Monster Guide: HDR10 in Resolve Studio 18 (Part V)

Part I: Project settings

Part II: BT.2020 or P3-D65 Limited?

Part III: HDR Palette, project render settings, generate MaxCLL and MaxFall HDR10 metadata

Part IV: HDR to SDR Conversion LUT for YouTube

Part V: RAW

Part VI: The Grade

Part VII: The State of HDR Film Emulation LUTs & Plugins

Part VIII: Why HDR Production Monitors Matter

Avoid Y’CbCr
For HDR projects, steer clear of recording XAVC S-I 4:2:2 internal if at all possible. Art Adams explains:

“The Y’CbCr encoding model is popular because it conceals subsampling artifacts vastly better than does RGB encoding. Sadly, while Y’CbCr works well in Rec 709, it doesn’t work very well for HDR. Because the Y’CbCr values are created from RGB values that have been gamma corrected, the luma and chroma values are not perfectly separate: subsampling causes minor shifts in both. This isn’t noticeable in Rec 709’s smaller color gamut, but it matters quite a lot in a large color gamut. Every process for scaling a wide color gamut image to fit into a smaller color gamut utilizes desaturation, and it’s not possible to desaturate Y’CbCr footage to that extent without seeing unwanted hue shifts. My recommendation: always use RGB 4:4:4 codecs or capture raw when shooting for HDR, and avoid Y’CbCr 4:2:2 codecs. If a codec doesn’t specify that it is “4:4:4” then it uses Y’CbCr encoding, and should be avoided.”

This is the consensus of industry professionals, including post production houses, who prefer to see RAW for HDR projects. This is also why streaming platforms like Netflix use the ICtCp color space. For those wanting to future-proof their material or who might need to create a Dolby Vision master in the future:

“Dolby Laboratories recommends using certain types of source material for creating high quality Dolby Vision content. In general, the best source material for Dolby Vision best retains the native color gamut and original dynamic range of the content at the time of its origination.

Original camera footage

For mastering first run movies in Dolby Vision, the original camera raw files or original film scans are ideal.

• Film: Original Camera Negative (OCN)
• Digital: Camera RAW”

Shoot 12-bit or higher
Matthew Bilodeau provides further grounds for preferring 12-bit RAW to 10-bit Log:

“… if you’re considering which codecs to use as intermediates for HDR work, especially if you’re planning on an SDR down-grade from these intermediates, 12 bits per channel as a minimum is important.  I don’t want to get sidetracked into the math behind it, but just a straight cross conversion from PQ HDR into SDR loses about ½ bit of precision in data scaling, and another ¼ – ½ bit precision in redistributing the values to the gamma 2.4 curve, leaving a little more 1 bit of precision available for readjusting the contrast curve (these are not uniform values).  So, to end up with an error-free 10 bit master (say, for UHD broadcast) you need to encode 12 bits of precision into your HDR intermediate.”

“Converting one 10-bit format into another 10-bit format will reduce the performance of the signal and should be avoided whenever possible.” – HDR: A Guide to High Dynamic Range Operation for Live Broadcast Applications, Grass Valley

Linear raw excels at capturing highlight information and what you will find is that compared to log there will be more textures in highlights and brighter parts of your captured scenes. This will become more and more important as HDR screens are better able to show highlights correctly. Current standard dynamic range displays don’t show highlights well, so often the extra highlight data in raw is of little benefit over log. But that’s going to change in the next few years so linear recording with it’s extra highlight information will become more and more important.

Generation Media

RAW is future-proof
Yet another seldom discussed advantage of RAW is that, when shooting log, the quality of the file is completely at the mercy of the camera’s internal encoder, meaning that it’s not possible to improve upon this or change the gamma/color space at some point in the future; whereas with RAW, the image quality is determined by the debayering process in post, giving you the ability to re-encode the footage with a higher quality encoder when one becomes available. 

In our own experience, and from watching countless videos uploaded by others, RAW will give significantly better results and there’s no way we’d go back to shooting Log for HDR. Not to mention that the a7s III 4.2K ProRes RAW files contain nearly 25% more resolution, with no baked-in denoising, lens corrections, in-camera sharpening or other enhancements applied.

Click on image below to enlarge.

Noise

HDR tends to amplify existing noise in the image, particularly in shadow areas. De-noising in post with either Resolve’s own built-in denoising software or Neat Video will give better results.

And here’s the same ProRes 4444 clip with a small amount of spatial noise reduction in addition to the temporal. Mode faster – radius small – Luma 2 – Chroma 2.

