|Tutorial: The Range Check Tool in Final Cut Pro 3
Range Check Tool in Final Cut Pro 3
Luma and Chroma Ranges
By Ken Stone
Watching a little
TV the other night, a local commercial came on. Halfway through
the commercial a bright red telephone number came on screen.
Too hot for broadcast. The red color of the phone number was
smeared across the screen and the audio screeched, making me
dive for cover. Obviously the commercial was not done using Final
Cut Pro 3. (grin)
So what does Broadcast Safe mean?
Here is a simple answer. Due to the physical nature of television
broadcasting, there are limits to both the luminance (brightness)
and chrominance (color saturation) of the video that that is
acceptable for broadcast. If the luma, chroma or both levels
exceed these standards then problems will occur at the receiving
end of the broadcast, on TV sets at home. Problems like smeared
color, blown out highlights and bad audio. The audio itself might
be at the correct level but when the standards for luma or chroma
are exceeded it tends to ruin the audio as well. Different broadcast
facilities have different standards so unfortunately there is
no one fixed standard for the industry. If there is a 'defacto'
standard it would be the Corporation for Public Boardcasting
guidelines. Each broadcast facility makes guidelines available,
of what is for them, a legal video signal.
We have had the ability to set
Luma and Chroma levels for 'Broadcast Safe' in versions prior
to FCP 3, using the Waveform and Vector scopes in conjunction
with color correcting filters. We now have a new tool that make
the process much easier. The Range Check tool.
Range Check Tool
The Range Check tool offers three different
modes for testing for illegal broadcast levels; Luma, Chroma
or both. Range Check is selected from the View menu and can be
used in both the Viewer and Canvas window, depending on which
one is active at the time of selection. Range Check only looks
at the frame that the Playhead is parked on and does not run
in real time.
When Range Check is enabled you will
always have an icon on screen.
- If levels are within standards there
will be a black check mark in a green circle.
- A black check mark, green circle with
an arrow point upwards, denoting that Luma is within range but
some of it is between 90% and 100%, this is a caution.
- A yellow triangle with a black exclamation
point shows that you are out of range.
With the Range Check tool set to Luma
(brightness), there will be green moving zebra strips over areas
that are 90% to 100% luminance (cautionary), red moving zebra
stripes for luminance of over 100% and out of range. With Chroma
(color saturation) selected there will be red moving zebra stripes
for areas over 100%. There are no green zebra stripes (as caution)
with the Chroma Range check. When Range Check is set to 'Both',
there will only be red zebra stripes showing out of range. No
way of knowing which is out, Luma or Chroma. Despite the fact
that Luma has the green zebra strips when in Luma mode, when
set to both, the green zebra strips are not available.
Luma Range Check - shows
green zebra strips
(green arrows) for those areas of luminance between 90%
and 100%. Red zebra strips (red arrows) shows luminance over
Chroma Range Check - shows
red zebra stripes
(red arrows) for those areas of chromance over 100%. No green
cautionary green zebra stripes available with the Chroma Range
Range Check Both - Combines
the red zebra stripes
of both Chroma and Luma. The green zebra stripes from
the Luma Range Check are gone.
The Range Check tool is helpful in spot
checking the Luma and Chroma values of your video footage. You
will need to place the playhead on any frames of video that you
want to check. This tool is also useful when doing color correcting.
Turn on Range Check while color correcting to insure that your
color adjustments don't push you over the top. The Luma Check
is helpful in that it shows those areas of luminance that fall
between 90% and 100% as well as areas that are too hot. I wish
that there was an on screen marker telling us which Range Check
is in use, Luma or Chroma. I often forget which one I am using.
If you see green zebra strips you will know that it's Luma that
you are using.
I have found having the green zebra strips
of the Luma Check is very helpful for adjusting white levels
and highlights (brightness and contrast). At the same time, I
need to see my Chroma values as well. Range Check - 'Both' does
not employ the cautionary green zebra stripes of the Luma Check
and when red zebra stripes are displayed there is no way of knowing
if it's Luma or Chroma that's out of range. There is a workaround.
Make your Viewer active and select Range Check Luma, now make
your Canvas active and select Range Check Chroma. This way you
can have a check of both Luma and Chroma but in separate windows.
You can have Range Check on when working in FCP but be sure to
turn it off when laying off to tape or exporting to QuickTime.
The Range Check tool would be even more
helpful if it employed a feature found in the Audio Peak Detection
tool. 'Mark Audio Peaks' can check an entire Sequence and place
markers where audio volume exceeds 0 dBs. We need a 'Mark Luma
and Chroma Peaks' option that would cause FCP to scan an entire
Sequence and place markers where our Luma and Chroma values exceed
the legal broadcast range. Well, maybe in FCP 4.
copyright © www.kenstone.net 2002
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