Those of you who know my love of detail ought to get a chuckle out of this one, for I will regale you with a tale that begins, simply, with an explanation of the workings of one of DaVinci Resolve’s reset buttons, and ends with an explanation of the difference between the two different ways you can adjust luma contrast in Resolve.
However, let’s start with a look at the RGB reset button, specifically, found on either the Wave or DaVinci control surfaces (I’m not picking favorites, those are the only two that are compatible with Resolve at the moment).
Trust me, this is going to get interesting.
I’ll speak to current and future owners of the Tangent Wave panel first, as I suspect there are rather more of you out there. There are two reset buttons found next to each trackball/contrast dial pairing for lift, gamma, and gain. The top button (circle) resets both color balance and contrast to the détente position (a value of 0 for the Y’, R, G, and B channels).
Meanwhile, the bottom button (dot) resets only the R, G, and B channels. This arrangement is different then for Color, where one button resets RGB only, and the other resets Y’ only, but that’s the way it is with learning new software, something’s always different.
Simple, end of post, right? Well, let’s take a look at a straightforward series of corrections, and examine what happens when we actually use that RGB reset button. Here’s the original image:
In the following image, I’ve expanded contrast by raising the gain and lowering the lift controls using the dials on the Wave control surface to create an image with excessive contrast.
Next, I’ll make a ham-fisted adjustment so the highlights of the image are really, really blue.
Coming to my senses, I decide that the blue adjustment is actually ridiculous, but I still like the expanded contrast, so I press the RGB reset button (dot) corresponding to the gain controls on my Wave panel to reset the color but not the contrast.
The result is an image that’s now less saturated then it was in shot #2, before I made the blue adjustment. What gives?
The answer to that just happens to dovetail with one of the things I really like about DaVinci Resolve, which is that there are actually two very different ways you can adjust image contrast, depending on your goals.
The first set of controls are the three large dials on the Wave (or rings on the DaVinci surface) that adjust contrast by raising and lowering Y’RGB all together, which you can see if you look at the indicator bars on the interface.
Using these, expanding contrast also raises image saturation, and compressing or lowering contrast results in lowered saturation.
These controls are great for making bold changes to color and contrast all together, and for expanding flatly shot images into their full glory without needing to also raise saturation.
ADDITION—It’s been pointed out to me that middle-clicking and dragging up and down within any Y’RGB slider group for Lift, Gamma, or Gain will uniformly raise or lower Y’RGB as if you’d used the control surface dials.
However, in the second page of commands for the knobs and buttons along the top of the Wave (or via a dedicated set of three knobs on the DaVinci surface) there’s a second set of Lift/Gamma/Gain controls that let you adjust the Y’ channel independently of the RGB color components.
Using these, expanding contrast does nothing to numerically alter image saturation, but saturation diminishes perceptually relative to the change we’re making to the Y’ channel. Conversely, compressing or lowering contrast with these controls appears to raise saturation. The effect is the same as if you used the Y’ vertical sliders and Lum Gain/Gamma/Lift horizontal sliders both adjust only Y’.
These controls are great for altering shadow density, for getting punchier blacks without changing the color too much, or for fixing specific broadcast legalization issues.
I really like having access to both kinds of contrast controls, and use both regularly for different situations. This is also the key to understanding what’s happening when we use the RGB reset button. Looking at the Primary bars UI for Lift/Gamma/Gain of the original, unaltered image, we see:
When we raise highlights, Y’RGB all go up together.
When we then alter the color balance towards blue, the R channel diminishes while the B channel increases and Y’ remains unaltered.
When we reset RGB, the R, G, and B channels all go to 0, while the Y’ channel remains elevated where it was.
This is why saturation diminishes, because the net result is that you’ve raised Y’ independently of RGB.
So now you understand the default behavior of the RGB reset button, you can determine when its functionality best suits your needs, and as an added bonus you got a window into the dual sets of contrast controls that Resolve makes available to you.
Special thanks to Director Jake Cashill for clips from Oral Fixation.
9/27/10—Added a correction about the ability to adjust Y’RGB by middle-clicking and dragging onscreen Lift/Gamma/Gain sliders.
11/14/10—Added to the preamble of the article.