do you need raw video?

We are finally there. Thanks to smaller companies that are keen to get a share of the market we now have at least two cameras with MFT sensor that are able to produce RAW video.

RAW Video and RED

It has been RED to patent the original algorithm to compress raw video data straight out of the sensor before the demosaicing process. Apple tried to circumvent the patent with their ProRes RAW but lost in court the legal battle and now has to pay licenses to Red. Coverage is here.

So RED is the only company that has this science, to avoid paying royalties Blackmagic Design developed an algorithm that uses data taken from a step of the video pipeline after demosaic for their BRAW.

I do not want to discuss if BRAW is better than RedCode or ProRes RAW however with a background in photography I only consider RAW what is straight out of the sensor Analag Digital Converter so for me RAW is RedCode or ProRes RAW and not BMRAW.

How big is RAW Video

If you are a photographer you know that a RAW image data file is roughly the same size in megabytes than the megapixels of your camera.

How is that possible I have a 20 Megapixel camera and the RAW file is only a bit more than 20 megabytes? My Panasonic RW2 files are 24.2 MB without fail out of 20.89 Megapixels so on average 9.26 bits per pixel. Why don’t we have the full 12 bits per pixel and therefore a 31 MB file? Well cameras are made of a grid of pixels that are monochromatic so each pixel is either red, green or blue. In each 2×2 matrix there are 2 green pixels, 1 red and 1 blue pixel. Through a series of steps of which on is to decode this mosaic into an image (demosaic) we rebuild an RGB image for display.

Each one of our camera pixels will not have the full 4096 possible tones, measures from DxoMark suggest that the Sony IMX272AQK only resolves 24 bits colours in total and 9 bits of grey tones. So this is why a lossless raw files is only 24.2 MB. This means that an 8K frame video in RAW would be 9.25 MB and therefore a 24 fps RAW video stream would be 222 MB/s or 1,776 Mb/s if we had equivalent compression efficiency. After chroma subsampling to 422 this would become 1184 Mb/s.

Cameras like the ZCam E2 or the BMPCC4K that can record ProRes 422 HQ approach those bitrates and can be considered virtually lossless.

But now we have ProRes RAW so what changes? The CEO of ZCAM has posted an example of a 50 fps ProRes RAW HQ files and this has a bitrate of 2255 Mb/s if this was 24 fps it would be 1082 Mb/s so we can see how my maths are actually stacking up nicely.

Those bit rates are out of reach of almost all memory card so an SSD drive support is required and this is where Atomos comes into the picture.

Atomos have decided to adopt ProRes RAW and currently offer support for Nikon, Panasonic and Zcam selected model.

ProRes RAW workflow

So with the ProRes RAW file at hand I wanted to test the workflow in Final Cut Pro X. Being an Apple codec all works very well however we encounter a number of issues that photographers have resolved a long time ago.

The first one is that RAW has more dynamic range than your SDR delivery space, this also happens with photos however programs work in larger RGB spaces like ProPhotoRGB at 16 bits and using tone mapping you can edit your images and then bring them back to an 8 bit jpeg that is not as good as the RAW file but is in most cases fine for everyone.

Video NLE are not in the same league of photo raw editors and usually deal with a signal that is already video is not raw data. So the moment you drop your ProRes RAW clip on a SDR timeline it clips as you would expect. A lot of work is required to bring back clips into an SDR space and this is not the purpose of this post.

To avoid big issues I decided to work on an HDR timeline in PQ so that with a super wide gamut and gamma there were no clipping issues. The footage drops perfectly into the timeline without any work required to confirm which is brilliant. So RAW for HDR is definitely the way forward.

ProRes RAW vs LOG

My camera does not have ProRes RAW so I wanted to understand what is lost going through LOG compression? For cameras that have an analog gain on sensor there is no concept of base ISO fixed like it happens on Red or ARRI cameras. Our little cameras have a programmable gain amplifier and as gain goes up DR drops. So the first bad news is that by using LOG you will lose DR from RAW sensors.

This graph shows that on the Panasonic GH5 there is a loss of 1 Ev from ISO 100 to 400 but still we have our 11.3 Ev minimum to play with. I am not interested in the whole DR but I just want to confirm that for those cameras that have more DR than their ADC allows you will have a loss with LOG as this needs gain and gain means clipping sooner.

Panasonic GH5 full resolution 20.9 MPixels DR

What is very interesting is that net of this the ProRes RAW file allowed me to test how good is LOG compression. So in this clip I have :

  1. RAW video unprocessed
  2. RAW video processed using Panasonic LOG
  3. RAW video processed using Canon LOG
  4. RAW video processed using Sony LOG

In this example the ZCAM E2 has a maximum dynamic range of 11.9 Ev (log2(3895)) from Sony IMX299CJK datasheet. As the camera has less DR than the maximum limit of the ADC there is likely to be no loss.

We can see that there are no visible differences between the various log processing options. This confirms that log footage is an effective way to compress dynamic range in a smaller bit depth space (12->10 bits) for MFT sensors.

The same ProRes RAW files processed using log from Panasonic, Canon and Sony shows no visual difference

Final Cut Pro gives you the option to go directly to RAW or go through LOG, this is because all your log based workflow and LUT would continue to work. I can confirm this approach is sound as there is no deterioration that I can see.

Is ProRes RAW worth it?

Now that we know that log compression is effective the question is do I need it? And the answer is it depends…

Going back to our ProRes RAW 1082 Mb/s once 422 subsampling is applied this drops to 721 Mb/s this is pretty much identical to ProRes 422 HQ nominal bit rate of 707 Mb/s. So if you have a Zcam and record ProRes RAW or ProRes 422 HQ you should not be able to see any difference. I can confirm that I have compressed such footage in ProRes 422 HQ and I could not see any difference at all.

However typically with photos a RAW files can hold heavy modifications while a JPEG cannot. We are used processing ProRes and there is no doubt that ProRes 422 HQ can take a lot of beating. In my empirical tests I can see that Final Cut Pro X is very efficient manipulating ProRes RAW files and in terms of holding modifications I cannot see that this codec provides a benefit but this may be due to the lack of capability of FCPX.

For reference Panasonic AVC Intra 422 is identical in terms of quality to ProRes 422 HQ though harder to process, and much harder to process than ProRes RAW.

Conclusion

If you have already a high quality output from your camera such as ProRes 422 HQ or Panasonic AVCI 400 Mbps with the tools at our disposal there is not a lot of difference at least for an MFT sensor. This may have to do with the fact that the sensor DR and colour depth is anyway limited and therefore log compression is effective to the point that ProRes RAW does not appear to make a difference, however there is no doubt that if you have a more capable camera, there is more valuable data there and this may be well worth it.

I am currently looking for Panasonic S1H ProRes RAW files. Atomos only supports 12 bits so the DR of the camera will be capped as RAW is linearly encoded. However SNR will he higher and the camera will have more tones and colors resulting in superior overall image quality, someone calls this incorrectly usable DR but is just image quality. it will be interesting to see if AVCI 10 bits and log is more effective than ProRes RAW 12 bits.

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