Editor’s Note: This article from 2017, written by AbelCine’s Andy Shipsides, brilliantly and concisely explained exactly how the then relatively new idea of RAW video worked. The article explained what RAW video was and what the technical and workflow ramifications were for early adopters. Since the article was published, technology has continued its relentless march forward and shooting RAW in 2021 is now much less of a novelty than it was four years ago when the article was originally published. New RAW formats were introduced and cameras and recording devices now offer users many more choices for shooting RAW at much lower price points than previously possible. The article has been updated to reflect the current state of shooting RAW video in 2021.
At the video rental house AbelCine, where I work as the Chief Technology Officer, we offer a class on video formats that covers a variety of different terms and compression formats. One of the more common questions I’m asked is, “What’s the difference between uncompressed video, raw and Log recording?” With so many cameras these days offering different recording options, combined with the popularity of external recorders, it’s no wonder there are a lot of questions about this topic. Recently, I was asked if shooting Log was like shooting raw. A short answer is, “Well, yes and no,” which I know isn’t terribly clear. Raw recording is very different than Log, but they have similar applications. To really answer the question, and to understand the difference between all of these formats, we need a little bit of background. ARRI’s ALEXA camera is unique in that it can output raw, uncompressed and record in a Log format, so I’ll use that camera as an example throughout this discussion. Let’s start with raw, which comes first for many reasons.
I Like My Formats Raw
The idea of raw recording for motion pictures wasn’t popular until the release of the RED ONE camera many years ago. RED brought the idea of raw recording to the masses, though they weren’t the first. Both ARRI and DALSA had cameras that could output raw sensor data. Raw recorders weren’t exactly common on-set gear though, so we have to hand it to RED for getting the raw party started in the motion picture business with their REDCODE .R3D internal compressed RAW. Around the time this article was originally published in 2017, Canon introduced a camera that was capable of recording compressed RAW in camera to CFAST 2.0 cards, the Canon EOS Cinema C200. At the time, while RED had some cameras that were somewhat affordable, the C200 offered internal recording to Canon’s Cinema RAW Light format for a mere $7,500.00, much less money than even the bottom of the line offering from RED, once you factored in building up a RED DSMC system into a usable configuration.
The need to use an external recorder to be able to record RAW images was supplanted by both RED’s camera line up and Canons C200’s ability to record compressed RAW internally to relatively inexpensive cards. The C200 was something of a sign of the floodgates of RAW recording opening up to a wider, more mainstream group of users because of it’s realtively low price. Since then, with the popularity of new mirrorless, DSLR and other new brands of cameras like Kinefinity, ZCAM and others, at times paired with external recorders, recording RAW is now within the reach of the majority of users.
So what is raw video anyway? Simply put, it’s just sensor data before any image processing. In a single-sensor camera, like the ALEXA, color is produced by filtering each photosite (or pixel) to produce either red, green or blue values. The color pattern of the photosites most often used is the Bayer pattern, invented by Dr. Bryce E. Bayer at Kodak. The raw data in a camera like this represents the value of each photosite. Because each pixel contains only one color value, raw isn’t viewable on a monitor in any discernible way. In a video signal that we can see on a monitor, each pixel contains full color and brightness information; video can tell each pixel on a monitor how bright to be and what color. This means that raw isn’t video. Raw has to be converted to video for viewing and use. This is usually done through a de-Bayer process, which determines both color and brightness for each finished pixel in your image. The converting of raw information into video can be time-consuming for postproduction, though great tools are available to make it fairly painless. The upside to raw recording is that no typical video processing has been baked in. The sensor outputs exactly what it sees—no white balance, ISO or other color adjustments are there. This, along with a high bit rate, allows for a huge amount of adjustment in post.
Every camera has a “raw” step in the image-capturing process. The sensor information is always gathered before converting to a video output, but not all cameras let you record or output that data. While raw output was rare when RED and ARRI popularized it, now a whole range of video cameras capture and record in raw, including those from BlackMagic, Canon, Sony and others.
So if the raw data is the real information coming off the sensor, does that mean that it’s uncompressed? This is where things get a bit trickier.
How Uncompressed Is It?
Raw data isn’t necessarily uncompressed. In fact, it’s usually compressed. The RED cameras shoot in REDCODE, which has compression options from 3:1 to 18:1. Likewise, Sony’s F65 has 3:1 and 6:1 compression options in F65RAW mode. The raw data is compressed in much the same ways that traditional video is compressed, and the process does have some effect on image quality. How it shows up in the finished video output can be hard to detect, and the less compressed options in both of these cameras are often considered fairly lossless (limited quality loss). On the other hand, ALEXA outputs uncompressed raw data, which can be recorded externally. This would be the closest thing to a true uncompressed signal.
