Hanover bars, in one of the

PAL Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...

television

video Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) syst ...

formats, are an undesirable visual artifact in the reception of a television image. The name refers to the city of

Hannover Hanover (; german: Hannover ; nds, Hannober) is the capital and largest city of the German state of Lower Saxony. Its 535,932 (2021) inhabitants make it the 13th-largest city in Germany as well as the fourth-largest city in Northern Germany ...

, in which the PAL system developer Telefunken Fernseh und Rundfunk GmbH was located. The PAL system encodes color as ''

YUV YUV is a color model typically used as part of a color image pipeline. It encodes a color image or video taking human perception into account, allowing reduced bandwidth for chrominance components, compared to a "direct" RGB-representation. H ...

''. The ''U'' (corresponding to ''

B-Y B-Y indicates a color difference signal between Blue (B) and a Luminance component, as part of a Luminance (Y) and Chrominance (C) color model. It has different meanings depending on the exact model used: *U in YUV, a generic model used for analo ...

'') and ''V'' (corresponding to ''R-Y'') signals carry the color information for a picture, with the

phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform * Phase space, a mathematic ...

of the ''V'' signal reversed (i.e. shifted through 180 degrees) on alternate lines (hence the name PAL, or ''phase alternate line''). This is done to cancel minor phase errors in the reception process. However, if gross errors occur, complementary errors from the ''V'' signal carry into the ''U'' signal, and thus visible stripes occur. Later PAL systems introduced alterations to ensure that Hanover bars do not occur, introducing a ''swinging burst'' to the color synchronization. Other PAL systems may handle this problem differently.

Suppression of Hanover bars

To suppress Hanover bars, PAL color decoders use a delay line that repeats the chroma information from each previous line and blends it with the current line. This causes phase errors to cancel out, at the cost of vertical color resolution, and in early designs, also a loss of

color saturation Colorfulness, chroma and saturation are attributes of perceived color relating to chromatic intensity. As defined formally by the International Commission on Illumination (CIE) they respectively describe three different aspects of chromatic ...

proportional to the phase error.

Suppression of Hanover bars

References

See also