This thread follows along from VPX Color Space thread, and discusses adjusting for luminance levels, or what most would term as brightness levels.
I would like to know how others do this, particularly for changing light conditions over the duration of a video clip.
In VPX11, I have set up my template for:
- Effects/Movie Settings (Master effects) - Color Space Correction turned on (to limit levels to between 7.5 and 100)
- Waveform Monitor Display 7.5 IRE Black checked so that 7.5 and 100 show up
- Project Settings/Movie Settings Color Space set to BT.709
I will not go into White Balance, which seems to have its own set of difficulties.
There are several ways to make adjustments to the luminance levels, which is usually the first thing to do for colour correction:
- Auto Exposure
- Auto Color which does an Auto Exposure at the same time
- Adjust the top and bottom points of RGB curve to bring the blacks and brights to within the legal limit, or reduce them to the legal limit
- Raise (or lower) Gamma to bring the brights to near the limit.
What not to use: Brightness!
There are a few problems. The first problem is that of selecting a frame to apply the adjustment, the second problem is keyframing. Auto Exposure, Auto Color/Auto Exposure are applied to the current frame and cannot be keyframed. Adjustments to the RGB curve cannot be keyframed. Thus, selection of the frame is important. Combining Auto Exposure or Auto Color/Auto Exposure with an adjustment to the RGB curve can cause problems as they could be cumulative.
RGB Curve Adjustments:
In the image below, this frame has the brightest level of the clip, i.e., the highest point in the Waveform Display, at just over 90.
The frame in the image below is at about the lowest upper level of the clip, at just under 70.
The idea behind Luminance Level Adjustment is to get the brightest points up to almost 100, unless one
wants something else.
If one uses this last frame and brings up the top of the RGB curve by dragging it to the left so that the brightest part is just below 100 (X=170.3), gives:
However, moving to the brightest part of the clip, the brights are now crushed against the 100 level. Compare this to the waveform in the first image.
Thus, one should look for the brightest part and make the adjustment there. Here are the before and after adjustments:
Before (RGB reset):
After (adjustment of top of RGB curve to X=237.4):
However, going back to the darkest part (at 2:08), this part could use some lift. Keyframing is required.
So what to do?
For anyone following this who is using MEP and does not have the Waveform and other instruments, what not to do is raise the brightness. Doing so moves the entire waveform upwards. Below is the result of raising Brightness to 86. The top moves up, but the darker parts move up and closer to the brighter part, reducing the dynamic range. Terrible result.
Thus, use Gamma. I reset Brightness and raised Gamma to 74. This brings the brights up, but leaves the darker parts at the bottom and stretches the shades in between.
This is almost as good as raising the RGB curve to about X=170.3:
However, a little bit of the definition seems to be lost. Increasing Contrast to about 53 or 54 may help.
Below with the RGB curve at X=237.4 (set for the brightest frame) and keyframing gamma gives fairly constant luminance for the entire clip:
Note that trying gamma high or mid does not have the same effect and is actually worse.
IMPACT OF USING AUTO EXPOSURE:
If the RGB curve has been modified, as I did setting the top point to X=237.4, clicking on Auto Exposure will crush the brights up at the top:
Reset RGB curve, turn on Auto Exposure gives (at the location of the brightest part of the clip):
Below is the waveform at the darkest location. Auto exposure only raises this slightly, similar to raising the RGB curve to X=237.4, thus keyframing Gamma will still be required:
Of course, applying Auto Exposure at this point would blow out the brights for the rest of the clip.
Conclusion: With a clip that changes exposure (upper brightness level) over time, try first Auto Exposure or Auto Color, then make adjustments using Gamma and a slight amount of Contrast, if necessary.
Alternatively, at the brightest frame, adjust the upper level of the RGB curve to bring the brightest part close to 100, 95 is probably best to avoid blowing out any brights.
Q1: Is this what others do?
Q2: Is there some other way?
MEP ONLY: Movie Edit Pro 2019 Plus/Premium does not have the colour curves. Strange, because PhotoStory Premium 2019 does.
Q3: Does MEP 2020 have the Color curves?
Alternative solution (especially for MEPP): Use New Blue ColorFast 2 if you have it. It contains scopes, like the Waveform monitor.