There's a lot of mystery surrounding
the four gamma settings available on the Panasonic DVX-100 miniDV
camcorder. The options are "NORMAL", "LOW",
"HIGH", and the intriguing "CINE" setting
which is hyped as more "filmic". Stymied myself with
what these options actually offer, I set out upon a scientific
approach to gain a better understanding of how these various
gammas affect the camera and its images.
I set up my DVX-100 on a tripod square to a DSC Labs 11-step Front Box chip chart and
ran a firewire cable from the camera to Final Cut Pro on my iBook.
I used the waveform monitor available in FCP's "Log and
Capture" mode to insure the chart was evenly lit and to
analyze the luminance levels being read by the camera.
Using the camera's linear CINE gamma setting (more about that
in a sec...) and the waveform monitor, I optimized the latitude
of the camera by exposing the white chips on the chart to read
right around 100 IRE. I then dialed down the camera's MASTER
PEDESTAL to -9, the point at which the blacks hit 0 IRE without
crushing. The result and the standard to which I measured the
other three gamma settings is shown below...
Rather than employing any sort of curve/compression in the toe
(shadow region) or shoulder/knee (highlight region) which is
what you find naturally in film and electronically in video to
better manage the rapidly diminishing detail on either end of
the spectrum, CINE gamma provides a linear response to the camera's
You can see this on the chart as the progression of chip luminance
values appears to increase/decrease in equal amounts and this
can be verified by the adjacent waveform reading that displays
fairly evenly spaced luminance values with the crossover (the
middle gray chip shared as a common value between the upper and
lower row of chips) just a smidge higher than 50 IRE or true
With NORMAL gamma you'll notice right away that the highlights
in the chart get a whole lot more highlightier (a very non-technical
term that I just made up on the fly). In the CINE chart, there's
a very clear separation between the two brightest chips whereas
with this NORMAL chart, the chips come very close to blending
together. The chart appears brighter overall and while the pure
black still seems pretty black, it looks as if though the shadow
region begins to stretch up to higher values.
Looking at the waveform monitor, we can analytically verify what
we're seeing with our eyes. I sampled the two brightest chips
in the CINE chart right around 96 and 87 IRE. In this NORMAL
chart these two values come in at 99 and 96. You can also see
that the values begin to compress, an indication of decreasing
detail. The crossover bumped up approximately 10 IRE, compressing
and reducing contrast in the upper gamma and highlight region,
stretching out and increasing contrast in the lower gamma and
shadow region, and resulting in an overall brighter image.
It's hard to tell what LOW gamma does. The chart and waveform
monitor look very similar to NORMAL. The values I sampled are
almost identical in the highlight and shadow regions while the
most significant change, which isn't saying much, is in the mid
gamma. The greatest difference is in the crossover point which
is lower by roughly 5 IRE.
Again, it's hard to tell what's going on with the HIGH gamma
setting. The waveform monitor indicates common crossover and
highlight values. The difference both in the waveform monitor
and in the values I sampled indicate a stretching up of the lower
gamma and shadow region, but only by a few IRE.
This is the chart I plotted based on pixel sampling from the
video captured chip chart. Nearly common values are shared in
the shadow region and then the separation between CINE gamma
and the other three very similar gammas begins.
* Check out my article on "Over/Underexposing Video"
Copyright ©2003. Dan
This article was originally
published at DanCoplan.com
and is reprinted here with permission.
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