The SMPTE HFR Study Group has been requesting certain Integrated Media Block (IMB) specifications since its outset. Several manufacturers chose to wait until after CinemaCon, and those specs are now in. Nearly all products claim to be capable of a maximum compression bit rate of 500 Mb/s, twice that of the DCI spec and ISO standards. One would think that twice DCI is sufficient for twice the frame rate per eye, as is planned with the 48 fps per eye release later this year of Hobbit. Park Road Post, the post house for Peter Jackson’s movie, says it’s good enough. That, plus the easy generation of a 24 fps version from the 48 fps, is why Hobbit is 48 fps per eye and not 60 fps per eye, as proposed by Jim Cameron for Avatar 2.
But there are notable differences in the specs that remain to be explained. A ground-up JPEG2000 decoder design using an FPGA framework should not have bandwidth issues for the color components. ISO/IEC 15444-1 agrees with this, by specifying a maximum instantaneous bit rate of 200Mb/s for any color component for 24 and 48 fps content, 2K or 4K. (Versus 250 Mb/s for all color components combined.) Intopix appears to have done its homework, as has USL, to remove any bandwidth limitations from their products, and consequently, from products that use their FPGA frameworks. IMBs using these frameworks claim 500 Mb/s throughput for all color components. There is one IMB, however, that does not fall into that category, as currently presented by the manufacturer. Notably, the specs of this particular IMB indicate that there is a bandwidth limitation in some color components, lower than that specified by ISO for 24 fps. This appears to be acceptable for the short term, as no complaints have been heard. Notably, the manufacturer says relief is on the way, so no need to press the panic button…yet.
If a surprise is due, it’ll be when a standard is set for compression bit rate at higher frame rates. When it comes to setting a new standard, simply scaling numbers in ISO is not an approach that cinematographers will readily agree to. To better understand the impact of HFR bandwidth limitations, production planning has begun for the production of a unique set of live shots, the subject of which is designed to artistically stress compression of the image. It’s still useful to have a laboratory-like non-artistic test, so JPEG2000 stress patterns are also being sought for the purpose of stressing image compression at different bit rates. Even with the volunteered services of cinematographers, producers, and world-class HFR production stages such as Cameron-Pace and 3ality, some costs will still be incurred due to union labor and insurance. In short, the production is now in the fund raising stage. But there is no website that says “click to donate.” If your company is willing to write a check, please contact Michael Karagosian for more information. Rights to the raw footage and the final production will be managed by the ASC and possibly the Academy of Motion Picture Arts and Sciences.
