USER REVI EW | BLACKMAG I C RAW
It’s fairly straightforward, of course, to come up with a format that contains all the clip’s frames in a single file. Similarly, their file format can embed metadata that tells the decoding software about the characteristics of the camera sensor, but the engineers at Blackmagic realised that they had an opportunity to introduce some additional benefits. Traditionally, decoding Raw files is slow – mostly because of the complexity of the filters required to de-bayer the sensor data. The sensor has a matrix of red, green and blue pixels – usually with twice as many green pixels as red and blue (because our eyes are more sensitive to the green part of the spectrum). That means you have to ‘invent’ blue and red pixels to combine with each green pixel to produce the final output. Depending on your final output resolution, you may have to invent new green pixels too. To do this well you need adaptive 2D interpolation filters that try to work out where the edges are in the image (so that you don’t use pixels on the far side of the edge to invent new colours on this side, which leads to blurring) as well as looking for correlation between
RIGHT Blackmagic’s new 4K Portable camera may also be able to use the new Raw format.
the colour channels. In fact, there are a myriad of techniques used to make the final image look as good as possible – and they all tax the capabilities of even the fastest computers. NEW APPROACH Blackmagic’s approach is to have the new Raw file format contain partially decoded information. Blackmagic has split this difficult process of de-bayering between the camera – where they can do some processing in dedicated hardware – and software running on the post- production computer.
There aren’t any technical details available at the moment, so it’s hard to know how clever this is, but it sounds very clever indeed. As well as simplifying the decoding task, Blackmagic’s software decoder also uses the special instructions available in modern CPUs, and GPU acceleration with Apple Metal, CUDA and OpenCL to accelerate playback. The upshot is that Blackmagic RAW will play back quite happily on a MacBook Pro with no hardware decoder boards or external GPUs. I even tried it on a fairly aged (2015) MacBook Pro with no issues at all. To encourage other software manufacturers to support their Raw files, Blackmagic has released a software developer kit for Mac, Windows and Linux. RAW OPTIONS Blackmagic RAW is a compressed format with two options. The first produces a constant bit rate (CBR) and offers compression of 3:1, 5:1, 8:1 and 12:1. The second option is a variable bit rate Codec with two settings – Q0 seems to reduce data to between about 20% and 50% of uncompressed, the Q5 setting gives a reduction to around 8% to 20%. Compression sounds like a bad idea, but it’s generally better done on the sensor data than on 4:2:2 image data (which has already been
BELOW Blackmagic’s Resolve BRAW Record and Timeline windows.
64 DEF I N I T ION | NOVEMBER 20 1 8
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