So what about uncompressed video? The term “uncompressed” obviously implies a lack of compression, but it isn’t exactly clear what this means in terms of video. As we said before, video is derived from raw data off a masked single sensor, or something like a 3-CCD imaging block, and usually something is lost along the way. Raw data is usually at high bit depth, between 12- and 16-bit, but video is usually around 8- or 10-bit. In RGB (4:4:4) video, each pixel contains color and brightness information, which would be rather large with 16-bit depth. So, video is generally reduced in bit depth. Additionally, color information is generally reduced as well, from 4:4:4 to 4:2:2. These are both forms of compression that happen in the camera, even before recording. A standard for HD-SDI output on a professional camera is considered to be uncompressed; however, the specification for a single HD-SDI output in a 1920×1080 resolution is 10-bit 4:2:2. Is HD-SDI not uncompressed then? Well, it’s still uncompressed in the sense that there has been no block, wavelet or temporal-based compression applied. Therefore, we can call it uncompressed 10-bit 4:2:2 video—sounds better than color and bit subsampled video, doesn’t it?
The ALEXA can output uncompressed video over its HD-SDI outputs, either in 10-bit 4:2:2 (over Single-Link HD-SDI) or 10-bit 4:4:4 (over Dual-Link HD-SDI). Oddly enough, the camera can record in 12-bit 4:4:4 ProRes internally, but a standard HD-SDI only supports 10-bit. In this case, the uncompressed output is more limited in bit depth because ARRI is conforming to the standards of the signal.
The state of raw video recording in 2021 has progressed since 2017 by quite a bit. In particular, Atomos has raw recording workflows from inexpensive DSLR and mirrorless cameras using Atomos recorders like the Ninja V+ which provides RAW over HDMI support for the Sony A7 SIII, ZCAM E2 Series, the Nikon Z Series, the Lumix S Series and other video cameras like Sony’s FX9 and FX6. Low cost RAW recording has pretty much become accessible to almost anyone buying a new mirrorless or video camera.
Both Apple and Blackmagic Design have introduced their own flavors or compressed RAW recording, Apple with ProRes RAW and Blackmagic Design with BM RAW. Canon has continued on with Cinema RAW Light in their cameras. The only serious downside of all of this RAW innovation is that all of these flavors of compressed RAW recording are not cross compatible. Each variant offers its own pluses and minuses so it pays to do your research before investing in a raw capable camera and workflow, if raw sounds appealing for your work?
But if raw is raw and video is video, then what the heck is Log recording?
Bump On A LOG
Many cameras, including those from Sony, Canon, Fuji, Panasonic, RED and ARRI cameras have a Log recording mode. When the Log modes are activated, the image becomes flat and desaturated, but you can still see it on a monitor. This should clue you in that Log recording is just standard video recording in the sense that all pixels display color and brightness information. Log isn’t raw; it’s video. However, it’s a special way of capturing that maximizes the tonal range of a sensor.
The idea of Log recording came about with Kodak’s Cineon system for scanning film. The system scanned film into a Log format that corresponded to the density of the original film. This maximized the information from the film that could be stored in the video format. Because this information has many shades of gray—very low contrast—it needs to be corrected for proper viewing on a monitor.
Sony, Canon and ARRI and the others have all taken the idea of Log film scanning and applied it to their sensors. They map a “Log” gamma curve that pulls the most information off of their sensors. Sony calls their map S-Log, Canon’s is Canon Log, and ARRI’s is LogC. Each is designed for a specific camera, but all have a similar result. Because Log is a video image, manipulations like white balance and ISO are baked in. A transform of this video data, known as a lookup table (LUT), is required for proper viewing, which makes the video look more “normal” to us. A standard LUT converts the Log video to standard (Rec. 709) HD video.
Since the popularity of shooting Log and LUTs greatly accelerated over the past few years, there are also many more choices for LUTs with third parties creating and selling their own “LUT packs” to give your Log footage almost any basic look you desire. Tools like FilmConvert have become popular to apply specifically developed LUTs, along with film grain and color correction tools to let the end user use LUTs creatively. None of this changes what Log footage is or what a LUT is, but these new developments have practical ramifications for users who like to experiment with the look of their footage.
The ALEXA converts its raw data into LogC video; this information can be recorded or sent out over HD-SDI. A LUT can be applied for viewing and also can be recorded if desired. Because of this, any step in the chain—raw, LogC video or standard video—can be recorded.
Putting It All Together
So, going back to our original question, “Is shooting Log like shooting raw?” The answer is still “yes and no.” Hopefully, now you can see why. Raw is not Log because Log is in a video format, and raw is not video. Raw data has no video processing baked in and has to be converted into video for viewing. Log is video and has things like white balance baked into it. They’re very much not the same; however, they’re both designed to get the most information out of the sensor. Raw is getting everything the sensor has to offer; likewise, Log curves are designed to get the most tonal range out of the sensor. While they’re very different formats, they have the same general application. Both raw and Log can be uncompressed, but that depends on the recording device. These terms, and many others, have all become part of our vocabulary in this digital cinema world. Hopefully, this article has helped you navigate them just a little bit better.
The Rules of LOG Exposures — How to meter and capture footage when shooting in LOG for the maximum tonal and dynamic range.
Understanding Look Up Tables (LUTs) — An explanation of the settings used to accurately perform color grading on digital video footage.
3D Lookup Tables — A further examination of LUTs and how they work with high-end digital cine camera.
Andy Shipsides is a N.Y.-based Camera Technology Specialist and Chief Technical Officer of the famed rental house AbelCine, where he also ran the training department.
Updated by Dan Brockett in July 2021.