YUV

The YUV color model used in analog color television to the standards PAL and NTSC.

Is used to represent the color information of two components, the luminance ( light intensity per unit area, luma ) Y and the chrominance ( color component, chroma), which in turn consists of two sub-components U and V.

General

Just like the color triangle and the derived YUV color model is based on a model with a linear addition of the color stimuli. These models are using a matrix transformed into one another.

When switching to color TV / white signal Searched for technical trails, in addition to black to transfer the color information in order to achieve backwards compatibility with old black / white televisions without having to increase the available transmission bandwidth. The YUV color model of the analog television technology is sometimes mistakenly equated with his relatives YPbPr analog representation and YCbCr for digital display of color video signals, both of which are defined in the standard CCIR 601 or IEC 601.

The analog YUV color model is closely related to the YPbPr analog model or to the digital YCbCr model, but differs in different scaling factors (which are different gain or attenuation factors ) on the color signals. This clearly means that the UV color diagram shown on the right in the YPbPr model in the X- axis or Y -axis is distorted by a certain multiplier to obtain the PbPr color chart. The distribution of colors in the plane is retained. The luminance signal Y is identical in all of these models. The scaling factors for the two color signals are fixed and have the following values:

The reason is that the analog YPbPr model and also the digital YCbCr model spans a symmetrical area in the color level, and thus the two factors Pb and Pr (or Cb and Cr ) are scaled uniformly, which enables easier signal processing. However, the YUV color components U and V are different greatly distorted in the color plane: U is at a lower level is used as V, to give the smallest possible interference with the luminance signal in the quadrature modulating the color sub-carrier in the analog color television.

The color transmission was only developed later for analogue TV, as black / white television sets, which used only the luminance signal Y, were already established on the market. The color television should interfere as the default Black / White receiver only as little as possible. To achieve this, the color signals U and V had to be quadrature modulated with different sizes of amplitude of the color subcarrier, thereby resulting in the distortion factors YUV YPbPr.

The YIQ color model previously used in the NTSC color television standard has as YUV different strength gains for the color channels, which are designated therein as I and Q, even there where since the problem of the least possible disturbance of the already established B / W television had. Additionally carried out at a rotation of the YIQ color plane in the clockwise direction by 33 °. Wherein the color components I and Q are assigned different color values ​​than is the case with the UV, and PbPr CbCr. This rotation circuitry is much more difficult to realize the transition from YIQ to YPbPr and YCbCr digital video, which is why for analog NTSC YUV color model is used since the 1970 's.

Mistakenly is often of YUV ( equipment, cables, coding, color model ) the speech when actually YPbPr ( with analog connections / cables ) or YCbCr is meant ( in the digital domain ). YUV only occurs in the quadrature modulation of the color subcarrier for PAL or NTSC transmission and is otherwise not apply. Also color model is often confused with the color space, a YUV color space, there are no more such as a YPbPr or YCbCr color space.

Principle of the color model

To calculate the luma signal ( also luminance signal) the underlying RGB data is first adjusted with the gamma value of the output device; one obtains a R'G'B signal. The three components are added with different weighting to form the brightness information, which functions as a composite video signal also in old black / white television sets.

The weighting of the components is required, since some aspects of the color vision of the human eye must be considered. For example, green is perceived as brighter red, this in turn brighter than blue. This difference in weight is taken into account in the following ( by definition exact ) conversion formula:

The chrominance ( color difference signals also ) contain the color information. They arise from the difference between the blue component and luminance or red and a luminance and a further reduction. These formulas are exact by definition.

From the three generated components Y, U and V, the individual color components of the primary colors can later be calculated ( the formulas for G are approximate ):

Or

Furthermore, because of the structure of the retina of the human eye, that the brightness information is perceived in a higher resolution than the color, so many building on the YUV color model formats make a reduction in the spatial resolution of the chrominance to save bandwidth during transmission can.

The image resolution is standardized by the Common Intermediate Format (CIF).

• UV - surfaces in a value range of [-1,1]

Y value of 0.5

Y value 1