Explaining HDR, RAW, Log, LUT & 10-bit Media [u]

Posted on by Larry

[Updated March 21, 2022, adding information about the Apple Studio Display.]

Like many, I get confused about the differences between HDR, SDR, RAW, Log, LUT, and 10-bit media. All too often, the explanations get deeply technical. So, I decided to write an overview, partly for you and partly for me, to help us understand this technology better.

NOTE: I’m indebted to Steven Ascher, author of The Filmmakers Handbook for his help with this article.

I encourage comments and questions.

HDR

In the beginning was SDR (Standard Dynamic Range) media. Then, along came HDR (High Dynamic Range). HDR, like SDR, is a video format. HDR is generally defined as media with:

NOTE: However, it’s possible to have a 1080p HDR video, just as it’s possible to have a 4K SDR video.

HDR includes formats like HLG, PQ, HDR 10 and Dolby Vision. Each of which has specific technical requirements. Not all distributors want or need HDR media. You can create HDR projects from both RAW and Log files, but not media shot using the Rec. 709 (SDR) color space.

HDR media generally requires a color grade to make it look good; though HLG can be viewed directly. It also requires an HDR video monitor to properly view the images. We can’t view or grade HDR using computer monitors.

UPDATE: While the Apple Pro Display XDR supports HDR, the Apple Studio Display does not. M1 MacBook Pros and Mac Studio computers can display tone-mapped HDR inside Final Cut. However, the Mac user interface is still SDR, as are other apps.

The benefits of HDR are improved image quality, greater realism (which is a two-edged sword) and future-proofing media. The disadvantages are larger file sizes, time spent color grading and the extra time and budget required for lighting, lenses and production value to make the improved image quality worthwhile.

NOTE: RAW, Log  and HDR HLG are ways of recording HDR media with a camera. For example, the iPhone 13 Pro shoots HLG media directly.

RAW MEDIA

RAW is data directly recorded from the camera sensor. It isn’t video, it’s data. It’s analogous to an old-fashioned telegraph. RAW media records the beeps. But, in order for us to understand the message, we need to convert those beeps into letters of the alphabet. RAW files must be recorded by the camera, you can’t convert media to RAW after it’s shot.

After recording, all RAW files need processing, called “de-Bayering,” to convert the RAW data into video. Then, it needs a color grade to look good. RAW media is most often converted into HDR, but it can be used in an SDR project.

There’s nothing that ties RAW to HDR or, even in most cases, to a specific frame size or rate. Those are assigned during the de-Bayering process.

STEVE writes: “I personally think RAW is oversold as ‘the best’ given that the vast majority of productions are not done in RAW and they obviously are capable of very high quality.”

The benefit of RAW is that it provides the potential for extremely high image quality, with great flexibility in how it is processed into images. The disadvantage is that the file sizes are large, the files require processing before we can view them, the finished edit requires a color grade, and you need to spend time and budget on lighting, lenses and production value to make the improved image quality worthwhile. RAW recording should not be used for quick turnaround projects.

NOTE: RAW is not an acronym. It means “raw,” as in “unprocessed.” For some reason, we got in the habit of capitalizing it. Too late to change now.

LOG

Log (short for “logarithmic”) records media in a way that captures a wider range of grayscale values (tones) than Rec. 709. Log, like RAW, can be used in both SDR and HDR projects. It records grayscale values in a way that we can extract more detail from shadows and highlights during the color grade. All high-end, and many mid-range, cameras can shoot Log format. However, you need to shoot Log, you can’t convert a file to Log format after it’s been shot.

Also, if you shoot Log, you need to shoot at least 10-bit, which generates larger file sizes.

STEVE writes: “Because Log can capture 12 stops or more of grayscale values it’s a good starting point if you’re working in HDR. It is also a good starting point if you’re working in SDR (which many people do routinely). Yes, it requires color grading but in many situations people throw a Log to Rec. 709 LUT on the material, at which point it they treat it like Rec. 709 (which also usually requires some grading).”

Unlike HDR, Log recordings can be used in any project and can especially benefit SDR because more of the image (shadows and highlights) can be adjusted due to the wider range control over exposure.

The benefits to Log-format media are improved image quality and support for any project. The file sizes are about the same as non-Log files. The only disadvantage is the time required for a color grade.

NOTE: Just to make your head spin, RAW files are often recorded with a LOG curve applied to it. HLG is a format that uses the hybrid log gamma tone curve, where it gets its HLG name. HDR10 and Dolby Vision are formats that frequently use the PQ tone curve.

