Silicon Imaging SI-2K, Руководство пользователя

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ShootingwiththeSI-2K
SI 2K Manual
Note: The exposure controls monitor the RAW 10-bit log data, not the modifi-
cations of a .look file 3D LUT. This is so the D.P. can see the effects of exposure
on his digital negative, providing as much information as necessary to get the
look desired rather that accidentally clipping data because the .look 3D LUT
was higher-contrast and masking valuable information to maintain a proper ex-
posure at the RAW data level.
Nominal Exposure Control
The RAW 10-bit log curve of the SI-2K camera delivers over 11 f-stops of
dynamic range. By nominally exposing the native log curve at an ISO of 320
under a 3200K light-source and 250 under a 5600K light-source, 4.7 f-stops
of dynamic range can be visualized between an 18% middle grey card and the
highlight clip point. An additional 5.6 f-stops is available below the middle-grey
point using this exposure setting. Additionally these settings should set the
18% grey card to a luminance of 40% per the ITU-R709 specification for an
18% grey card reflectance value.
Because the SI-2K shoots RAW digital information and preserves the entire
dynamic range of the sensor data for the end-user, the SI-2K has a nominal
ISO value for a given 18% grey-card reflectance value, but not a “fixed” ISO
value. Should the dynamic range of a scene require less than 4.7 f-stops be-
tween middle-grey and white-clip, the D.P. can decrease the ISO of the camera,
rating it at ISO 200 or 160, etc. in order to gain signal-to-noise ratio basically
pushing more data to the “top” of the dynamic range curve where there is
less noise in the signal. When rated at ISO 160 under a 3200K light-source
for instance, the camera will have only 3.7 f-stops between an 18% grey card
exposed at 40% luminance and 100% white-clip, 1 f-stop less than at ISO400,
but the overall noise-level of the signal will be reduced. Alternatively one can
expose an 18% grey card at 50% reflectance, and this will have the same net
effect as rating the camera at ISO 160.
Note: In the mid-tones there is approximately a 12% reflectance meter dif-
ference for 1 f-stop of exposure change. This value changes slightly as one
exposes towards the extremes of the curve.
Exposing with the Histogram
To achieve the best exposure for a given scene, and preserve the maximum
amount of clean data in the RAW “digital negative”, one should try to expose
“to the right” on the histogram.
The on-screen histogram in the SI-2K represents a distribution graph of the
amount of all the values in a scene. Moving towards the left of the histogram
describes darker values, while moving towards the right of the histogram de-
scribes lighter values. At either end is the maximum and minimum values that
can be stored in a 10-bit encoded file. The height of a given point on the histo-
gram describes the amount of pixels exposed at a given value along the 10 bit
scale. When more pixels in a scene are exposed at a given value, the graph is
taller at that point.