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Video signal processing

5  Video signal processing

5.1  General

The general way of encoding light captured from a scene (with a camera) to a video signal, which
serves as input for a display unit, can be described by the following steps:

•  Step 1: Light from the scene is captured and transferred to linear RGB. This conversion occurs

with a given color gamut and white point.

•  Step 2: The linear RGB signal is transferred to a perceptual uniform R’G’B’ video signal. This is

called the gamma correction.

•  Step 3: The color channels can be encoded. The encoding transforms the R’G’B’ video signal to

an Y’C

b

C

r

 video signal to optimize stream capacity. Often a 4:2:2 chroma subsampling is per-

formed. This conversion is not always performed and unencoded R’G’B’ 4:4:4 can be transmitted
as e.g. Dual link HDSDI or 3Gb/s SDI.

Each step is defined by a standard (e.g. Rec.709) The different standards used in the different
steps are listed in the table below:

 Table 2: Standards used for video signal generation

480i: SMPTE RP145 

576i: EBU 3213

Rec.709

SMPTE RP145

Rec.709

Rec.709

SMPTE 240M

ITU-R BT.601 (Rec. 601) Rec.709

SMPTE 240M