1 The Director of Photography – an overview

94 Practical Cinematography
1-bit 0 (or 1)
2 � 2 values
2-bit 0 1
2 � 2 � 4 values
4-bit 0 1 0 1
2 � 2 � 2 � 2 � 16 values
6-bit 0 1 0 1 0 1
2 � 2 � 2 � 2 � 2 � 2 � 64 values
8-bit 0 1 0 1 0 1 0 1
2 � 2 � 2 � 2 � 2 � 2 � 2 � 2 � 256 values
10-bit 0 1 0 1 0 1 0 1 0 1
2 � 2 � 2 � 2 � 2 � 2 � 2 � 2 � 2 � 2 � 1024 values
12-bit 0 1 0 1 0 1 0 1 0 1 0 1
2 � 2 � 2 � 2 � 2 � 2 � 2 � 2 � 2 � 2 � 2 � 2 � 4096 values
Figure 9.1 The effect of adding
more bits to the binary code
used to write four combinations, with each combination representing
one value.
The great advantage of this system is that one can easily design a
machine, or electronic circuit, to recognize this code, as we can tell it
one is represented by ‘On’ and zero is represented by ‘Off’. So, as we
are only asking our machine to tell if it is on or off to understand all
the numbers we require, we have gained a huge advantage – we can
copy our string of codes as many times as we like, with absolute accuracy,
and even the most stupid of machines can tell if it is on or off.
Here lies the advantage of digital copying over photographic copying;
every time you make a photographic copy there will be some loss
in quality, no matter how small, but every digital copy should be an
exact replica of the original. We can now, therefore, make as many
copies, or intermediates, as we wish.
But how many combinations of zeros and ones should we assign to
each pixel to get an exact representation of our photographic original?
Well, perceived wisdom tells us we need 10 or 12 combinations of zeros
and ones in order that the digital intermediate process remains seamless.
Figure 9.1 shows how the number of combinations available with
different numbers of zeros and ones moves up to an astounding 4096
for 12-bit encoding.
Linear and logarithmic sampling
There is a way of encoding the original scanning of the camera negative
that can both make the picture more appealing to the eye and, at
the same time, reduce the size of the digital files used to store the
images. It involves the use of logarithmic sampling rather than the traditional
linear sampling.