Deconstructing RAW – Part III

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In this part I’ll take a brief look at raw converters – the software that takes incomplete color and signal data and makes an image out of them.
debayer

From the diagram above, imagine I want to find the green and blue values for the middle red pixel. It should be immediately clear that there are so many ways in which this can be done mathematically. Smart programmers will also see that if one is given access to sufficient metadata, like dynamic range, ambient conditions, etc, one can use that information to make educated guesses on which way to calculate each pixel’s RGB values best.

This is the problem a raw converter needs to solve under the hood. Over and above this, it also needs to provide tools that are easy to understand and still pack a punch when it comes to manipulating data – which is what artists want to do. Not only do these programs have to work in automatic mode, but cater to the whims and fancies of subjective opinions as well.

To compound the problem, each camera manufacturer has their own proprietary raw system, so a good raw converter will have to know exactly what the camera sensor is doing to make the best use of this information.

Some of the important operations performed by raw converters are:

  • White balance
  • Colorimetric interpretation
  • Gamma correction
  • Noise reduction
  • Antialiasing
  • Sharpening

It should be clear that unless the algorithm knows a camera sensor in great detail, it will become very difficult to adequately utilize raw data. E.g., which color space is the sensor in, and what is the gamma setting? What kind of aliasing is present and why is it caused? What kind of sampling method is utilized and how does that affect resolution, contrast and color? The challenges are endless.

With this in mind, let’s take a brief look at some popular raw conversion software:

1

Adobe Lightroom

Adobe Lightroom is the gold standard of still photography raw converters. Even though there are many other programs that compete on a functional level, this program has a unique advantage – it is made by the company that made TIFF – the file standard on which most other file standards are based. Adobe also champions DNG. In today’s marketplace, Lightroom rules.

But that doesn’t mean other programs are worse. We have already seen that raw converters are quirky beasts. Two other heavy hitters in this segment are Phase One Capture-One Pro and DxO Optics Pro. Find the beast you can learn to love.

2

RawTherapee

RawTherapee is open source, multi-platform and free. It is based on dcraw, the free raw format converter. Even so, it has powerful features that might keep most users happy.

Video raw converters have to do everything still raw converters do but also deal with interframe compression and heavy data rates – not to mention dealing with quirky video-centric issues like chroma sub-sampling, field rates, etc.

3

ARRIRAW Converter (ARC)

Most workflows involving the Arri Alexa tend to choose Prores. The ones who stick to Arriraw has to deal with really heavy data rates recorded on to dedicated recorders like Codex, Gemini or S Two, etc. The ARI file is converted to DPX for final processing.

ARC is the raw converter that does this – in case you don’t want to pay for limited and expensive proprietary hardware solutions.

The Arri Converter/SDK has two debayer algorithms – ADA-3 HW (Hardware) and SW (Software) – none of which provide any degree of control except –

  • Sharpness from 0 to 300 (Default 100). This does not correlate to any traditional and professionally used sharpening algorithms.
  • The maximum color bit depth rendered to DPX/TIFF is 10-bit(log)/16-bit(linear) – with no 32-bit float option.

ARC has excellent support for color spaces, but very few ‘dials’ for color control. If I shoot green chroma and need to tweak the green color, I’ll have to use a 3rd party grading application.

ARC basically mirrors the in-built camera (Alexa) controls. It’s like Henry Ford’s famous “any color as long as it is black” policy on the Model-T. But at least it’s free!

One has to wonder if there is any program out there that can truly take full advantage of the data coming out of the Alexa’s sensor. As of now, the options are severely limited.

4

RedCine-X

REDCINE-X is a free application that allows you to view R3D files natively. It also can adjust and manipulate metadata, and has the ability to transcode R3D files to other file formats like DPX, etc.

It has some of the tools one would expect in a raw converter – but not all. However, I suspect it is closely integrated with Red’s cameras, and is able to tweak the raw files from those cameras as best as it can be.

The problem is that it does not offer more than one type of demosaicing algorithm – which is the whole point of a raw converter. At best, Redcine-X is a color grading app to use so clients don’t freak out at the flat looking raw images.

5

CinemaDNG Converters

Even though Cinema DNG has been around for ages, adoption is limited. Two proprietary programs that can debayer DNG are:

Adobe Speedgrade CS6

and

Blackmagic Design DaVinci Resolve

Unfortunately, these too are color grading apps all said and done. Since CinemaDNG files can be created from different cameras using different sensor technology, there is no single solution that covers all cameras.

One could also use a still camera raw converter to batch process DNG files – as long as they are stored as DNG files in a directory structure, as opposed to being wrapped in MXF. But this is a tricky workaround – definitely not for the faint-hearted!

I hope this brief primer has been an eye-opener to the capabilities and pitfalls of using raw files for stills and video work. Choose wisely!

2 replies on “Deconstructing RAW – Part III”

  1. a raw converter does not need to know what gamma or colour space the sensor uses , all sensors use the same colour space ..linear! ..and the same gamma curve .. none!

    colour spaces and gamma are applied later in the process of developing raw images into usable images . any colour space, and any gamma can be applied to any sensor

    please ammend your website , colour science is confusing enough for people

  2. looking and looking for a workflow. I’m using a canon eos m hacked with magic lantern raw. currently I’m using davinci resolve with my cinema dng files. Everything is fine with that but since it’s raw I’m getting tons of noise in the shadows. probably because the sensor is cropping in so much I’m seeing the noise amplified. I can get the footage looking really good if I apply neat video but it takes forever. Also I’m trying to ettr as much as I can. Any raw program out there that has noise reduction as good as neat video but much faster?

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