There’s also more color information to work with in the RAW clip than in the XAVC S-I internal clip:

From best to worst

“If you’re using a prosumer or entry level professional camera, taking a few preparatory steps to set up how you’ll actually be capturing the image can mean the difference between getting footage that can be used in HDR mastering, vs. footage that can’t.

1. 16 bpc > 14 bpc > 12 bpc > 10 bpc > 8 bpc: 10 bpc should be your minimum spec.
2. RAW > LOG > Linear > Gamma 2.4: avoid baking in your gamma at all costs!
3. Camera Native / BT.2020 > DCI-P3 > Rec. 709 color primaries
4. RAW > Compressed RAW > Intraframe compression (ProRes, DNxHR, AVC/HEVC Intra) > Interframe compressed (AVC/H.264, HEVC).” – Samuel Bilodeau, Mystery Box

Flexibility in post
Mark Spencer demonstrates how, with the same extreme grade applied, the Sony internal XAVC file falls apart much more easily than the ProRes RAW one:

Lift, gamma, gain
It should be mentioned here that traditional lift/gamma/gain wheels are unsuitable for grading HDR, just one reason why DaVinci Resolve, with its HDR Color Palette, is preferable to Final Cut Pro.

“It is also worth bearing in mind that the traditional lift, gamma, and gain operators are particularly unsuitable for acting on ST 2084 image data, where 0-1 represent zero to 10 000 cd/m². Highlights, in particular, can swing uncontrollably into extreme values as a result of small changes. Modern grading systems offer alternate grading operators tailored to the needs of HDR grading.” – Nick Shaw

S-Gamut3 or S-Gamut3.cine?

For Color Gamut for RAW Output, select either S-Gamut3/S-Log3 or S-Gamut3.cine/S-Log3. For what it’s worth, S-Gamut3.cine/S-Log3 is the most common color space used on Sony FX9, F55, FS7, F5 and FX6 Netflix productions (which also happen to use the P3-D65 color space in post-production). We’ve also been informed that key mastering engineers at Sony Pictures in Culver City recommend selecting the S-Gamut3.cine/S-Log 3 settings in Resolve. S-Log3 is recorded as Full range. There is no option to select Legal range. RAW is sensor native data and does not apply any color space or log curve – only the color space metadata is saved. RAW is recorded as 16-bit linear which is then compressed and recorded in the Ninja V as 12-bit ProRes RAW. The color space is applied to the RAW data during the de-Bayer process.

Exposure is critical. Avoid blown-out highlights and overexposed skin at all costs.

In order to work with ProRes RAW footage in DaVinci Resolve, first you’ll want to convert it to cDNG. Download RAW Convertor from the Apple App store.

Project settings:

After dropping the folders onto the timeline of the Edit page, you’ll be able to make adjustments to the clips in the Camera RAW tab on the color page of DaVinci Resolve. If you’re grading with an OLED TV, we recommend reducing exposure beforehand to avoid frying your display!

Here’s a comparison between lossless, 3:1 and 5:1 cDNG:

Alternatively, you can transcode ProRes RAW to ProRes 4444 XQ. Import your ProRes RAW files into Apple Compressor and select ProRes 4444 XQ.

Compressor will automatically choose S-Log3/S-Gamut3. If you would prefer to work with S-Log3/S-Gamut3.cine, in the video tab, select S-Log3/S-Gamut3.cine for the RAW to Log conversion. Compressor will then automatically choose S-Log3/S-Gamut3.cine for the Camera LUT.

After importing your ProRes 4444 XQ files into DaVinci Resolve, you’ll need to change the Input Color Space to Same as Timeline.

RED Komodo Workflow

RED: Exposure Strategy

The histogram

Our goal should be to avoid clipping in the highlights while maintaining acceptable noise levels. The principal tool for judging exposure levels is the histogram, which shows the precise luminance levels of the red, green, and blue pixels after setting the ISO and white balance. Monitors, while indispensible, are less than ideal for gauging brightness.

The histogram allows us to see how brightness is distributed throughout the image and how near the shadows and highlights are to clipping. However, the histogram alone is incapable of indicating correct exposure: it can’t warn us of areas in the image that are about to, or that have already clipped, which is where the false color tools and traffic lights come in.

False Color Modes

The RED Komodo has two false color modes: false color exposure and false color video. The false color exposure mode alerts us to clipping in the highlights (indicated in red) and clipping in the shadows (purple) in addition to indicating 18% gray (green). There is often a great deal of exposure latitude here before an excessive amount of purple or red occurs.

