Hanover bars: Difference between revisions
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{{Short description|Undesirable visual artifact in television}} | {{Short description|Undesirable visual artifact in television}} | ||
[[Image:Hanoverbars without PAL delay.png|thumb|Simulated strong Hanover bars shown on a [[Philips circle pattern|Philips PM5544]] [[Test card|test pattern]]. Note: Hanover bars can only be seen by viewing full-size image]] | [[Image:Hanoverbars without PAL delay.png|thumb|Simulated strong Hanover bars shown on a [[Philips circle pattern|Philips PM5544]] [[Test card|test pattern]]. Note: Hanover bars can only be seen by viewing the full-size image]] | ||
[[Image:Hanover_bars_with_PAL_delay.png|thumb|Simulated cancellation of Hanover bars through a chroma delay line]] | [[Image:Hanover_bars_with_PAL_delay.png|thumb|Simulated cancellation of Hanover bars through a chroma delay line]] | ||
'''Hanover bars''', in one of the [[PAL]] television [[video]] formats, are an undesirable visual artifact in the reception of a television image.<ref>{{Cite web|url=https://www.radiomuseum.org/forum/45_years_anniversary_of_walter_bruchs_pal_color_television.html|title=45 Years Anniversary of Walter Bruch's PAL Color Television|website=www.radiomuseum.org}}</ref><ref name="auto">{{Cite book|url=https://books.google.com/books?id=U9aH92iLEZAC&dq=Hanover+bars+pal+-wiki&pg=PA112|title=TV and Video Engineering|first=A. M.|last=Dhake|date=May 1, 1999|publisher=Tata McGraw-Hill Education|isbn=9780074601051 |via=Google Books}}</ref> The name refers to the city of [[ | '''Hanover bars''', in one of the [[PAL]] television [[video]] formats, are an undesirable visual artifact in the reception of a television image.<ref>{{Cite web|url=https://www.radiomuseum.org/forum/45_years_anniversary_of_walter_bruchs_pal_color_television.html|title=45 Years Anniversary of Walter Bruch's PAL Color Television|website=www.radiomuseum.org}}</ref><ref name="auto">{{Cite book|url=https://books.google.com/books?id=U9aH92iLEZAC&dq=Hanover+bars+pal+-wiki&pg=PA112|title=TV and Video Engineering|first=A. M.|last=Dhake|date=May 1, 1999|publisher=Tata McGraw-Hill Education|isbn=9780074601051 |via=Google Books}}</ref> The name refers to the city of [[Hanover]], in which the PAL system developer [[Telefunken|Telefunken Fernseh und Rundfunk GmbH]] was located. | ||
The PAL system encodes color as ''[[YUV]]''. The ''U'' (corresponding to ''[[B-Y]]'') and ''V'' (corresponding to [[B-Y|''R-Y'']]) signals carry the color information for a picture, with the [[phase (waves)|phase]] 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 (waves)|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.<ref>{{Cite book|url=https://books.google.com/books?id=pY2jBQAAQBAJ&dq=Hanover+bars+pal+-wiki&pg=PA71|title=Newnes Guide to TV and Video Technology|first=Eugene|last=Trundle|date=May 12, 2014|publisher=Elsevier|isbn=9781483183169 |via=Google Books}}</ref> | The PAL system encodes color as ''[[YUV]]''. The ''U'' (corresponding to ''[[B-Y]]'') and ''V'' (corresponding to [[B-Y|''R-Y'']]) signals carry the color information for a picture, with the [[phase (waves)|phase]] 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 (waves)|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.<ref>{{Cite book|url=https://books.google.com/books?id=pY2jBQAAQBAJ&dq=Hanover+bars+pal+-wiki&pg=PA71|title=Newnes Guide to TV and Video Technology|first=Eugene|last=Trundle|date=May 12, 2014|publisher=Elsevier|isbn=9781483183169 |via=Google Books}}</ref> | ||
Latest revision as of 06:25, 18 October 2025
Hanover bars, in one of the PAL television video formats, are an undesirable visual artifact in the reception of a television image.[1][2] The name refers to the city of Hanover, in which the PAL system developer Telefunken Fernseh und Rundfunk GmbH was located.
The PAL system encodes color as YUV. The U (corresponding to B-Y) and V (corresponding to R-Y) signals carry the color information for a picture, with the phase 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.[3]
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.[4] This causes phase errors to cancel out, at the cost of vertical color resolution, and in early designs, also a loss of color saturation proportional to the phase error.[2]
References
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