Behind the Orange Curtain

In this week’s post I have decided to address some very technical, often confusing and even more often misunderstood concepts in digital video; color space, chroma sub-sampling and gamma.  (see I told you it would be techie)  These concepts have become more important to understand recently in light of the new “digital cinema” cameras like the RED, SI-2K and the new Varicam that have brought “film-like” workflows into the television world.  The fact is that these cameras can capture much more than our current HDTV systems can display.  The challenge then for those doing high-end production work is how to retain as much data as possible through the post-production process so that we can maximize the look of the final product.

Color space refers to how color values are represented.  In the television world (which is the only one that I will address here), there are two options, RGB or YUV.  RGB is found in high-end formats like HDCAMSR and YUV is found in most others.  RGB is the purest form of representation but requires the most data to store.  YUV allows for greater compression, which is why it tends to be so popular in the digital video world.

Chroma sub-sampling has to do with how much chroma information is lost relative to the luminance information when recording in compressed formats.  In 4:4:4, everything is given equal weight, whether in YUV or RGB.  In 4:2:2, 4:2:0 or 4:1:1 the amount of chroma information sampled is less.  Here is a diagram that may help you understand what I am saying.

HDCAMSR is one of the few formats that will allow recording in RGB color space with 4:4:4 chroma sampling.  If your budget allows, this is the best quality path to go down.  A competent post house that is up to speed with RED and SI-2K workflows can convert these cameras files to HDCAMSR in 4:4:4 for high quality mastering.

Lastly, is gamma.  Gamma curves are applied to video signals to allow the captured content to be properly displayed on various monitors.  The problem with this in recording formats is that applying a gamma curve to the image before recording does not always preserve the maximum amount of information throughout the post-production process.  These newest cameras can all acquire in either a RAW or logarithmic format (like Panasonic’s Film Rec gamma), which will look very odd on a monitor, but allows the maximum amount of dynamic range in the recording.  Use of one of these types of gamma requires that a look up table (LUT) be applied to the output when doing final color correction.  This is a normal part of the workflow if you are using products like Autodesk’s Smoke and Fire or Apple’s Color.  It is often difficult for many to understand why the image looks “bad and washed out” through the offline process, but the end results are worth it.

This is only a very cursory look at these concepts.  If you would like more information or have additional questions, feel free to contact me through Post Factory.

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This week we are back to a techie topic that actually comes from a question from client at Gear Monkey.  It involves frame rate and time code.  Specifically, how does frame rate affect time code and what are the differences between the various frame rates like 30p, 29.97, 24 and 23.98?  I will try to keep this one brief and concise so that no one’s brains melt and ooze out of their ears.

First, let’s address time code.  There are essentially two types of time code, drop frame and non-drop frame.  Drop frame time code was created to account for the extra amount of time that it took to broadcast the color portion of the television signal when NTSC was invented.  In order for the time code to match the actual elapsed amount of time, two frames needed to be dropped every minute but not every tenth minute.  During a discussion a few years ago on this subject I asked a group of editors when they thought it was appropriate to use either type of time code.  One editor responded, “Don’t they use drop frame on the east coast and non-drop on the west coast?”  I have never forgot that answer.  The bottom line is that if you are working in standard definition NTSC and will be broadcasting your program (obviously this doesn’t matter for commercials since the program has to be longer than a minute before it matters) then use drop frame time code, otherwise non-drop is fine.  In fact, in any HD format there in no drop frame because you do not need to compensate for the NTSC color delay.

Now, with regard to the varying frame rates available to us in the brave new HD world, here are some tips.  Firstly, let me clarify a few things.  23.98 and 23.976 are the same thing.  The abbreviated 23.98 uses that complex mathematical function known as “rounding.”  Wouldn’t my high school math teacher be proud?  However, 23.98p and 24p are NOT the same thing and I have seen the pain in the eyes of those who have made the wrong choice.  Any footage that will be broadcast or laid off to videotape for final mastering should be done in either 23.98p, 29.97p(or i) or 59.94p(or i).  It is now possible with the advent of things like Final Cut Pro and file based camcorders to create and edit true 24p or 30p projects.  This is fine if your distribution will only be via computer display or if you are printing back to film, however if you want to lay that project off to videotape or broadcast it you will be bummed when you have to re-render that project from 24p to 23.98p or from 30 to 29.97.  I will spare you the long explanation and to why this is, but it has to do with the 60Hz power source we have in the USA and other places.  Some  video cameras refer to 24p or 30p when they are actually referring to 23.98p and 29.97p (i.e. SDX-900, DVX-100, HVX-200, etc.)  If you are shooting with a video camera, you can be fairly certain that you are shooting in either 23.98, 29.97 or 59.94 (i.e. Varicam).  Just make sure that you set up your Final Cut or AVID project accordingly.  For more on this see this older post. 

