4K Raw on a Budget

Convergent Design’s Odyssey 7Q RAW and Sony’s FS700

n March I was very excited to hear that Convergent Design had finally released the highly-anticipated firmware update for the Odyssey7Q SSD recorder that enabled ProRes422 and FS700 4K RAW recording. I’ve been a proud owner of the FS700 for over a year and have loved shooting with the camera. It shares the exact same sensor as the F5, but unfortunately only processes internally, and outputs, 8-bit. The Sony-branded 4K RAW recording solution is very large, but the Odysssey7Q offers similar functionality in a more versatile, compact and affordable package. With the purchase of a license key, the Odyssey7Q is capable of recording a RAW stream from an ARRI ALEXA, Canon C500, or Sony FS700, as well as 4:2:2 1080p to ProRes422(HQ) and 4:4:4 signals to DPX. Some licenses can also be rented on a daily basis. The screen also looks great and with lots of mounting options can serve as a reliable on-camera monitor.

My good friend John Tran helped me conduct my initial technical test. We had both updated our FS700s to v3.0 firmware last summer (required for 4K RAW output) and had been waiting for almost a year to actually record 4K RAW to the Odyssey7Q. Camera assistant Chris Goll kept us organized during the test.

Our test of different recording formats (including the internal AVCHD) focused on these aspects: latitude/dynamic range of available gamma curves and recording formats, bit-depth, chroma-subsampling, and resolution/scaling.

DIY backlit Dynamic Range chart

Photos: Tim Dashwood

The Odyssey7Q’s recording menu currently looks like this:

w 4:2:2 -> PRORES HD (.MOV)

w w w w w w FS700 RAW -> RAW (.DNG)

Canon RAW -> RAW (.RMF)

ARRIRAW -> RAW (.ARI)

4:2:2/4:4:4 -> 4:4:4 (.DPX)

MULTI-STREAM 4:2:2

FS700 4K RAW -> PRORES HD (.MOV)

By Tim Dashwood

The top mode, 4:2:2 -> ProRes HD, is actually ProRes422 (HQ), and is effectively the same 220bps recording function you would have in devices like the Samurai, Ninja, Hyperdeck or Pix240. The “HQ” flavour of ProRes422 is 10-bit, but since the HD-SDI output of the FS700 is only 8-bit (256 shades of grey per R,G,B channel) recording in this mode won’t help with gradients in your image. However, there will still be a decided advantage over recording lower bitrate 8-bit 4:2:0 to AVCHD internally. The FS700′s HD-SDI output is 4:2:2 so the chroma-subsampling is at least better than AVCHD. Recording frame rates of 23.98, 25 and 29.97 fps are available in this mode.

If you want 1080p from the FS700 in true 10-bit, then you will want to purchase the FS700 record key from Convergent Design and use the bottom recording mode FS700 4K RAW -> PRORES HD (.MOV). The 4K RAW setting requires you to change the REC setting in the FS700 to 4K RAW and use either the REC709 or SLOG2 gamma in your picture profile. The FS700 then sends a RAW bitstream to the Odyssey7Q, bypassing the camera’s internal 8-bit processing. The Odyssey7Q debayers the RAW data, crops it from 17×9 to 16×9 and downconverts it to 10-bit, 4:2:2 1920×1080 for recording to ProRes422 (HQ.) The only available frame rates in this mode are 23.98, 25 and 29.97 fps.

The third available option is of course FS700 RAW -> RAW (.DNG), which allows you to record both 2K and 4K RAW streams from the FS700 in 12-bit CinemaDNG image sequences along with a 48KHz 16-bit wav files for sound. Frame rates of 23.98, 25, 29.97, 50 and 59.94 are available for both 2K and 4K resolutions. However, 2K RAW can also be recorded continuously at 100, 120, 200 and 240 fps. 2K RAW at 200 and 240 fps requires RAID0 spanned recording with two SSDs simultaneously, and then the clips need to be re-combined in post-production. Each 4K CinemaDNG frame is about 13.5MB, so each 512GB SSD at 24 fps will only last 26 minutes.

RAW recording requires that the FS700 picture profile have either ITU709, ITU709 (800%) or Slog2 set as the gamma curve. When I started working with the Odyssey7Q I couldn’t figure out why a RAW recorder that takes a RAW data signal would care what gamma processing was set in the camera, except for embedded metadata purposes (a target reference for the debayer process.) I think the intent is to allow the option for the viewfinder and HDMI output to show a ITU709 reference even though many more stops of latitude are being recorded in RAW. The Odyssey7Q currently has an option to set a S-Log2 to REC709 display LUT. Convergent Design tells me this feature will be improved through firmware in the future.

Latitude/Dynamic Range Tests

The first test we conducted was for latitude/dynamic range. Obviously 4K RAW will have the best results when it comes to available latitude, but I was curious how the Odyssey7Q’s debayer/downconvert to ProRes422(HQ) would compare. To conduct the test I cut 17 pieces of ND.3 gel, stacked and stapled them to a piece of foam core with a hole cut for backlighting by a Diva light. This effectively gave me a 17 stop chart. It may not be as photometrically accurate as DSC Labs’ Zyla, but more than enough to compare settings with the FS700′s sensor.

