(continued from DV and DVD Black Levels Part 2)
Note: If you need more info on the basics of DVD burning, take a look at our DVD burning instructional video.
Proc amps
Until not too long ago proc amps were quite expensive and required use of a waveform monitor in order to set the levels. As noted above, Sign Video now makes an affordable proc amp that includes a calibrated meter so you can easily, and accurately, set the black level.
We should mention that even if you use a proc amp you still want to be sure to calibrate your video monitor. A lot of video producers use TV's with monitor inputs. If you do that, be sure you do not enable any of the TV's options that are designed to "enhance" the picture. You should also use colorbars to adjust the monitor.
Okay, so you've calibrated your monitor, used a proc amp or DV/DVCAM player with 7.5 IRE analog output, but your DVD's still look different than the DV tape source. What now?
Your MPEG2 encoder and black levels
Well, it's now time to take a look at your MPEG2 encoder. The differences
between various MPEG2 encoders are often fairly obvious when it comes to
things like pixelization (blocky artifacts), but not so obvious when it comes
to preservation of black levels and color values (luma and chroma). However,
once you have established that your system for monitoring video is correct,
you will then be able to tell if your MPEG2 encoder is changing the luma
and chroma values. Some of the early releases of MPEG2 encoders for desktop
DVD production made significant changes in luma values. Some newer ones also
change the black levels, but not as much and with some types of source video
you may not notice it at all.
You may also notice an apparent difference in levels because of the loss of detail after your video is encoded to MPEG2. Take another look at the ship in the water: in the DVD screenshot there is less contrast in the ripples in the water. which makes it look a little bit lighter than even the corrected camcorder analog output. Using a better MPEG2 encoder and/or a higher MPEG2 bit rate can help retain some of that lost detail and contrast.
Depending upon the kind of videos you produce, you may decide that if there is a change in luminance levels caused by the encoder, it is something you and your clients can live with. For other, more critical work, you might want to acquire one of the MPEG2 encoders that do not change the values (for Macintosh and Windows users, you can find an excellent MPEG2 encoder starting at under $60 US).
If you do get a proc amp, do get a better MPEG2 encoder AND STILL something seems wrong, what then? Then it's time to take a look at how you shoot video and/or capture video.
Correct levels for shooting and capture
Some experts say that the auto exposure on most camcorders will routinely
overexpose the image, so your videos may end up being lighter than you would
like. I often let the auto exposure read a scene, then switch to manual exposure
mode and set it to be one step or so darker than the auto exposure reading.
You cannot really trust your camcorder's LCD monitor while shooting, and
even if you plug an external NTSC monitor into the monitor while shooting,
you will still have the problem of the DV camcorder outputting the wrong
level for North American NTSC monitors.
Analog to digital video conversion
Converting analog video to digital video is another process that can cause
problems. If you are capturing video from NTSC analog sources including
VHS, S-VHS, Hi 8, 3/4" U-matic, etc. you may end up with incorrect black
levels. Those kinds of analog video equipment output 7.5 IRE but if you
plug them into the analog inputs of a DV camcorder/VCR or one of the standalone
analog-to-digital converter boxes you may need to use a proc amp to change
the analog output to 0 IRE. If you don't change the levels during conversion
from analog to digital, then your DVD's may end up looking very washed
out. If you have a video capture card installed in your computer you may
want to check with the manufacturer to find out if the card expects input
levels of 0 IRE or 7.5 IRE. Some cards are switchable.
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Authoring DVD or How to Burn a DVD and Not Get Burned
How to Calculate Bit Rates for DVD Production
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© 2004 by Sign Video Ltd.