Specifications
8
Note: The exposure axis of these figures has a zero label to indicate the luminance of a mid-gray
object when lit for ISO 320. Speed rating of digital cameras (or film for that matter) is an area
of some debate. The “normal” exposure reference was based on the shape of the REDspace™
Gamma option (i.e. the camera default setting), the 320 ISO exposure recommendation in the
camera user manual, as well as technical standards in this area. When shooting film, one essentially
picks a “sensor” depending on the expected lighting situation. With the RED, one has a sensor with a
fixed speed and makes a noise trade-o in post-production, not unlike pushing a film stock. This
trade-o is made via the ISO or Exposure settings. (It is our understanding that changing the
ISO setting on the RED camera does not aect capture, only post-processing.)
Figure 2. By manually subtracting the pixel
value from a shot with the lens cap on, we
got Figure 2. This shows a response that is
indeed nearly linear with respect to scene
luminances. The camera specifications
claim a 12-bit A/D converter, and indeed,
we see almost 12 stops of dynamic range
between black and the clipping point. It is
worth noting that, although this response
can be measured in a laboratory setting,
with appropriate pixel averaging, the
bottom three to four stops of dynamic
range are quite noisy and may be of limited
use for real-world image capture. Indeed,
as we will see next, most of the gamma
setting options compress this part of the
tone scale heavily.
Figure 1. The result of setting
gamma to Linear. This graph
shows some residual dark
current, since the minimum
pixel value is about 800 (out of
65535). The behavior near black
is dependent upon the black
shading operation, which is done
as part of the camera calibration.
We ran the black shading several
hours before this part of our
testing was done, and the camera
dark current may have risen during
that time.