[This article is a follow-on to a training video I created about reading scopes in Premiere Pro CS6. You can view that video here. I just realized I haven’t written about the Three-Way Color Corrector filter in Premiere. I will remedy that in the next few weeks.]
Now that we know how to read scopes, there’s still a basic problem: today’s digital cameras shoot video that is fine for the web, but the white levels they record are too hot for broadcast, cable, or DVD.
In addition, programs like Photoshop allow us to create colors that are fine for the web, but excessively over-saturated for broadcast, cable, or DVD.
Adobe Premiere Pro CS6 provides a tool to help us solve the double-problem of excessive white levels and over-saturated chroma levels. It’s called the “Broadcast Colors” filter.
BUT FIRST, SOME BACKGROUND
(Image courtesy of Google.)
The predecessors of today’s cameras were analog video cameras. These units recorded video on tape, rather than cards or hard disks. And the limitations of the entire video system were such that video levels could not exceed 100%, as measured on the Waveform Monitor, without causing trouble.
Those maximum levels were “baked into” the technical limits of video tape, broadcast, cable, and DVDs. White levels that exceeded 100% would do very bad things, including causing a picture to break-up, inject hum into the audio, cause a cable headend to shatter the video image into small rectangles, even knock a broadcast transmitter off frequency.
Just as white levels had limits, so, too, did saturation. The computer is easily capable of creating saturated colors that far exceed the chroma limits imposed by video.
None of these problems make video engineers happy.
Now, if you create and post video exclusively for the web, you don’t really need to worry about this, because the web is very forgiving and can easily accept these excessive levels. However, if you plan to create any projects for broadcast, cable, or DVD, you need to care a great deal, because submitting a program that doesn’t take these limits into account will get your program rejected by the “engineering-powers-that-be.”
HOW TO SPOT THE PROBLEM
White levels that are too “hot,” or exceed safe levels, are indicated on the Waveform Monitor with a trace that goes over 100%. In this screen shot, the 100% white level line is the third yellow line down from the top, and three peaks in excess of that are indicated by the red arrows.
Chroma levels that are too saturated are, in general, any levels that exceed a bounding rectangle connecting the tops of the color targets on the Vectorscope. Starting in the top left and rotating to the right, the colors are: Red, Magenta, Blue, Cyan, Green, Yellow and back to Red.
NOTE: These targets shift position when you switch between NTSC, PAL, and HD. (Why should this be easy?)
In this screen shot, the top arrow points to an over-saturated red, while the bottom arrow point to where pure gray (i.e. no color saturation at all) is located.
NOTE: The issue of over-saturated chroma (or colors) is made even more complex in that mid-tone values can carry a lot more saturation than colors that approach white or black. The Vectorscope may show a color which is safe, when, in reality, it isn’t.
Think about this circle. Gray-scale is represented by a vertical line going from bottom to top. Saturation is represented by distance out from this center line. (In my classes, I describe this circle as a grapefruit — it makes for a better story.) There is a lot more room for saturation at the equator, than at the North or South pole.
HOW TO FIX THE PROBLEM
The Broadcast Colors filter (in the Color Correction folder) allows you to quickly fix problems with white levels or over-saturated chroma. Here’s an example.
This is a gradient that shades from pure white, on the left, to pure black on the right. Every shade of gray is represented in that gradient which totally fills the screen.
Here’s what that gradient looks like on the Waveform Monitor. It shades smoothly from 100% white, on the left, to 0% white (black) on the right.
Here is a simulation of that gradient shot using a current video camera. Note how the white levels exceed 100%. This is typical of almost all video cameras, they record excessive white levels.
Normally, we use the Three-Way Color Corrector filter to adjust highlights so that they don’t exceed 100%. As you can see here, I’ve lowered the entire angle of the gradient (by adjusting the output level) so that white levels max out around 90%. This adjusts every gray-scale value in the image proportionately.
Using the Three-Way Color Corrector filter is, generally, the best option because it preserves all the highlight detail (think lace on a wedding dress). However, sometimes, you don’t care about the detail in the highlights; for example, when they are caused by an over-exposed window, or the heart of a candle flame.
We can apply the Broadcast Colors filter which “clamps,” or restricts, just the white levels, without also adjusting mid-tones or black levels. Notice, here, the flat line exactly at 100%. The filter has lowered all levels above 100% to exactly 100%.
The good news is this works great. The bad news is that it smushes the highlight details into a bright blob. Again, with a blown-out window, I don’t care. With the delicate lace details in a wedding dress, I care a LOT, because all that detail disappears when the Broadcast Colors filter is applied.
NOTE: The point I’m making is that sometimes, adjusting clips with the Three-Way Color Corrector filter is the best option, and other times using the Broadcast Colors filter is a better choice. There’s no one perfect answer.
Here’s another example, this time with chroma. Our earlier example of excessive reds has now been reduced, using the Broadcast Colors filter, so that the colors are “safe.”
NOTE: The closer your gray scale values get to 100%, or 0%, the less saturated your colors are allowed to be.
TO APPLY THE FILTER
To apply the filter to a single clip, select the clip and double-click the Broadcast Colors filter; it is in the Color Correction folder.
To apply the filter to a range of clips, create an adjustment layer that covers the clips to want to adjust – normally, this is your entire project – and apply the Broadcast Colors filter to the adjustment layer.
VERY IMPORTANT POINT: In order for the Broadcast Colors filter to protect against excessive gray-scale or chroma levels, it must always be applied after all other filters are applied, or in the top-most adjustment layer.
For web video, the Broadcast Colors filter is nice, but not necessary. For anything else, it is essential.
When you care about highlights, correct the clip using the Three-Way Color Corrector.
When you don’t care about highlights, the Broadcast Colors filter is a very fast way to keep all of your clips color safe.
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