Digital Signal Processing Reference
In-Depth Information
Each pixel has a red (R), green (G) and blue (B) component.
There are other ways to describe this as well, but we will look at
red, blue and green first. Let's say that you use eight bits to store
the value of red, eight bits for blue and eight bits for green. With
eight bits you can have 2
8
or 256 different possible values for red,
blue and green each. When this is the case, people refer to this as
a color depth of eight, or an 8-bit color depth.
Some HD video will be encoded with 10-bit color depth or
even 12-bit color depth
e
each RGB component is encoded with
10 or 12 bits.
While more is better, remember that these bits add up.
Consider 8-bit color depth. Each pixel requires 8
3
24 bits to
¼
represent its value.
Now think about a flat-panel TV in your house. You probably
remember that this TV is 1080p
the salesperson probably also
e
talked about 1920
1080 resolution. What this means is that each
video frame shown on this flat-panel TV has 1080 lines and that
each line has 1920 pixels. So you were already talking about pixels
all the time
even though it may not have registered.
Let's put it together. Since each pixel requires 24 bits, and
there are 1920 pixels per line and there are 1080 lines in one frame
of video, this means that your hard-working flat-panel TV is
showing you information that is 24
e
49,766,400
bits in each frame. Approximately 50 million bits; also referred to
as 50 Mbits. And remember most TVs go through 60 frames in one
second. Some of the newer ones even go through 120 fps.
So to give you the viewing pleasure for one second we have to
manipulate 3 billion bits, also referred to as 3 Gbits. And this is
with 60 fps with a color depth of 8
1920
1080
¼
It could be higher.
Table 2.1
shows the number of bits required for each frame at
different resolutions. Here we have used 30 bits per pixel and also
.
Table 2.1
Frame Size: (Total # of
Pixels)
Frame Size: (Assume
30 Bits per Pixel)
Image Size
1920
1080p
1920
1080 = 2 M pixels
60 Mbits
1920
1080i
1920
1080
0.5 = 1 M
pixels
30 Mbits
1280
720p
1280
720 = 900 K pixels
27 Mbits
SD720
480p
720
480
0.5 = 173 K
pixels
5.19 Mbits
