Raw movie
Raw film ( engl . Rohfilm ) is an uncompressed video format . Here, the raw data that the sensor reads is uncompressed and moved into a separate container, depending on the camera manufacturer. As in the raw data format in photography , the raw format is very data-intensive when filming.
Raw Debayer
In order to be able to display a raw film format on the computer, so-called debayer is required . These are converters that use metadata to transcode the raw data stream from the digital film sensor into a playable video format. Raw film formats are not film formats, but are files made up of information that the sensor has passed on. It is the digitally converted image of a film sensor at a certain point in time of its exposure (see also digital negatives ).
Raw movie metadata
The metadata are mostly saved in XML metadata format so that they can be used for debayering during post-production. If a change is made during post-production, such as the white balance of the raw film recording, this is only saved in the associated XML and is therefore available to all further debayers of other editing programs.
Video formats
Common video formats use a so-called chroma subsampling to save data rates . Here, from the RGB-signal of the chip derived three signals:
- Y, the luma value: The brightness values of the sensor are read out here. This is the most important signal for the human eye
- CB, the blue chrominance signal
- CR, the chrominance signal red
Subsampling
In order to save further data, the graduated signals (CB and CR signal) are recorded with a lower sampling rate. This results in video signals with, for example, 4: 2: 2 subsampling. Since the human eye is very sensitive to brightness, the sampling rate of the Y signal should never be reduced, as this would make the image appear blurred and dull. The Canon EOS 5D Mark II and its successor, for example, only offer 4: 2: 0 subsampling as a compressed H264 container format.
Color depth
Because a raw movie is an uncompressed format, the footage is not corrupted by subsampling. This depends on the quality of the film sensor chip and its components for data stream generation. The R3d- Raw of a Red Epic Dragon camera, for example, offers a color depth of 16 bits per RGB channel . In contrast to a 4: 4: 4 format, you also have to use a color depth of 16 bits per color channel (2 to the power of 16, i.e. 65,536 color gradations per channel) in post-production. Especially with color gradients, this prevents the so-called puddle formation, which can result from over-sampled film recordings in digital post-production. A raw film is much more sensitive to the smallest changes in the color balance, which pays off in color grading and fine adjustment.
Dynamic range
The high accuracy due to the high bit depth results in an increased dynamic range. The dynamic range of a raw film recording is many times higher than that of a compressed recording. The lighter and darker image contents are reproduced within the raw film recording and the information is not lost through excessive subsampling. New HDR televisions are also playing an increasing role here, as they can display the high dynamic range of such a raw recording for the first time in home cinema. HDMI 2.0a already supports the information spectrum for HDR film.
History of Raw Film
The negative film is preferred to the digital medium by many film producers because it offers the greatest dynamic range . Until the appearance of Red One in 2007, Hollywood digital cine cameras were only ridiculed and the big camera manufacturers such as ARRI did not deal with the topic of digital chips. The appearance of the Red One changed this because the workflow was significantly simplified and the development costs for the negative film were completely eliminated. What is being filmed can be viewed directly on set, which is a great advantage.
Individual evidence
- ↑ Marc Sauter: HDR for television. HDMI 2.0a supports high dynamic range. Golem.de , April 9, 2015. Retrieved April 13, 2015.