2. YUV
• The Y'UV model defines a color space in terms of
one luma (Y') and two chrominance (UV)
components.
•
• The Y'UV color model is used in the PAL and
SECAMcomposite color video standards.
•
• Previous black-and-white systems used only luma
(Y') information.
•
3. YUV
• Color information (U and V) was added
separately via a sub-carrier so that a black-
and-white receiver would still be able to
receive and display a color picture
transmission in the receiver's native black-
and-white format.
4. The Digital Video Signal or YUV
• YUV has basically three components:
• the luminance or green channel (Y),
• the colour value of the luminance deducted from the
colour red (R-Y),
• the colour value of the luminance deducted from the
colour blue (B-Y).
• When digitised, these three parameters of the
component video signal are assigned a numeric value.
• The groupings and Interpolation order of these values
from the sensor determine the resolution and colour
density of the camera’s output.
5. Y Cb Cr
• YCbCr, Y′CbCr, or Y Pb/Cb Pr/Cr, also written
as YCBCR or Y′CBCR,
• Y′ is the luma component and CB and CR are
the blue-difference and red-difference chroma
components. Y′ (with prime) is distinguished
from Y which is luminance, meaning that light
intensity is non-linearly encoded using gamma
correction.
6. LUMA IN YCbCr
• Luma is carried in the Y ’ channel.
• Since the eye is more sensitive to changes in
luma than to changes in colour, the two colour
difference channels are usually encoded with
less information than the Luma channel, and
various image formats are bandwidth limited,
employing chromasubsampling to encode
more or less colour information ( example
4:2:2, 4:2:0, 4:1:1).
7. • However, all video formats, regardless of the
chroma sampling scheme they employ,
encode the full amount of luma.
9. LUMA IN RGB
• The RGB colour model is followed by Kodak
Cineon and DPX sequence formats, which are
used from both film scanning and digital
cinema camera acquisition. RGB is also used
by Sony HDCAM SR video format, as well as by
an increasing number of raw colour space
formats used by digital cinema camera such as
the RED ONE and ARRI Alexa.
10. • RGB image formats encode discrete colour
component channels for red, green, and blue
image data. These formats typically encode
the full sampled amount of each colour, with
no chromasubsampling, although various
acquisitions or distribution formats may
employ spatial or temporal data compression.
11. Subsampling
• Chromasubsampling is the practice of
encoding images by implementing less
resolution for chroma information than for
Luma information. Taking advantage of the
human visual system’s lower acuity for colour
differences than for Luminance. It is used in
many video encoding schemes – both
analogue and digital and also in JPEG
encoding.
13. Subsampling Ratio Example 4:2:2:4
• 4:2:2:4
• 4: Luma horizontal sampling reference
• 2: Cb and Cr Horizontal factor
• 2: Same as second digit; or zero, indicating
Cb and Cr are sub-sampled 2:1 vertically
• 4: If present, same as luma digit; indicates
alpha (key) component
14. XDCAM Subsampling Ratios 4:2:0
• 8 -bit Linear
Sampling Ratio 4:2:0
No colour in the second channel, this means
green screen work will be harder to achieve.
15. Sampling Ratio 4:1:1
• This interpolated HD sampling scan rate is
commonly referred to as 4:1:1
• This means there are four luminance or green
pixels to every one each red and blue
pixel, which hold the colour information for a
shot.
•
17. Sampling Ratio 4:2:2: (2/4)
• This interpolated HD sampling scan rate is
commonly referred to as
• This means there are four luminance or green
pixels to every two each red and blue
pixel, which hold the colour information for a
shot.
•
• FOR TRUE HD GREEN SCREEN
PRODUCTION, YOU NEED A 4:2:2 CAMERA.
20. Sampling Ratio 4:4:4
• This interpolated HD sampling scan rate is
commonly referred to as
• This means there are four luminance or green
pixels to every four each red and blue
pixel, which hold the colour information for a
shot.
•
• Perfect for all post production.
