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Tuesday, August 6, 2013

Misinformation: Sensor Tech

The RAW deal with hot-rodding your camera



Just as with stills, a RAW video file is the unprocessed, uncensored image data that has been captured by the sensor. Largely based on the Live View streams of modern DSLRs, typical video file formats in a DSLR are compressed 8-bit-format files that lose data during the readout process from the sensor, with even more information that's purposefully thrown away when compressing data to conform it to the standards of a DSLR video codec. DSLR manufacturers largely use AVCHD, QuickTime H.264 and AVI (Motion JPEG) as their video file formats because it's ubiquitously understood by electronic devices, which makes the video files simple to view, edit and play back directly from Blu-ray discs or online. Multimedia companies like Panasonic and Sony also have a vested interest in Blu-ray as well as AVCHD, which was codeveloped as a format by the two companies.
 
Myth: Video From DSLRs Is As Good As Cinematic Cameras
 
The problem with 8-bit video is that it's a very "thin" file format. This isn't important when uploading to the web or viewing clips on a television, but in postproduction, this lack of color information can be detrimental for editing, color grading and effects work. 8-bit files only offer 256 shades of red, green and blue color values for each primary color while 10-bit files include 64 times that amount for a larger degree of hues, saturation and brightness. 14-bit files, now available as RAW video in a handful of hacked Canon DSLRs, expand that even further, with a total of 16,384 available tones.

The Magic Lantern firmware add-on, a small piece of software that runs atop the normal Canon DIGIC processing, gives several video-capable Canon EOS cameras plentiful options for video capture. They unlocked video of up to 30 fps frame rates on the 2008 EOS 50D, for example, which included a Live View preview screen, but no video capture capabilities out of the box. (DSLR video is largely captured from the Live View stream.) More recently, they extended this capability in the 50D to RAW video capture, which means that you can now achieve RAW video by purchasing a used $500 camera. In the 5D Mark III, RAW video has been unlocked for much better highlight details and a dynamic range that has increased from 11 stops to 14 stops, comparable to the latitude of film and high-end digital cinema cameras. Sharpness is improved by RAW video, as well.

Magic Lantern is available for the Canon EOS 5D Mark II/III, 50D, 60D, 7D and T3/T3i Rebels, giving them various other professional camcorder abilities, too, including manual audio controls, exposure meters on the Live View screen (like waveform and histogram), as well as focusing tools like precise "follow-focus" control from the camera menu. Still functionalities like internal intervalometer, advanced exposure bracketing and focus stacking are also available. Most recently, Magic Lantern brought the Canon EOS 5D Mark III and 7D a "Dual ISO" mode that makes use of dual ISO amplifiers to capture stills or video at ISO 100 and 1SO 1600 simultaneously for what's essentially in-camera HDR. There's a loss in vertical resolution and the 7D offers stills compatibility only, as the camera hasn't been made capable of RAW video capture. Still, Dual ISO shows what's possible with "hacking." Essentially, these workarounds convert your very affordable DSLR into a cinematic powerhouse capable of many of the features that professional filmmakers use.

The Dual ISO mode also illustrates the potential downsides to hacking your camera, as Magic Lantern warns that the process modifies the standard behavior of the sensor: "Warning - This code changes low-level sensor parameters. In the technical doc you can see how this method messes with the feedback loop for optical black, for example. Therefore, it's safe to assume it can fry the sensor or do other nasty things. My 5D3 is still alive after roughly one week of playing with this, but that's not a guarantee. We don't pay for repairs. Use it at your own risk." Canon hasn't announced an official position on the Magic Lantern hacks, but they do void the warranty of the camera.

 

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