IEEE Consumer Electronics Magazine - April 2017 - 109

8K (7,680 × 4,320)

6K (6,144 × 3,160)

5K (5,120 × 2,700)
4K UHD (3,840 × 2,160)

Cinema 4K

2K (2,048 × 1,080)
HD (1,920 × 1,080)
2K

Cinema 4K
(4,096 × 2,160)

SD (720 × 488)
10 b
at 29.97 fps

FIGURE 1. A visual comparison of image resolution. (Figure courtesy of Coughlin Associates.)

creating HDR images is common with
still-image cameras.
The bit depth is the number of bits
used to indicate the color of a given
pixel in a video frame buffer, or it can be
the number of bits used for each color
component of a single pixel. The bit
depth is often referred to as the color
depth. The color depth is only one
aspect of color representation. It repre-
sents how finely levels of color can be
expressed or the color precision. Gener-
ally, the greater the bit depth of pixels,
the more smoothly the color on one
pixel can shade to the next pixel. Greater
bit depth also adds to the overall storage
capacity required for each video frame.
For example, increasing the bit depth
from 8 b to the 10-b minimum standard
for ultra high definition (UHD) in-
creases the capacity required by 25%.
Figure 3 shows how increasing bit depth
in a fixed number of pixels gives a more
natural look to the resulting image.
The other important aspect of color
representation is how broad a range of
colors is being expressed. This is
called the color gamut. The color space
recorded in a camera is usually a sub-

set of all the colors (light frequencies)
that are sensitive to the human eye
(although some cameras have sensitivi-
ty either at higher or lower light fre-
quencies than to which the human eye
is sensitive). We will talk more about
color spaces later when we discuss con-
sumer displays. In general, professional
video cameras have a very large color
space to which they are sensitive. This
is referred to as a wide color gamut
(WCG). The color encoding specifica-
tion for the camera defines both color
precision as well as the gamut by
assigning a digital code value to a loca-
tion in a color space.
Professional video cameras use an
optoelectronic transfer function that maps
scene luminance to digital code values.
This mapping is generally a logarithmic
function. The log curve generated varies
from one camera manufacturer to anoth-
er because of differences in their camera
image sensors, but it is designed to opti-
mally capture both the details in highly
shaded regions as well as highlighted
regions in a captured scene. The camera
manufacturers make these encoding for-
mulas available to software vendors and

postproduction facilities so they can
restore linear light representations.
Many professional video cameras
also offer RAW recording options that
don't use this logarithmic encoding.
These RAW recordings are very different
between manufacturers, again because of
the different imaging sensors in the cam-
eras. Modern workflows can handle
encoded as well as RAW video images.
RAW image output is larger in the num-
ber of bits per frame than other encoded
video output.

THE SIZE OF CAPTURED
CONTENT
The creation, editing, and distribution of
digital content involve variants of standard
resolution formats. Table 1 shows various
representative characteristics for profes-
sional media standard formats used in
content capture (note that the actual data
rate and storage capacity of working or
archived content can depend upon addi-
tional parameters not discussed in detail
here). A general feature of digital content
is that as the content resolution increases,
the data rate and resulting capacity de-
mand increases as well.
APRIL 2017

IEEE Consumer Electronics Magazine

109

Table of Contents for the Digital Edition of IEEE Consumer Electronics Magazine - April 2017