Feel free to post additional related questions as comments to this post.  In my next post, I will address the issues of color space and color recording formats in current formats.  Happy producing!

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I will be speaking on a panel this Wednesday, March 18th at 6PM covering “VIDEO 2.0 – 2K and 4K HD Production Needs.”  We will be discussing a variety of HD, 2K and 4K techniques, workflows and pitfalls.  The event will be hosted by the MCAI of Orange County at my good friend Brad Hagen’s office.  Come say hello and check it out.  

Here are the details:

MCAI Meeting – March 18th — We’ve got four experts to address the critical needs of high-end HD Production: Do you really need a DITech? How important is on-set color correction? What are the hidden issues of tapeless workflow? Do I need the expense of a video village? And is guerrilla HD possible? Bring all your questions to this important meeting!

Our panel includes experts in all aspects of HD. Their practical experience in shooting (and troubleshooting) and posting native 2K and 4K formats, as well as many other formats, will give you a comprehensive insight into the high end of Hi Def Production.

Click here for more info and to register

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Today’s entry will focus on a very “techie” topic; codecs, compression and frame rate.  At Post Factory we do a large amount of layoffs from client’s hard drives to broadcast tape formats like Digital Betacam, HDCAM and HDCAM-SR.  One of the ongoing discussions that we tend to have with clients is the compression/codec settings of their edited sequences and the frame rate of their project.  With the advent of the Internet and the proliferation of video on the Internet, there has been a lot of confusion about what settings are best.  I would like to address a couple of flawed arguments that I have dealt with over the recent years regarding this topic.

1.  Ideally, try to keep the setting of your sequence the same as that of your original footage.  More specifically, pick the best codec to digitize in and don’t change it throughout the production process.  This can be (and might be someday) the subject of an entire blog entry.  I have talked to more than a few people that edit their entire program in the DVCAM codec, then copy that sequence into a new one that is set for Uncompressed 10-bit and bring it to us – unrendered – to be laid off.  They are convinced that somehow this will improve the quality of their show.  Let me lay this to bed once and for all – it won’t.  But it will take a whole bunch of time to render and likely look worse due to increased compression artifacts.

There aren’t that many of us left that can remember the days of good old composite A/B roll editing where you were very concerned about “generation loss”, the degradation of the signal that occurs when you make successive copies of a shot in order to achieve a dissolve or more complicated effect.  Back then everyone understood that the first generation is always the best.  It didn’t get any better during the process, only worse.  The 21^st century version of generational loss occurs every time you change compression settings and re-render and just like “back in the day” it doesn’t get any better than the original.

2.  There is a big difference between what you can do on a computer and what you can do on broadcast television.  The primary lesson here is don’t bring me a 525/23.98fps sequence and ask to have it laid off.  There is no tape format that will accept those settings.  Before you start editing your project, think about how it will be distributed and plan accordingly.  You can play a 525/23.98fps QuickTime movie on a computer, just not on broadcast TV.  If you are sending your final show or spot to a station or network to be broadcast, then choose from one of the following formats:

      525/29.97fps (Digital Betcam, Betacam SP, DVCAM, DVCPRO etc.)
      720/59.94fps (DVCPROHD or HDCAM-SR)
      1080/29.97fps – aka 59.94i (HDCAM or HDCAM-SR)
      1080/23.98fps (HDCAM or HDCAM-SR)

Stay with one of these setups and you will stay out of trouble.  You can always give us a call at Post Factory before you get started with a project.  We will be glad to talk to you about the best plan for your particular situation and distribution.  Happy editing.

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