Latitude/Dynamic Range Test: This diagram presents the same chart recorded to 8-bit AVCHD, 8-bit to Pro-Res422(HQ), RAW to 10-bit ProRes422(HQ), 2K RAW, and 4K RAW.

For comparison, I presented in a diagram the same chart recorded to 8-bit AVCHD, 8-bit to ProRes422(HQ), RAW to 10- bit ProRes422(HQ), 2K RAW, and 4K RAW. Slog2 is the preferred gamma curve for the most latitude, but we also shot with REC709 for comparison, and a few of the other popular gamma curves (only available in 8-bit.) For direct comparison the exposure did not change between gamma curves and recording mediums. We set the farthest right white level to the clipping point in S-Log2 when the Odyssey7Q was in RAW record mode. The dynamic range advantage is obviously given to RAW CinemaDNG recordings at just over 12 stops, but the 4K RAW to 1080p ProRes S-Log2 only has around 1-stop less latitude retained than RAW (clips a stop from the top.) Of course, those shadow areas are well into the noise-floor so I would still say the “usable” latitude is 11 stops in RAW or ProRes. Another interesting discovery for those who haven’t upgraded their FS700 yet, is that the Cine4 curve still retains almost the same latitude as SLog2, but has a distinctive S-shape to the curve, which means less need for colour grading in post (adding back contrast), and less chance of having to dig deep into the shadows where 8-bit banding will cause an issue.

The other interesting thing to note about the FS700′s 8-bit processing, versus Odyssey7Q’s 10-bit, is that the 8-bit processing always has a lifted pedestal, whereas the Odyssey7Q uses every available bit. The practical advantage to this is likely to ensure the user is seeing all the detail available when recording, but also keeps the signal out of the lowest bit values where the toe will lend itself to banding. It also looks like the ITU709 (800%) curve would be very useful in low light scenarios, even in 8-bit AVCHD. I would rate it at 4000ISO at 0dB gain – and it still has 10 usable stops of latitude!

Now if you really need to dig deep into the noise floor you can see (with the help of Photoshop’s CinemaDNG Camera Raw decoder and highlight recovery) that there are actually up to 15 defined stops recorded in the Raw file!

Chroma Sub-Sampling

Anyone who has ever tried to shoot and key green screen with a 4:2:0 camera knows all too well the shortcomings of extensive chroma subsampling. The internal AVCHD recording of the FS700 uses 4:2:0 chroma-subsampling, but the external outputs can provide 4:2:2 chroma-subsampling. A debayered RAW recording provides an effective 4:4:4 RGB image.

Chroma Sub-Sampling Test: These samples were normalized in DaVinci Resolve before the screen grabs were taken.

Well there are no surprises here. Less chroma-subsampling results in a cleaner image. What is interesting is the detail level in the RAW originated ProRes 1080p 4:2:2 versus the signal recorded in ProRes from the HD-SDI 4:2:2. Once again, the strength of 4KRAW RGB to 10-bit ProRes422(HQ) over direct HD-SDI 8-bit 4:2:2 recording is evident.

Resolution

Obviously 4K resolution will be better than 1080p, but I was interested how the 2K RAW recorded from the FS700 and wondered if it would be better or worse than 1080p? We used a 35 mm Leica prime at F4, and an “HD” resolution chart.

Unfortunately the obvious debayering/moire issues with 2K RAW are likely the result of the 4K optical low pass filter.

Results of the resolution test.

Sony’s solution to this on the F5/F55 was to create a userswappable 2K OLPF, but we don’t have that option on the FS700. Also, I’m not sure exactly what is going on with the file size, but the resolution of the 2K file is 2048 x 1072, not 1080? Where did those extra 8 lines go, or does it have something to do with pixel binning at 2K? All 2K issues aside, the obvious winners here are 4K RAW and ProRes422(HQ) downscaled from 4K RAW.

Postproduction

All of the ProRes422(HQ) files worked as expected in all the Mac apps I tested (Avid, Premiere Pro, Final Cut Pro 7/X, Quicktime Player 7/X and DaVinci Resolve). However, only DaVinci Resolve truly handled the RAW CinemaDNG files without any extra effort. Avid MC7 currently requires the use of Resolve to “round trip” proxies of the RAW files. The current version of Premiere Pro CC imported the DNG image sequence + wav properly, but presented the linear RGB with a completely purple haze. Final Cut Pro X 10.1 can’t seem to import the image sequence properly and instead requires an impractical work-around by creating separate compound clips with all the separately imported frames. FCP did, however, interpret the gamma correctly and I was able to easily convert the linear RGB to an SLog2 style curve with my Camera Gamma plugin.

The Odyssey7Q base unit sells for $2295 USD and the Sony FS700 perpetual license is $795. More information is available at www.convergent-design.com

CSC associate member Tim Dashwood is the founder of 11 Motion Pictures and its sister companies Dashwood Cinema Solutions and the Toronto-based stereoscopic 3D production company Stereo3D Unlimited Inc.

Edited and reprinted from Dashwood Cinema Solutions. The original version of this article is available at: www.dashwood3d.com/blog/the-odyssey7q-and-sony-fs700/