HDV color correction

[Mike Gannon]

In looking at an HDV NLE setup, would one have to use a professional HD CRT monitor for color correction or are the new 1920x1200 LCD displays up to the task? Is downconverting to an SD CRT broadcast monitor an option?

[Douglas Spotted Eagle]

Downconverting isn't an option. On the other hand, the 1900 x 1200 monitors are a viable inexpensive (sorta) solution. Viewers of HD will be viewing on LCD or plasma monitors, and so you'll be very, very close using the LCD. That's what I'm currently doing with Vegas, and it works fine, based on what I'm seeing. I have access to an HDV CRT, and check my test footage there regularly, I'm now getting to the point that I've got confidence in my LCD. Not optimum, but first, I don't have space for an HD monitor, and second, we're not delivering enough to HD yet to justify the cost.
But, with Blu-Ray around the corner....HD delivery isn't far behind.

[David Newman]

Technically it is possible to color correct with a calibrated SD CRT, but they are issues. The main issue is SD is using ITU.BT601 color space and HD is ITU.BT709. These are difference YUV color spaces. You can't drive a SD monitor with any YUV based signal (composite, Y/C or component YUV) without taking this into account. Also you can't use RGB component without knowing what YUV to RGB conversion math has been applied in the NLE or output card. Basically to solve all this your NLE must be able to do 709 to 601 colorspace conversion when needed. This was one of the big additions we had to make to Aspect HD (v2.5) when supporting the Sony HDV camera (Sony uses 709 whereas the JVC camera is 601.)

Note: with the JVC HDV camera, technically you got a better color match using SD monitor rather than HD because of its native colorspace. Generate colorbars in the camera a you will see what I mean.

Sadly most of today's video tools are only 601 aware -- this includes most of the graphics cards that have SD/HD outputs. So when we play 709 video to a 601 device we do the conversion math on the fly. We do this so you can color correct using inexpensive SD broadcast monitor -- also you can uses SD vectorscopes. 709 and 601 issues have not yet become common knownledge, but this is one of the hurdles for switching from SD to HD production.

[Mike Gannon]

Thanks very much for your suggestions. What about a CRT HDTV? They have really come down in price - Crutchfield has a 27" Toshiba in native 1080i for $700 - but it does not have firewire, only component, S video and HDMI.

Anyone want to chime in on this as a low-cost solution?

[David Newman]

It is always good to have a consumer screen reference, but these monitors are not calibrated for the purpose of color corrections. Consumer monitor are always pushed so that they stand out on a showroom floor -- more contasty and saturated than they show be. I guess it is possible to tweak the settings for better calibration. Certainly cheaper than a Sony PVM20L5 HD (lowest end HD refernece monitor.)

[Josef Crow]

David

so Aspect does 709 to 601 conversion on the fly. Does this mean i can still color correct with Aspect using an SD monitor, or would it be better (resolution issues aside) with an HD monitor?

thanks

[David Newman]

You can color correct with an SD monitor. Resolution aside there is no additonal advantage to an HD reference monitor when using Aspect HD 2.5 (now in a public beta.)

[Kevin Shaw]

David: what if you want to view your timeline output on an HDTV monitor? Is there a way to tell Aspect HD which color space to use for the output display?

Also, is there an easy way to send the output to an HDTV using a standard DVI video card or other stock hardware? How would you configure your editing software to send a full-screen signal to the HDTV?

[David Newman]

We currently allow the user to select 709 or 601 modes. The behavior currently assumes the hardware is not 709 aware (as so much is not), so the 709 opinion add an RT 709 to 601 filter to the output upon playback. If you do have 709 hardware, switch this off, and the YUV will be unchanged.

Preview options are many as most good video cards have dual head DVI or some even component Y,Pr,Pb. At DV Expo the new Maxtox Parhelia has component HD out (they were demoing it with Aspect HD.) It will retail for $350.

[Rob Lohman]

David: that's very interesting and informative, thank you! Do you
happen to have a link that clearly describes what the differences
are between these two color spaces? I never really knew that this
existed, so it would be great to read up on the technical side of it.

Thanks!

[David Newman]

I don't have a simple link that explains only ITU.BT.601 and ITU.BT.709 color standards. Everything a could find is deep in color science (for good reasons) like this Charles Poynton paper http://www.poynton.com/papers/Guided_tour/abstract.html.

Very simply every color space describes a subset of all possible colors (viewable or not), in HD a new range of possible colors (color space) was adopted to more closely much the display devices being used. This is way over simplified but the rough idea.