576i
576i called digital video resolutions with 576 visible lines and interlaced ( interlaced). 576i is a typical resolution for SDTV. At 50 fields per second ( 576i50 ) is compatible with the analog 625/50-Systemen, i.e. all PAL and SECAM types except PAL -M. The picture shape can be both 4:3 and 16:9. In both cases, the pixels are normally square.
"PAL"
Due to the compatibility with the analog 50 -Hertz standards 576i is colloquially referred to as "PAL", such as during a " PAL - DVD". However, this leads to confusion, since no picture PAL format, but an analog Farbkodierverfahren is, which writes the color information than fine patterns in the black and white signal. Such a process is in the digital domain but is usually not used. An exception is an analog PAL signal which has been sampled for later processing at four times the color subcarrier frequency and is stored in this format on the tape. Normally, however, the brightness values and the color difference signals are stored separately from each other.
Compatibility with analog signal
The standard CCIR 601 defines, among other things, a 576i format with 720 pixels per line and 13.5 MHz pixel clock. Just like the analog composite signal is the field rate here is 50 Hz, line frequency 15,625 Hz Furthermore, the composite video signal only 575 visible lines, ie 574 full rows and one half line on the top right and bottom left. The active area of a row, however, is somewhat longer than that of the analog signal at 52 microseconds with 53 ⅓ microseconds. This corresponded exactly 702 pixels. To (horizontal * vertical * frame rate * color depth in bits) to achieve better divisibility in necessary for the digital compression of many codecs 8x8 macroblocks and for the sake of simplicity, a total data rate identical to that of the NTSC digital signal 480i, were these 702 pixels nor to the left and right sides are mostly inactive 9 black pixels added, which gives a total resolution down each row from left to right by 720 pixels with 576 active lines from the top.
A composite video signal can be easily digitized without further format or timing adjustments, such as when the program an analog transmitter digitally transmitted or when a VHS tape to DVD to be copied.
Conversely, a 576i video will be converted into a composite video signal to display it on a PAL or SECAM analog broadcast television or a television station. Here, however, there are losses, especially if the video was produced digitally from the outset: The somewhat broader lines must then trimmed and the additional two half- lines are removed. Furthermore, it comes with the generally poorer shielding of analog antenna and RCA cables to cross- color and cross - luminance artifacts in the image, the brightness channel unintentionally speaks in the color channel, and vice versa., The color resolution is reduced: thus can, for example, for PAL the chrominance subcarrier, only 230 pixel color information per line, and the Y component of the analog YUV signal, which conveys the green or the luminance channel of the image, the color resolution is both PAL and SECAM with halved by mixing each of two lines. It makes sense, therefore, whenever possible, to produce an RGB signal and feed it via Component Video cable into the TV, since they account for the disadvantages mentioned in this way.