Non-linear contrast control apparatus with pixel distribution measurement for video display system

• US 5,422,680 A
• Filed: 08/24/1994
• Issued: 06/06/1995
• Est. Priority Date: 05/22/1992
• Status: Expired due to Term

• Current Assignee: Thomson Consumer Electronics Incorporated (Vantiva SA)
• Original Assignee: Thomson Consumer Electronics Incorporated (Vantiva SA)
• Inventors: Bergen, James R., Pica, Albert P., Lagoni, William A., Christopher, Todd J.
• Primary Examiner(s): Groody, James J.
• Assistant Examiner(s): HSIA, SHERRIE Y
• Application Number:
  US08/296,074
• Time in Patent Office: 286 Days
• Field of Search: 348/615, 348/674, 348/625, 348/671, 348/687, 348/678, 348/675, 348/630, 358/163, 358/164, 358/166, 358/168, 358/169, 358/174, 358/32, 358/37
• US Class Current: 348/674
• CPC Class Codes: H04N 5/20 Circuitry for controlling amplitude response

Abstract

A video signal to be processed is applied to a non-linear processor having an adjustable gain responsive to a control signal over at least one portion of the amplitude range of the video input signal. A sampling circuit, responsive to the video signal, generates video samples related to the video signal. A control circuit, responsive to the video samples, generates the control signal in accordance with the number of samples in at least a given amplitude range thereby controlling the percentage of samples of a given range in displayed images. Plural control and sampling circuits may be included provide control for white stretch processing, black stretch processing and video mid-point processing for enhancing contrast through out the entire video signal range.

Claims

1. A video signal processing system for use in a given apparatus, comprising:

first means responsive to a given one of a video input signal and a video output signal of said system supplied thereto for generating a count representative of the total number of picture elements that occur within a given time interval of at least one field interval of said given video signal and which have video signal levels that lie within a predetermined range of values with respect to a given video reference level;

second means for comparing the count of said first means with a given percentage of the total number of the picture elements occurring within said given time interval for generating a control signal;

controllable means, having a controllable transmission characteristic and having a control input to which said control signal is applied for altering the transmission characteristic of said video input signal supplied to said controllable means in a sense to said form a video output signal representative of images having selected response characteristics controlled as a given function of said count; and

wherein;

said given apparatus comprises a television picture reproducing apparatus;

said use in said apparatus comprises contrast modification of the images produced by said apparatus;

said contrast modification is non-linear for altering the contrast of areas of one brightness level of said images differently than areas of another brightness level;

said predetermined range of values comprises values equal to or less than said given video reference level;

said controllable means comprises a non-linear transfer function generator having an input coupled for receiving said video input signal;

said given video signal applied to said first means is taken from said video output signal produced by said non-linear transfer function generator for causing said video signal processing system to be subjected to feedback control of the contrast of said video output signal so as to provide a predetermined percentage of black pixels in displayed images.

2. A non-linear video signal processor, comprising:

a non-linear transfer function generator (12) having an input (14) for receiving a video input signal (Y1) to be processed and having an output (16) for providing a processed video output signal (Y2), said non-linear transfer function generator having a control input (18) for receiving a control signal (S1) for controlling the transfer function of said non-linear transfer function generator;

a pixel distribution measurement circuit (20) having an input (22) connected to said output (16) of said non-linear transfer function generator (12) and having an output (28) for providing a pixel distribution indicating signal (S2) representative of a percentage of black level pixels in said processed video output signal (Y2); and

a control signal generator (30) having an input connected to receive said output (28) of said pixel distribution measurement circuit and having an output connected to supply said control signal (S1) to said control input (18) of said non-linear transfer function generator (12) for regulating the percentage of black level pixels in said processed video output signal (Y2).