False color video mode furnishes us with more granular information regarding brightness levels in different areas of the image but should be used at ISO 800 and above for the most accurate results. Its colors are based on IRE values, not the RAW data and is useful for evaluating lighting and for adjusting a suggested look prior to sending footage off to post-production. There are nine levels, with green representing 18% gray, pink corresponding with typical Caucasian skintones, teal signifying textured shadows and straw, yellow and orange becoming ever closer to white, while the remaining colors indicate the tonal extremities.

Traffic Lights

The red, green and blue dots, commonly referred to as the traffic lights, inform us of when a particular color channel is clipping. When around 2% of the pixels for an individual color channel have become clipped, the corresponding traffic light will be triggered. Sitting between the highlight and shadow traffic lights are the goal posts. The fullest extent of each goal post represents a quarter of all the image pixels for a particular color channel. Ordinarily, the shadow goal posts can be raised by as much as 50% and still yield acceptable noise levels: but even a miniscule amount in the highlight goal posts can spell disaster, especially in HDR.

RED Exposure Strategy in Practice

Our recommendation is to use the histogram and traffic lights and expose to the right by opening up the iris until the lights turn on, then gradually reducing exposure until they disappear. The advantages are being able to quickly arrive at the optimal exposure with no guesswork, shallower depth of field and less noise in the image. The following is a comparison between using false color video mode to nail exposure of the subject vs. ETTR.

Below, you can see what the viewer looks like in the RED Control app. The screenshot to the left was exposed using false color video mode with skin tones placed between 61-70 IRE, while the one to the right was exposed to the right using the histogram and traffic lights.

One downside of ETTR is that it we’re no longer dealing with WYSIWYG: it can be difficult if not impossible to see the image when exposing to the right.¹

1. In ‘Cinematography: Theory & Practice’ Blain Brown writes, “RAW, in this context, is an absolute scale based on the output of the sensor. It is not necessarily related to the viewing image in terms of brightness values. […] This is, of course, the basic concept of shooting RAW vs. shooting video that is more or less “ready to go.” Shooting RAW/Log is not about producing a final image, it’s about producing a “digital negative” that has great potential further down the line. The downside is that the images are not directly viewable and this makes using exposure tools like zebras and histograms pretty much useless — they can only be used as approximation.” Brown then goes on to outline several different exposure strategies and concludes that, “In practice, cinematographers rarely use ETTR on feature films or other long-form projects.” From the reading we’ve done, the issue DPs have is not that ETTR doesn’t exploit the sensor’s capabilities but that, when grading hours-long movies and episodic television shows, it requires more work in post to realize those benefits. Then there are cinematographers like Erik Messerschmidt, who alternate between approaches according to the circumstances.

Below are the same two clips: false color video mode (L) and ETTR (R), showing false color exposure mode. Green represents middle gray, the absence of red indicates no clipped highlights.

Above, waveform monitor false color video mode (L), waveform ETTR (R)

The difference in noise between the two exposures is dramatic. Granted, this is a worst case scenario! Click on the screenshots below to enlarge (you may have to increase the brightness of your display and watch in a darkened room to see the images).

You’re encouraged to examine the two clips back-to-back by downloading the video here (HDR). No color correction or noise reduction in post.

In addition to adjusting the aperture to control the amount of light striking the sensor, RED has another trick up its sleeve: ISO can be used to precisely determine the number of stops of dynamic range/latitude above and below middle gray. If you’re shooting outdoors in bright light, ISO 800 will probably give you the best balance between highlight and shadow latitude; if you’re indoors or working in low contrast lighting, a lower ISO, which allocates more dynamic range to the shadows, reducing the appearance of noise, is preferable. At the same time, if you’re working on a film, you don’t want to have wild swings in ISO, as that could introduce jarring changes in texture. You can download a video with a back-to-back comparison between ISO 250 and ISO 800 here (HDR).

Another thing to keep in mind is that, while REDCODE RAW has tremendous latitude, at lower ISOs, you’ve got less highlight protection, and correct exposure becomes more critical. Nevertheless, the ability to redistribute latitude/dynamic range above and below middle gray offers creative control that we would never want to relinquish, and it baffles us that many stubbornly keep their ISO permanently fixed at 800. It goes without saying that this is just how we work; if you prefer to use a light meter, waveform monitor, zebras or just eyeball exposure using a calibrated monitor, those are all valid ways of working, too. Lastly, don’t let anyone tell you they’ve done all the tests themselves so you don’t have to: everyone should be performing their own tests to determine what works best for them.

RED Komodo Project Settings