Review: AJA's FS-HDR looks to be a Godsend when it comes to HDR/SDR cross conversion. We take a closer look to see what it can do.
There's often something of a gap between the introduction of a new technique and the ready availability of the tools required to work with it. Other than stereo 3D, HDR is one of the best examples of this: it can require an entirely new transformation, monitoring and display chain. Within that requirement, we're also going to need converters between formats, controls to adjust the video, and ways to solve compatibility problems. These tools are the things which tend to trickle out of the factory gates only once we've identified the problems that need to be solved, and, sure enough, one such device is helping power the uptake of HDR across a range of productions from live television to narrative cinematic projects.
AJA’s most recent release isn’t one of the low-level converter boxes that we might gaffer tape to the back of a monitor; instead it’s based upon a collaboration and “fusion” between the company’s FS series of frame syncs and conversion products, and Colorfront’s highly respected Colorfront Engine; arguably an important component needed to make HDR production really practical. The FS-HDR, available now for a recommended US$7995, comes in a single rack unit and provides a variety of conversion services intended to bridge existing camera equipment to HDR delivery formats as well as real time transforms between SDR and HDR materials and the predominant HDR approaches – HLG and PQ. Colorfront is perhaps best known for its on-set grading and dailies preparation software, and their contribution to AJA's converter makes perfect sense.
As we'd expect, the FS-HDR supports a comprehensive selection of input formats, including log encodings as produced by a variety of prominent camera systems as well as high and standard dynamic range distribution formats, so it can be used as an up or down converter. Camera log formats from Sony, Red, ARRI, Panasonic and Canon are supported for input as well as output; especially helpful if providing a SONY log output for use in their pipelines for instance.
Additionally, recent ACEScct support in Film Mode ensures compatibility for key narrative workflows. Inputs using a combination of various gamma encodings and colour gamuts are also supported, including PQ-encoded 1000-nit pictures in either BT.2020 or P3 D65 gamuts (output can be configured up to 4000 nits when required), HLG in BT.2100 gamut, or, of course, conventional Rec. 709. There is no mention of Dolby Vision, which would be fairly normal as Dolby likes to control its technologies quite closely, although of course for live production, PQ sits at the base of these workflows as well.
Of the supported input formats, it's interesting to note the now well-established application of Sony's SLog3 with SGamut3 colour as an interchange format potentially suitable for live production. Despite being seen and used primarily as a way to store the entire dynamic range of a camera in a file, or possibly to transport it to a monitor for processing and display, it's naturally quite feasible to treat it as an HDR precursor for live production. It's just a way to get the camera's whole dynamic range down a given pipe. The FS-HDR also enjoys compatibility with high-speed 6G and 12G-SDI with HD-BNC optional connectivity, or even fibre for long runs, in order to best avoid the multi-link approach which has occasionally been applied to 4K images, especially at higher frame rates or with increased colour depth. The need to use less capable gear will, naturally, occasionally require a fallback to the standard 3G-SDI multiple links which is included.
There's also a philosophical angle to all this. If we've made a box which is capable of taking a high dynamic range signal and outputting something that's ready for TV display, we're essentially doing the job a colourist does when grading (say) Arri Log C material with the goal of creating a Rec. 709 deliverable. This, of course, is a creative process, at least in terms of a feature film or piece of high-end, often single-camera television. The FS-HDR’s use of the Colorfront Engine is specifically designed to protect as much of the creative intent as possible. Naturally, it isn't really the intent of the FS-HDR to automate that sort of work, any more than that's the purpose of the Rec. 709 lookup tables and knee processing that exist as options inside most broadcast cameras.
However, FS-HDR provides sufficient controls and parameters for tweaking the transform process. and in recent releases has also added user upload support for up to 10 3D-Luts, introduced Dynamic LUT support for Pomfort’s LiveGrade Pro and Wonderlook and continues to offer updates to address user needs as the team continuously learns from the experiences only real world production can provide. Perhaps the product’s greatest strengths are in its single master workflow support of simultaneous HDR and SDR delivery as well as the robust round tripping supported for HDR to SDR and SDR back to HDR which replay systems, commercials and more demand for live production.
The FS-HDR is a fascinating product. It will be interesting to see how systems like this are able to handle the varying demands of conversions to and between HDR and SDR formats, depending on the capability of the camera at the front of the chain, and the target display.
We showed this review to the manufacturer, AJA, which added the following information about the FS-HDR:
"FS-HDR provides myriad controls and parameters for tweaking the transform process. and in recent releases has also added user upload support for up to 10 3D-Luts, introduced Dynamic LUT support for Pomfort’s LiveGrade Pro and Wonderlook and continues to offer updates to address user needs as the team continuously learns from the experiences only real world production can provide. Perhaps the product’s greatest strengths are in its single master workflow support of simultaneous HDR and SDR delivery as well as the robust round tripping supported for HDR to SDR and SDR back to HDR which replay systems, commercials and more demand for live production."
The price of the FS-HDR is $7,995.00