FR2648660A1 - METHOD AND CIRCUIT FOR DECREASING COLOR SHINING - Google Patents

Abstract

Method and circuit characterized in that the color difference signals created by the decoding are subjected to a controlled recursive filtering and to the circuit for carrying out the method where the outputs are connected by a multiplexer to a noise reduction system 4 , 12, 13 digital comprising a recursive filter 4 controlled and in that the output of the recursive filter is applied by a digital / analog converter 14 to the demultiplexer for the other processing stages.

Description

Method and circuit for reducing flicker

colours ".

  The present invention relates to a method for reducing color flickering when reproducing color video signals for color difference signals transmitted

sequential online.

  The invention also relates to a circuit

  for the implementation of this process.

  In sequential color television methods (for example SECAM) to reduce the transmission capacity of the chrominance channels, the two color difference signals R-Y and B-Y are transferred sequentially per line. To restore RGB signals for display on a color television receiver, color difference signals must again be made simultaneous in an appropriate decoder using line memory. This means that each time the two color difference signals of a line detected on the transmission must again be repeated on the reception side. This means that each of the two color difference signals is used successively twice to create simultaneous color type signals. Due to the odd number of lines of the detection frame and the distribution by half of the number of lines for the two chrominance signals, it is obtained that for a color jump in the vertical direction, after ie decoding, the geometric location of the color transition of successive images no longer coincides. The result, depending on the type of color transition, is a phenomenon of low color flickering.

  frequency, which is annoying. In the case of natural images

  Real, there are characteristic agitation effects for the sequential type of cculator transmission processes, effects which do not exist in the case of

  simultaneous color transmission processes.

  The present invention thus aims to create a process of the above type considerably reducing the effects of flicker at low frequency so that these effects are

  practically imperceptible to reproduction.

  To this end, the invention relates to a method of the above type, characterized in that the color difference signals created by the decoding (if necessary after an analog / digital conversion) are subjected to a controlled recursive filtering, then , if necessary after A / D conversion, on other stages

following for further treatment.

  The process according to the invention offers the advantage of

  ge to remove to a very large extent the effects

  parasites mentioned above and result in a qua-

  significantly improved image clarity compared to

  that obtained by conventional decoders.

  According to another characteristic, the control of the recursive filtering is done using a

movement detector.

  According to another characteristic, the control of the recursive filtering is done using a

vertical stop detector.

  According to another characteristic, the color difference signals, after the controlled recursive filtering as well as the corresponding luminance signal are supplied to the stages provided for the

  reproduction on the image screen of a cathode ray tube.

  According to another characteristic, the color difference signals, after controlled recursive filtering as well as the corresponding luminance signal are applied to the stages provided for a

new coding.

  The invention also relates to a circuit for implementing the above method, this circuit being characterized in that the outputs of the decoder are connected for the color difference signals at the input of each time an analog / digital converter. the outputs of which are connected by a multiplexer to a digital noise reduction system comprising a controlled recursive filter and in that the output of the recursive filter is applied

  by a digital / analog converter to the demulti-

  plexer for the other processing stages.

  An exemplary embodiment of the invention is shown in the drawing and will be described in more detail

detailed below.

  The figure mainly shows the process-

  of the FBAS I color video signal applied to the terminal

  ne 1 corresponding for example to the SECAM standard and giving the two color difference signals RY and BY directly by decoding using the decoder 2. The two color difference signals are first applied to a stage 3 formed each time an analog-digital A / D converter for each color difference signal and a multiplexer to be digitized, then multiplied over time; thus the entry of a recursive filter 4

  receives 8-bit digital signals.

  The recursive filter 4 is composed in a known manner of a first multiplier 6, the first input of which receives these color difference, multiplexed, digital signals and the other input of which receives a signal of attenuation coefficient (1-k). The output of the first multiplier 6 is connected to the first input of an adder 7, the second 1o input of which receives the output signal of a second multiplier 9. In this second multiplier 9, the delayed color difference signal is multiplied in a delay circuit 11 in the form of digital image memory and of another attenuation coefficient k applied to the second input of the multiplier 9. This recursive filter 4 known per se averages and thus reduces the signal amplitudes not repetitive from one image to another. The coefficients (1-k) and k determine this average. These coefficients are thus either created by a circuit 12 for the detection of movement, or by a circuit 13 for the detection of vertical edges. The two circuits 12 and 13 have been known for a long time and need not be described in more detail

in the present context.

  The output of the recursive filter 4 is applied to a stage 14 composed of an A / D converter and a demultiplexer. The digital color difference signals are thus transformed into analog signals and two simultaneous R-Y and B-Y signals are formed which are supplied to outputs 16 and 17 for further processing in the video image reproducing apparatus. Another possibility for further processing of these output signals consists in supplying the color difference signals as well as the luminance signal (available at terminal 18) to an encoder 19 to carry out a new encoding and to give a second color video signal FBAS II for example according to the PAL standard.

Claims (4)

  1 ') Method for reducing color flicker when reproducing color video signals for color difference signals transmitted sequentially online, method characterized in that the color difference signals created by decoding (if applicable) after analog / digital conversion) are subject to controlled recursive filtering (in 4), then, if necessary after A / D conversion to other stages following for further treatment.   2 ') Method according to claim 1, characterized in that the control of the recursive filtering (in 4) is done using a motion detector (12).   3 :) Method according to claim 1, characterized in that the control of the recursive filtering (in 4) is done using a stop detector vertical (13).   4 ') Method according to claim 1, characterized in that the color difference signals, after the controlled recursive filtering (in 4) as well as the corresponding luminance signal are supplied to the stages provided for reproduction on   the picture screen of a cathode ray tube.   ') Method according to claim 1, characterized in that the color difference signals, after controlled recursive filtering (in 4) as well as the corresponding luminance signal are applied to the stages (19) provided for a new coding. 6 ') Circuit for the implementation of   method according to any one of claims 1 to   3, with a decoder (2) for decoding the color video signal (FBAS I) with color difference signals transmitted sequentially online, circuit characterized in that the outputs of the decoder (2) are connected for the signals difference in color at the input each time an analog / digital converter (3) whose outputs are connected by a multiplexer to a noise reduction system   (4, 12, 13) digital with a recursive filter.   (4) controlled and in that the output of the recursive filter   is applied by a digital / analog converter   logic (14) to the demultiplexer for the other stages treatment.