[54] IMAGE SIGNAL AVERAGE PICTURE LEVEL DETECTING APPARATUS
[75] Inventors: Atsuhisa Kageyama, Ibaraki; Hideaki Sadamatsu, Hirakata, both of Japan
[73] Assignee: Matsushita Electric Industrial Co., Ltd., Osaka, Japan
[21] Appl. No.: 728,245
[22] Filed: Jul. 10,1991
[30] Foreign Application Priority Data
Jul. 19, 1990 [JP] Japan 2-189471
[51] Int. CV H04N 9/27; H04N 5/235;
H04N 5/57; H04N 5/18
[52] U.S. CI 358/139; 358/39;
358/168; 358/172; 307/494
[58] Field of Search 358/160, 21 R, 39, 139,
358/10, 168, 170, 171, 172, 173, 27, 34, 169;
307/491, 358, 494
[56] References Cited
U.S. PATENT DOCUMENTS
3,569,620 3/1974 Baun 358/170
4,338,527 7/1982 Nagano 307/494
4,340,904 7/1982 Wingrove, Jr 358/29
4,543,614 9/1985 Chen 358/193.1
4,691,235 9/1987 Okui et al 358/172
5,162,902 11/1992 Bell et al 358/168
FOREIGN PATENT DOCUMENTS
49023 6/1966 Fed. Rep. of Germany . 1451830 10/1976 United Kingdom .
Primary Examiner—James J. Groody
Assistant Examiner—Safet Metjahic
Attorney, Agent, or Firm—Wenderoth, Lind & Ponack
[57] ABSTRACT
The average picture level (APL) of a video luminance signal is detected, wherein the output of a first current mirror circuit used as the load of a differential amplifying circuit is fed into a smoothing circuit via a second current mirror circuit. The direct current voltage of the output and the detection voltage amplitude may be optionally set without causing an offset voltage in the output average picture level voltage, with the current flowing through the second current mirror circuit being made zero at the time of APL=0%.
3 Claims, 6 Drawing Sheets
