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

[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:

• A frame size of at least 4K
• Expanded brightness levels and deeper shadow capture. (Values are measured in nits, not IRE.)
• Expanded colors that exceed the Rec. 709 color space; mostly in the blues and greens.

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.”

• 8-bit video provides 256 steps of gray or color.
• 10-bit video provides 1,024 steps; four times more.

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.

• If you have the time and camera that supports it, shooting LOG provides the widest flexibility both in terms of image quality and the projects where it can be used. However, no one releases a film in LOG – it’s a tool used in shooting and sometimes grading to produce an end product either in SDR (Rec. 709) or HDR (HLG, HDR10 or Dolby Vision).
• RAW is a special use case. The potential for higher image quality is there, but amazing work can be done without recording RAW.
• HDR is the format of the future, but not all distributors want or need HDR. Many productions don’t have the budget to make HDR look good. And any project that is on a tight deadline is wise to avoid it.
• Also, while HDR is a growing trend, you will still need to produce an SDR version of the same project. While this SDR conversion is somewhat automated, a second color grading pass will be required. So creating an HDR project is a significant commitment of post-production time and resources.
• 10-bit is an ideal editing format, because it gives us room to work magic with effects and color grading. 10-bit defines the size of the room. What we put in it depends upon what we shoot.

ADDITIONAL RESOURCE LINKS

• The Filmmakers Handbook, by Steven Ascher.
• Pocket Lint: What is HDR?

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