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The Difference Between Raw Video and Uncompressed Video

image sensor

If you follow Videomaker closely, you've likely seen us use the terms raw video and uncompressed video. We might say “Camera A captures uncompressed video” or “Camera B shoots raw.” Hopefully we've never said “Camera C shoots uncompressed raw video.” While they sound similar, they do mean different things and shouldn't be used interchangeably.

So what's the difference? Raw video is uncompressed, right? Well, it is, and raw video is always uncompressed. However, uncompressed video isn't always raw.

To understand the difference between raw video and uncompressed video, we need to understand how a digital camera captures images.

The first thing that happens is light hits an image sensor which turns that information into data. At this point, there is no video. There is simply data—just a bunch of zeros and ones. That data needs to be processed and interpreted as video before it can be seen. This is done by the image processor: a second chip in the camera. The image processor applies things like white balance or gain (ISO). Once the processor interprets the sensor data it compresses it into a video file.

So here we have two data streams in the camera. That's where raw files and video files are created. That end file is the video that you and I normally work with. Some cameras, like the Nikon D800, can send that video out through an HDMI or other connection (SDI), to be recorded before it has a chance to be compressed. It still interprets the image, sends the video through chromatic subsampling (4:4:4, 4:2:2, etc), but there is no additional compression occurring. This footage is much nicer than normal, compressed video, but it's nowhere near as flexible as raw.

Raw footage is simply the plain data from the image sensor before it has a chance to be processed. If you've ever worked with raw data from a video or still camera, you know that there's no image until the data is run through a piece of software that can interpret it (Camera Raw or RedCine-X). When you do this, you get 4:4:4 subsampling and no set color temperature (you can fix white balance in post). It also means that you need to interpret all your footage before you can edit it. Don't expect to be able to drop the files from your new Blackmagic Cinema Camera into your editing software and be able to work with it without interpreting the footage.

Is it worth the hassle? That depends on how much time you have in post and how much of a stickler you are for image quality. If you want to work with raw video, expect to work a lot harder for a much nicer end product. Uncompressed video is going to give you a pretty nice image for the added cost of recording on a device outside your camera. For the rest of us, normal, compressed footage captured to your cameras SD or CF card will probably work just fine.

 

[Image courtesy of BigStock.com]

 

Tags: video, filmmaking, cinematography

 

October 03rd, 2012

Comments

rainbowsofwhite's picture

 

Thanks for the info, very informative.

 

Question : What device records uncompressed video outside of the camera?

 

Just reading the specs on the Nikon D600, it's fine and dandy to say "Uncompressed video via HDMI output" BUT, where does the HDMI go? What is it connected to?

 

 

Camera raw motion footage can be, and is compressed in some cases...RED's raw data is compressed using a derivative of JPEG2K, and CineForm raw uses a proprietary codec...

 

RED r3d files can be dropped on the timeline and edited in Adobe Premiere Pro or Sony Vegas...or handled at reduced resolution in Avid through AMA without "interpretation", sometimes also called "flattening' to a standard raster format of some type.

 

The term "compression" is used to describe so many things...chroma subsampling, transforms...actual data compression.  Interlacing is a form of compression in the basic sense.

 

It seems like this is written more from the perspective of a still photographer instead of a videographer.

Kevin Duffey's picture

You asked where can the uncompressed HDMI go from a camera like the D600/800 and soon the MK3... you can use a very affordable recorder like the Black Magic Shuttle 2, that can record uncompressed, or optionally DNxHD or ProRes on SSD drives. You can also connect it to a computer with an HDMI input using a card like the Black Magic Intensity. I have both the Shuttle 2 and the Intensity and they work really good. 

 

You can also consider buying the Black Magic camera, which has a built in 12-bit RAW recorder to SSD drives, so you get insane RAW recording, or you can also choose DNxHD or ProRes on the camera to record in.

 

The biggest problem is RAW is huge amounts of data. I am not sure the exact amount, but I think a 128GB SSD drive can record about 20 to 30 minutes of RAW. 

 

Lot of people think that's insane. But think of this.. from what I've been reading and discussing, most movies record dozens of hours worth of "takes" but over days and days, if not months of recording. Sure, big budget films/videos can afford to have a dozen 512GB SSD drives on the set. However, for myself, I want to shoot some short few second to 30 second clips at a time, perhpas for b-roll or stock footage. A couple of 256GB SSD drives would afford me a good hour or so of RAW recording. Unless you're recording a kids soccer game or play production, using RAW with short clips is very reasonable for me, given what you get doing so. Anything longer and I'd look at DNxHD or ProRes.

Kevin Duffey's picture

From what I've read.. initially it does not, but they are adding uncompressed output via HDMI to the MK3.. so I would suspect they'll have it for the 6D at some point.

 

Basically it would be called Uncompressed HDMI out or something like that. 

Treen Media's picture

Cool, thanks.

Is "they" Canon? Is this a firmware update?

Without this update is the HDMI output identical to what ends up on the SD card?