7. DVD Color Conversion.
Color information recorded in the color palette provided by each PGC is encoded
as luminance and color difference coded signals (YCrCb). This encoding is popular
among many component video systems and is used by the DVD-Video standard.
YCrCb is the method of color encoding for transmitting color video images while
maintaining compatibility with black-and-white video. This type of encoding has
traditionally been used in composite television. This method uses less bandwidth
than the three separate video signals in an RGB video transmission in computers.
Compression algorithms can achieve high degree of compression with YCrCb encoding.
YCrCb consists of two major components: luminance (Y) and chrominance (CrCb or also
known as UV). Luminance describes the black-and-white component of a video signal
(pixel color). The amount of luminance or Y-component of a video signal indicates
its brightness (the amount of light intensity). Certain amount of luminance is required
to make a color pixel visible to the human eyes. Chrominance (or chroma) describes
the color portion of the video signal which includes hue and saturation information.
Hue indicates the color tint of an image. Saturation describes the condition where
the output color is constant, regardless of changes in the input parameters.
The chrominance components of YCrCb include the color-red (Cr) component and
the color-blue (Cb) of the color.
Digital coding in the form of YCrCb signals can represent a substantially
greater gamut of signal values than can be supported by the corresponding ranges
of RGB signals. Therefore, it is possible to produce YCrCb signals which would
result in out-of-range values when converted to RGB. To prevent overflowing
conditions, clipping is applied to the YCrCb signals before performing the RGB
conversion. Clipping can be applied in a way that maintains the luminance and hue
values and minimize the subjective impairment by sacrificing only saturation.
The following on-line tools can be used to convert between the two color spaces,
YCrCb to RGB and vice versa.
There are different equations for SDTV
(Standard Definition Television,
525-line and 625-line systems) and HDTV
(High Definition Television, 1920 by 1080
resolution). The equations differ only in the coefficients.
The following color conversion for SDTV uses the coefficients as recommended by the
BT.601-5 standard for 4:3 and wide-screen 16:9 aspect ratios
and is most compatible with the usage of DVD colors on standard televisions.
YCrCb to RGB (SDTV)
RGB to YCrCb (SDTV)
The following color conversion for HDTV uses the coefficients as recommended by the
BT.709-5 standard for HDTV
and is most compatible with DVD colors on computer
monitors and high-definition televisions.
YCrCb to RGB (HDTV)
RGB to YCrCb (HDTV)
Information regarding the conversion equations and their coefficients to convert from
YCrCb to RGB color space and vice versa are explained in The
Unofficial DVD specifications 2.2
. This ebook is now available in Adobe Acrobat
PDF format. If you do not have a permanent Internet connection, this ebook can save
you a lot of connection time by reading it off-line and it contains more information
than presented on the web pages. Each DVD instruction is organized as a bookmark so
you can get to the desired page of any of the 36 DVD commands with just a click.
All research efforts have been done for you and summarized in an easy-to-read format.