value on the scale. The line of the gradient ramp stays straight.
Notice, however, that it doesn’t lift any value above 100. That is clearly the top of the “scale” that Lumetri is allowed to control in a standard dynamic range setting. In HDR mode of course it can go higher.
After I set Whites to -100, it’s clear that lowering Whites is exactly the same in action … a pure Gain movement that drops the White point.
The Whites control is a very simple, obvious, and direct control. (I like obvious, direct controls!)
Blacks: I reset the Whites to 0 and adjusted Blacks to 100. Looking at the scope, this … is a very interesting control. Take a close look at the following image, as this is very different than the effect of the Whites control:
Raising the Blacks control can lift the black point clear to 20, but has very little affect above that. It does lift the “50” value bar to about 55, but does very little above there. And that’s not enough to be able to see easily with most media. Essentially, we’re lifting the “floor” and that’s it. But the bottom tones are such compressed data, that there is little detail or discernible difference between values in the “deep” shadows now. They are simply dark-ish grays of similar or at times now exactly the same value.
I then set Blacks to -100. And … again … a very different action from the controls. This is like doing a very specific Curves-tool use. Look at the box spacing for lowering Blacks (and the corresponding boxes in the Program Monitor): it can flat-line values, but look at how it’s pulled the data down. The first three boxes have been “flat-lined”, and the fourth pulled down to 8, the same level as the darkest shadow box in the original “neutral” image. The top box of the shadow section, which started about value 38, is down to 20, and the 50 marker-box is only down to 48, showing that this control has very little effect outside the shadows. We have “crushed” the darker values to simple black, but not done anything to the midtones.
Learning exactly what the Tonal controls of the Basic tab do individually and combined is the key to using this set of controls as designed: a quick way to neutralize the tonal values of a clip prior to making your clip look pretty using the Creative, Curves, Color Wheels, and HSL tabs.
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