Thursday, December 31, 2015

Crushing Blacks Precisely - LOG and Curves in Resolve



The Zone System is a method of precisely identifying levels on the value scale from 0 (pure black) to 10 (pure white). It was created by two photographers, Ansel Adams and Fred Archer, around 1939 or 1940 as a tool that would allow them to ‘previsualize’ a final printed image before even exposing film.  


As a photography student many years ago learning to work with B/W film, it was the single most important tool I had in my conceptual arsenal. With that, I could make monochrome do anything. Without it, it was hit or miss. Mostly miss.

We’re going to use the Zone System, Curves and the LOG Menu to look at ‘crushing blacks’, a common term in film referring to depth of detail in shadow and the exact point at which detail falls off into an inky, detail-less void.


inside-llewyn-davis-movie-still-11.jpg


Often, blacks are ‘crushed’ with what seems to be a large, blunt instrument. It doesn’t have to be that way. Resolve gives a colorist a great deal of control over lower values. For example, looking at the chart at the beginning of this post, where - exactly - do we want to lose detail? Should we crush Zone 1 into Zone 0? Or should we go farther and crush Zone 2 down to Zone 0? Should we maintain an appreciable difference between Zone 2 and Zone 3? Or do we crush Zone 3 into Zone 2 and everything below that down to 0? 

Any of those decisions will have an impact on your film, how it feels, how it affects the sense of light. In the still above from Inside Llewen Davis, everything below Zone 3 is crushed into Zone 0, while still maintaining separation through the middle zones and a very high key outside the window. It’s an achievement.





How is this done?


As an example, I’m going to use this frame from a friends’ short film. It’s a similar scene to the Llewen Davis shot.


As we can see in the waveform, most of the data in the image is in the undifferentiated lower values. Our first - and most important task is to spread those values out so that we have something to work with.





The first thing I’m going to do is bring the saturation down to 0, so we are only looking at the tonal values.








In the Primary Wheels menu I’ll use the Gamma Wheel to push the values as far towards the middle of my waveform as I can without losing detail.







__________________________

Stretching out the middle tones


My next step is to use the Lift Wheel to drop the shadows. You’ll see immediately that the main effect of these manipulations is to stretch out the midtones in the image, like rolling out a pie crust.






Now we're beginning to see some differentiation in the the very lowest values - Zones 0 - 3.




Here’s how it looks with saturation back up to normal, just for reference.





__________________________


Primary Wheels


A brief tangent is required at this point. Until now, we have been working in the Primary Wheels menu - the 'default' color manipulation menu in Resolve. The Primary Wheels controls have an important characteristic which make them ideal for global manipulations - their 'jurisdictions' overlap each other to a very large degree. Because a change to the 'Lift' (lower values) overlaps the 'Gamma' (midtone values) range and even somewhat into the 'Gain' (higher values) range, it means that changes are smooth and blended. For most global changes (like those we have made so far), that's exactly what we want. 

This illustration shows how the Primary Wheels tools work:
But the Primary Wheels tools are not the only tools for manipulating color and tone in Resolve and several of the others are quite different.  At this point in on this shot we need more precise tools, which are available in Resolve in Curves and in the LOG menu. 

[There are others, too, but we'll leave those for another day ...]

Let's say that our objective in working with this specific frame is to separate the lower values and get both rich black and tonal separation in the black T Shirt of the man facing us. We want that shirt to be as pretty as we can make it. Let's look at how we might do that using Curves.


__________________________

Y (Luminosity) Curves

The Curves menu looks like this:



By default, the YRGB curves are all active and linked when the Curves menu is selected. By clicking either one of the YRGB buttons at the upper right or the Anchor Icon to the left of them, however, they can be individually selected. 

We want the Y Curve. This curve represents the 'Luminosity' channel and changes only tonality/contrast. This is a very important tool in Resolve because with it, the colorist can change global or local contrast relationships without increasing color saturation. We're going to add points on the curve and change contrast in the lower end of the value scale to bring out the folds in the black T Shirt.



Overall we have deepened the black of the shirt but through the single point raised above the curve we are separating the tones of the folds to make them stand out.






Although it is possible, as shown, to target very specific tonal ranges using Curves, we're still constrained somewhat by the curve itself. Notice that not only were the very lowest ranges affected by the change but so also were others. Curves give you more control than the Primary Wheels, but still not precisely targeted controls.


__________________________

LOG Menu

Let's look at the LOG menu.


logmenu.png


Although it looks very similar to the Primary Wheels menu, instead of LGG (Lift, Gamma, Gain), the LOG menu has Shadow, Midtone and Highlight. It’s not just the labels that are different, they operate in a very different way, as shown by the following illustration:




The Log menu tools have very little overlap, so it’s possible to control Shadows with very little effect on Midtones or Highlights. Let’s return to our last waveform:




We have now stretched out the value range so there is clear separation between the lower values of the waveform (corresponding, roughly, to Zones 0 - 3). We'll use the LOG Menu to work with those precisely.  My next move will be to use the Shadow control in the LOG menu to drop the lowest values in the waveform to pure black. You’ll note that there is very little change in the overall waveform, only the dropping of the lowest values.








Here’s how it looks with saturation back up to normal:




__________________________

Final Tweaks

Although we now have good values in the lowest blacks, and clear separation in the lower Zones, the image still seems a little washed out so we'll return to the Primary Wheels menu, taking advantage of the smoothly blended changes, and tweak it a little bit.







With normal saturation:


Compared to our ungraded image, you’ll see we were able to bring in a full tonal scale - crushing only the blacks we wanted to take to full black - without sacrificing any shadow detail or making the image oppressively dark.



Original, ungraded image:





Happy Grading!



No comments:

Post a Comment