DE3643424C1 - Method for decoding PAL colour television signals, in which the digitised PAL signal is separated into its luminous and chrominous components by digital filtering - Google Patents

Abstract

To decode PAL colour television signals, the digitised PAL signal is separated into its luminous and chrominous components by digital filtering, in which the filter characteristics is matched to the temporal spectral structure of the components (Y, U, V). Due to the fact that the PAL signal is sampled in the time domain, the filter variation is periodically repeated in the base band. The centre frequencies of the periodically repeated filter variations are corrected in dependence on the spectral component caused by movement in the picture content in the temporal spectrum of the PAL signal.

Description

The invention relates to a method according to the Preamble of claim 1. Such a Ver driving is from "television and cinema technology", 37th year, No. 12, 1983, pp. 511 to 519.

It is for decoding a PAL color television signal known ("television and cinema technology", 37th year, No. 12, 1983, pp. 511 to 519) to digitize the PAL signal, e.g. with a sampling frequency of 13.5 MHz accordingly the CCIR studio standard, and the digitized PAL Signal of a temporal (pictorial) or vertical to undergo (line by line) comb filtering. In the Temporal comb filtering can only be done for standing Images, regardless of what image content, an exact Separation of the luminance and chrominance components pass. Because movements in the image content become too high Crosstalk of the luminance components into the chrominance components and vice versa, takes place in the known Procedure depending on a simple movement detection of a changeover from temporal comb filtering on vertical comb filtering. With the vertical comb fil However, an error-free separation can only be achieved of the luminance and chrominance components if There are exactly vertical structures in the image content. For all other image content, a Shift the vertical spectral components one more or  less large crosstalk also due to the switchover the filter characteristics do not prevent.

The object of the invention is in a procedure ren of the type mentioned the quality of the PAL signal improve decoding.

According to the invention, this object is characterized by the solved the features of claim 1.

An advantageous development of the Ver driving arises from the subclaim.

The invention is based on consideration, by adaptation the digital filter characteristic to the detected Be optimal filtering of the luminance and to achieve chrominance components, making one against side crosstalk of these components largely ver is avoided.

The invention is explained in more detail with reference to the drawings. It shows:

Figure 1 shows the temporal spectrum of a PAL color television signal with stationary image content.

Fig. 2 shows the temporal spectrum of a PAL color television signal with movement in the image content, and

Fig. 3 is a block diagram of a PAL decoder with motion-adaptively controlled filter for performing the method according to the invention.

In Fig. 1 the temporal spectrum of a PAL color television signal is shown with stationary image content. Here, the spectral luminance components Y occur at multiples of the frame rate. Offset with an offset of a quarter of the frame rate to the luminance components, the spectral components U and V for the chrominance component come to rest. With the help of full-frame memories, used in a known comb filter decoder for digitized PAL signals, the luminance and chrominance components for stationary image content can be separated without errors. The filter curve for filtering out the chrominance component is shown in dashed lines in FIG. 1.

If there is movement in the image content, the spectral components shift. Such a shift of the spectrum is shown in Fig. 2 for the chrominance components U and V. With the known filter mentioned above, the components for luminance and chrominance can no longer be separated correctly. Luminance components occur in the chrominance channel and vice versa. This creates the known interference effects, such as cross-color and cross-luminance.

Will a tax instead of the fixed full screen filter bares filter that uses the deviating spectral share (caused by movement) is tracked, so the spectrum of the PAL signal can be error-free again be disassembled.  

Such a controllable filter in a possible simple embodiment for separating the chromi nance components is shown in FIG. 3. Here, the digitized PAL signal is read into n image memories 10 in order to determine the moving image parts on the one hand and by means of a motion detector switched in parallel with the n image memories 10 20 determine their speed according to size and direction. This information obtained during the motion vector determination is converted into control information which is fed to buffer memories 30 , 40 , of which buffer memory 30 is connected to the input of n image memories 10 and buffer memory 40 to the output of n image memories 10 . The filter characteristics can be changed by the buffer memory 30 , 40 and adapted to the movement occurring in the image. By simply subtracting the output signals of the buffer memories 30 , 40 by means of a subtractor 50 , the chrominance component can then be obtained.

With the motion-adaptive filter shown in FIG. 3, the luminance and chrominance components from the PAL spectrum can largely trouble-free, even for moving image content to be recovered.

Claims (3)

1. A method for decoding PAL color television signals, in which the digitized PAL signal is broken down by digital filtering into its luminance and chrominance components, the filter characteristic being adapted to the temporal, spectral structure of the components, characterized in that as a result the temporal sampling of the PAL signal, the filter curve is repeated periodically in the baseband, and that the center frequencies of the periodically repeated filter curves are tracked as a function of the spectral components caused by movement in the image content in the tempo ral spectrum of the PAL signal, the movement in the Image content is determined by amount and direction. 2. The method according to claim 1, characterized in that that the pass band of each filter curve in the tempora len spectrum a selectable multiple of the full screen alternating frequency is, preferably half the full frame rate corresponds.   3. The method according to claim 1 or 2, characterized draws that the pass band of each filter curve a selectable multiple in the temporal spectrum the frame rate is preferably corresponds to half the frame change frequency.