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Confusion on getting proper color on MPEG2 output for DVD

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Chris Blair
Confusion on getting proper color on MPEG2 output for DVD
on Apr 21, 2009 at 2:15:26 am

I posted this in the compression forum and thought this might be a good place to post as well.

We use several Harris VelocityQ editing systems for day to day editing. We typically output DVDs for clients by just playing out to Panasonic DVD recorders with excellent results.

When we need menu based DVDs, for years we've encoded out of the Velocity systems using their MPEG2 export, which uses the Ligos codec. That codec is getting rather long in the tooth...and while it looks OK, we're looking to improve the quality of our MPEG2/DVD output.

That brings me to the question. When using the Ligos encoder from our NLE systems, we actually have to expand the colorspace by increasing video and saturation by about 8%, and decreasing blacks by roughly 10%. Years ago we actually output a series of MPEG color bars from the edit system, then compared them side by side on a waveform/vectorscope before settling on the adjustments.

We're testing Carbon Coder to encode the MPEG2 files (from uncompressed AVI's, with color bars that are right on the money on a waveform/vectorscope). In Carbon Coder, we're finding that we have to add the 601 shrink filter, along with a very slight contrast boost to get an exact color match on the MPEG2 files (these are compared with the original video side by side with a waveform/vectorscope).

My question is...why the huge difference in codecs? Why do we essentially have to expand the colorspace using the older Ligos codec, but shrink the color space when using the newer Main Concept codec that Carbon Coder uses?

Ultimately, it doesn't matter, but I'd like to be able to explain it to our other editors if it has an explanation. My assumption is that the two codecs operate in different colorspaces??

Thanks for any help on this.

Chris Blair
Magnetic Image, Inc.
Evansville, IN

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