FORUMS: list search recent posts

Confusion on getting proper color on MPEG2 output for DVD

COW Forums : Compression Techniques

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
Chris Blair
Confusion on getting proper color on MPEG2 output for DVD
on Apr 21, 2009 at 1:45:30 am

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 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
http://www.videomi.com


Return to posts index

Daniel Low
Re: Confusion on getting proper color on MPEG2 output for DVD
on Apr 21, 2009 at 10:23:29 am

The MainConcept codec should be bang on, you shouldn't need to apply any colour correction to it. I can understand needing to adjust the Ligos codec, the underlying code for it is over 17 years old.

__________________________________________________________________
Two years from now, spam will be solved. - Bill Gates, World Economic Forum 2004


Return to posts index

Chris Blair
Re: Confusion on getting proper color on MPEG2 output for DVD
on Apr 21, 2009 at 1:12:06 pm

Interesting because that's what I read in researching this as well...but what we're seeing doesn't support it.

The original file is an uncompressed AVI captured into a Blackmagic Decklink HD Extreme whose color bars and video read perfectly across multiple waveform/vectorscopes (actual hardware devices...not the software kind). But the resulting MPEG2 file from Carbon Coder (without any filters) comes out with black levels near 0 ire, and video levels about 10% higher than they should be. Obviously, the video looks pretty bad that way.

Applying the 601 shrink filter gets the color bars back close to where they should be, but the mid-levels are all a little low (compared to the original), and black levels are a tad high...so adding a slight contrast boost gets everything very close to the original.

We've done multiple tests with this too. Outputting an uncompressed AVI via export from our VelocityQ (it too looks perfect on the waveform/vectorscopes) as well playing the timeline out through SDI into the Blackmagic Decklink device in real-time. The two files (software encoded and real-time hardware captured) are virtually identical, so there's nothing wrong with the source.

We've also used mutliple DVD exports out of Carbon Coder. So from what we're seeing, either something isn't right with the Main Concept codec, or in how Coder implements it. Again...not a huge deal as we've figured out how to get everything looking good, but very frustrating and time-consuming to have to spend all that extra time and energy to "fix" something that's not supposed to need fixing.

Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com


Return to posts index


Daniel Low
Re: Confusion on getting proper color on MPEG2 output for DVD
on Apr 21, 2009 at 1:21:03 pm

[Chris Blair] "uncompressed AVI captured into a Blackmagic Decklink HD Extreme"

YUV or RGB?



__________________________________________________________________
Two years from now, spam will be solved. - Bill Gates, World Economic Forum 2004


Return to posts index

Chris Blair
Re: Confusion on getting proper color on MPEG2 output for DVD
on Apr 21, 2009 at 3:51:45 pm

I'll have to check. That system is tied up on a project at the moment. I picked the Blackmagic uncompressed 10bit option but didn't notice which colorspace it used or even if it specified one. I thought it was YUV but will get back to you.

Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com


Return to posts index

Chris Blair
Re: Confusion on getting proper color on MPEG2 output for DVD
on Apr 21, 2009 at 4:14:10 pm

It's Blackmagic 10bit YUV uncompressed. It reads perfectly on both a software waveform (Adobe On Location) as well as coming out of the Blackmagic's component output to a hardware based waveform.







Chris Blair
Magnetic Image, Inc.
Evansville, IN
http://www.videomi.com


Return to posts index


Daniel Low
Re: Confusion on getting proper color on MPEG2 output for DVD
on Apr 21, 2009 at 10:35:24 pm

One for Rhozet/Mainconcept support....

__________________________________________________________________
Two years from now, spam will be solved. - Bill Gates, World Economic Forum 2004


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2017 CreativeCOW.net All Rights Reserved
[TOP]