LUT

A LUT (Look-Up Table) is a conversion table that tells the computer how to convert the numeric value of each pixel stored on disk into pixels displayed on the screen. ALL video uses LUTs. Think of a LUT as a translator. The pixel data is stored on the hard disk in Spanish. The LUT translates it into French, or English, or…any other language you want. The translation is instant and requires no rendering. You can change LUTs at any time during the editing process.

LUTs are often used for LOG, but are also often used to emulate a film stock or a particular look for people who shoot any kind of material (RAW, LOG, Rec. 709, Flat Profile, etc.)

STEVE writes: The newer trend in color grading is color managed workflows (Resolve has this nailed) where you let the app automatically convert footage from any camera/format to the color space of the timeline (using a transform), then select the output you want (TV, web, theatrical) using another transform. No LUTs involved.

10-BIT

Bit depth describes the number of steps between the absence of something – black – and the maximum of something – white. Or “no red” to “all red”. Or blue. Or green. Bit depth manipulates the gradients and shades of a color. Higher bit depth makes gradients smoother, color changes subtler and sunsets more “real.”

All ProRes files are 10-bit, even ProRes Proxy. Most AVC files are 8-bit. Most H.264 files are 8-bit. Most HEVC files are 10-bit. Many cameras only shoot 8-bit images. (Higher-end cameras can shoot 10-, 12-, even 14-bit media.)

If you shoot an 8-bit format, when you convert it to 10-bit for editing, you still have only 8-bit source images. However, there’s a big advantage to converting 8-bit media into 10-bit. As an analogy, if I dump five gallons of water into a bathtub, the bathtub may be bigger, but I still have only five gallons of water. The cool part about the extra space in the bathtub, though, is that if I add more water, perfume or soap and stir quickly, nothing spills out. I have plenty of room for whatever I want to add.

Just so with video. Moving 8-bit video to a 10-bit codec provides plenty of room for effects and color grading. The images may still only be 8-bit, but effects and color grading are calculated in 10-bit. The “color space” is bigger and nothing spills out.

NOTE: This is one of the reasons converting camera files to 10-bit media, such as ProRes, improves the quality of color grades and effects.

SUMMARY

All of us want to create great images. We also want small files, large frame sizes, efficient editing and images that look perfect out of the camera. That kind of magic doesn’t – yet – exist.

ADDITIONAL RESOURCE LINKS


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10 Responses to Explaining HDR, RAW, Log, LUT & 10-bit Media [u]

  1. Lou Hemsey says:

    Excellent, Larry and Steve. Concise and clearly delineated.
    Lou
    Lou Hemsey Music and Film

  2. Steve Berown says:

    Thanks Larry. The tech world is constantly evolving. That’s for being a guide that walks us through the differences.

  3. That is so good to know. Really fills in the gaps of what I THOUGHT I knew. Thank you so much for the clarification.

  4. Leigh Reeves says:

    Thanks Larry. I’v had trouble getting my head around the different formats. I think I have a 9 bit brain. There’s only room for a bit more!

  5. Thanks, Larry. This is very helpful. I’m circulating this to many of my contacts.

    You wrote: ” We can’t view or grade HDR using computer monitors.”

    Does this mean that even wide gamut, high-end monitors from Eizo, can’t be used? Or Apple’s new 6K monitor?

    – Bryce

    • Larry says:

      Bryce:

      My understanding, prior to reading the links you sent, is that HDR requires a video monitor, not a computer monitor. However, I’m happy to do more research.

      Larry

    • Larry says:

      Bryce:

      Thanks for the links – I’m looking forward to reading them.

      Larry

    • Larry says:

      Bryce:

      After reading these, the DaVinci Resolve workflow acknowledges that using computer monitors for viewing HDR does not represent the full grayscale range of HDR. It is a work-around.

      Apple is talking about viewing HDR10 (a distribution format) on computers and Apple TV. The only monitor they suggest using for monitoring “native” HDR during the editing process is the Pro Display XDR.

      The three Eizo articles define HDR (Articles 1 & 2) and then pitch using EIZO external video monitors for monitoring HDR (Article 3). Clearly, there are a variety of HDR Video monitors from Eizo, Flanders Scientific, Sony and others that we can connect to our computers for accurate HDR monitoring. But these are not computer screens.

      None of these articles suggest that current computer monitors are sufficient for monitoring HDR media during the editing process. They say computer monitors can come close, but are not there yet.

      Larry

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