ARRI ARRIFLEX D-21 - Manual (Page 15)

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ARRI | ARRIFLEX D-21 / D-21 HD
Different Productions Require Different Outputs
Different projects have different production requirements, budgets and distribu-
tion channels; the equipment chosen has to be flexible enough to accommodate
those differences. The unique construction of the ARRIFLEX D-21 and D-21
HD allows for various output signals to be generated, accommodating diverse
production needs and pipelines.
Both the D-21 and the D-21 HD are capable of generating the Mscope signal,
as well as a number of HD signals. HD output options include 'Linear' or Loga-
rithmic output, 4:2:2 YCbCr or 4:4:4 RGB, Normal or Extended Range, as well as
an optional fiber optic link. These output formats are well established standards
that integrated the cameras seamlessly into the existing HD infrastructure.
Additionally, the D-21 is capable of generating a raw data signal that can be
output concurrently with the HD signal. The uncompressed, 12 bit raw Bayer
data from the D-21's 4:3 sensor is thus available in full resolution. The ARRIRAW
T-link (Transport Link) is a method of transporting the ARRIRAW data over a
standard dual link HD-SDI connection. The data files which result from process-
ing of the ARRIRAW recordings are as easy to grade as those scanned from film
because they have the same pixel raster and colorimetry as film scans.
ARRIRAW T-Link
One of the obstacles that has held back the use of raw data in the past has been the problem of how
to get data easily from the camera to a recorder. ARRI engineers have found a way to utilize a standard
dual link HD-SDI connection to transport the raw D-21 Bayer data. This transport method is called "AR-
RIRAW T-Link" (Transport Link). It allows any recorder capable of recording an uncompressed dual link
HD-SDI stream to record raw D-21 Bayer data, greatly simplifying the raw data workflow for manufac-
turers and users alike. The properties of the dual link HS-SDI connection are defined in SMPTE 372M.
The standard specifies a maximum data rate of 2.97 Gb/s, which is enough bandwidth to carry the 12
bit D-21 raw Bayer data. SMPTE 372M also defines a number of standardized source signal formats to
be sent through two BNC cables (affectionately known as Link A and Link B).
One of those source signal formats is the RGBA format. RGBA stands for red, green and blue plus an
alpha channel, technically called 4:4:4:4 (R'G'B'+A)/10 bit. The ARRIRAW T-Link works by mapping the
12 bit raw Bayer data into this RGBA data stream, so that it can be transported via a dual link HD-SDI
connection.
Any recorder that is capable of recording a SMPTE 372M compliant RGBA signal and playing it back
without compression or further encoding can record this signal. If the signal is recorded by a data re-
corder, the additional option of a live preview exists. The data recorder can extract the original D-21 raw
Bayer data out of the RGBA data stream, and use a real-time image reconstruction algorithm to display
the 4:3 image as a 1440 x 1080 preview HD image. If anamorphic lenses are used on the D-21 a suitably
"de-squeezed" image can be displayed on an HD monitor.
A similar but more refined process is used in postproduction. The original raw Bayer data is extracted
from the RGBA stream, and advanced image reconstruction algorithms are used to reconstruct a
pristine image in HD, 2K or 2.8K. Doing this in post has the added advantage that it does not have to
be done in real-time, so a significantly better image quality and greater flexibility are possible. Note that
throughout the whole process, the image always stays uncompressed, at the highest quality.
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Data recorders that can
record and play back the
ARRIRAW T-Link signal
can be certified by ARRI.