WO1998028918A1 - Pal demodulation - Google Patents
Pal demodulation Download PDFInfo
- Publication number
- WO1998028918A1 WO1998028918A1 PCT/IB1997/001333 IB9701333W WO9828918A1 WO 1998028918 A1 WO1998028918 A1 WO 1998028918A1 IB 9701333 W IB9701333 W IB 9701333W WO 9828918 A1 WO9828918 A1 WO 9828918A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- pal
- color
- difference signals
- signal
- demodulated
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N11/00—Colour television systems
- H04N11/06—Transmission systems characterised by the manner in which the individual colour picture signal components are combined
- H04N11/12—Transmission systems characterised by the manner in which the individual colour picture signal components are combined using simultaneous signals only
- H04N11/14—Transmission systems characterised by the manner in which the individual colour picture signal components are combined using simultaneous signals only in which one signal, modulated in phase and amplitude, conveys colour information and a second signal conveys brightness information, e.g. NTSC-system
- H04N11/16—Transmission systems characterised by the manner in which the individual colour picture signal components are combined using simultaneous signals only in which one signal, modulated in phase and amplitude, conveys colour information and a second signal conveys brightness information, e.g. NTSC-system the chrominance signal alternating in phase, e.g. PAL-system
- H04N11/165—Decoding means therefor
Definitions
- the invention relates to a method and device for demodulation of PAL television signals, and to a PAL television receiver comprising such a PAL demodulation device.
- PAL Simple In the first TV-sets with PAL color decoders, called PAL Simple, the designers of TV-sets used characteristics of the human eye-sight for additively color merging two successive video lines on the TV-screen. These lines slightly differed in hue, due to transmission phase-errors in the color carrier, but because of the PAL-system the correct color could still be seen, when the eyes were not too close to the TV-screen.
- the visual effect, of line alternating differences in color on the screen was called "Venetian blinds", also known as H/2-effect, because the alternating rate was half the line-frequency H.
- PAL-S Venetian blinds of PAL Simple
- PAL-D PAL Delay-line
- EP-A-0,675,658 discloses an adaptive type color demodulation apparatus for PAL system, which includes a first demodulation circuit (PAL-D) for demodulating a PAL system chrominance signal between scanning lines, a second demodulation circuit
- PAL-D first demodulation circuit
- PAL-S for demodulating the PAL system chrominance signal on a scanning line
- a vertical correlation detection circuit for detecting a vertical correlation between chrominance signals which are apart by two horizontal periods
- a selector for selecting either an output of the first demodulation circuit (PAL-D) or an output of the second demodulation circuit (PAL-S) according to the detected result of the correlation detection circuit.
- Hue distortion of the chrominance signal which occurs during signal transmission is cancelled even if the phase distortion is large and a precise color signal is demodulated even if there is no correlation between adjacent scanning lines.
- DE-A-39.31.903 shows a similar system also having two separate PAL chrominance demodulators.
- a first aspect of the invention provides a PAL chrominance demodulation method as defined in claim 1.
- a second aspect of the invention provides a PAL chrominance demodulation device as defined in claim 3.
- a third aspect of the invention provides a PAL television receiver as defined in claim 4.
- An advantageous embodiment is defined in the dependent claim 2.
- PAL-S demodulated color-difference signals are averaged to obtain PAL-D demodulated color-difference signals
- the PAL-S demodulated color-difference signals are applied to a vertical color transient detection obtain a control signal
- PAL demodulated color-difference signals are generated in response to the PAL-S demodulated color-difference signals and the PAL-D demodulated color-difference signals and in dependence upon the control signal.
- a PAL-S demodulation is a PAL demodulation without an averaging over a line period.
- the invention advantageously only has a single demodulation instead of the two separate demodulations for simple PAL (PAL-S) and delay-line PAL (PAL-D) present in the prior art.
- a color transient detector performs a median filter operation on three successive PAL-S demodulated (R-Y) / (B-Y) color difference lines.
- the detection is made on the basis of the modulated chrominance signal, so that vertical color details not thicker than a single line cannot be detected, whilst color changes without saturation changes remain unnoticed.
- color transients are detected on the PAL-S demodulated color-difference signals, so that even those tiny details and color changes without saturation changes are correctly detected.
- the luminance signal is employed to increase the detection resolution, but this has the disadvantage that luminance changes affect the way in which the chrominance signal is demodulated.
- a high resolution color transient detection is possible without artifacts.
- Temporary switching to PAL-S on detection of a color transient restores the loss on vertical color definition caused by the averaging operation of PAL-D.
- the use of a median filter makes the detector immune for H/2 effects, avoiding false detection on Venetian blinds.
- PAL-D operation stays effective for color areas without color transients, while the Venetian blinds artifacts of PAL-S are covered up by the color transient itself.
- Fig. 1 shows a PAL-S demodulation circuit as known from EP-A-0,675,658;
- Fig. 2 shows a vertical color transient adaptive circuit which, together with the PAL-S demodulation circuit of Fig. 1, forms an embodiment of a demodulation circuit in accordance with the present invention
- Fig. 3 illustrates an alternative element for part of Fig. 2;
- Fig. 4 shows an output part of a PAL television receiver in accordance with the present invention.
- Fig. 1 shows a PAL-S demodulation circuit 301 as known from Fig. 2 of EP-A-0,675,658, incorporated herein by reference for further details.
- a PAL CVBS input signal is applied to a Y/C separator which furnishes a luminance signal Y and a chrominance signal C.
- a subcarrier generator 302 furnishes a color subcarrier frequency signal fsc to a 90° phase shift circuit 303, and to a 0° and 180° line switching circuit 304 which also receives a line alternating signal H'.
- the chrominance signal C is applied to a B-Y demodulator 305, which also receives an output signal of the 90° phase shift circuit 303, to furnish a PAL-S demodulated blue color-difference signal (B-Y) 2 .
- the chrominance signal C is applied to a R-Y demodulator 306, which also receives an output signal of the 0° and 180° line switching circuit 304, to furnish a PAL-S demodulated red color-difference signal (R-Y) 2 .
- the PAL-S demodulated red and blue color-difference signals from the PAL-S demodulator of Fig. 1 are each applied to a vertical color transient adaptive circuit as shown in Fig. 2.
- the input color-difference signal is applied to PAL-S input S of a fader 206 thru a compensating delay 200.
- the input color-difference signal is also applied to a cascade connection of two line (IH) delay circuits 201, 202.
- the input signal and the output signal of the line delay circuit 201 are averaged by an adder 203 and a halving circuit 204, and the average (a PAL-D demodulated color-difference signal (R-Y) j or (B-Y) 1 ; respectively) is applied to a PAL-D input D of the fader 206 thru a compensating delay 205.
- the non-delayed (OH) input color-difference signal, the once delayed (IH) color-difference signal at the output of the line delay 201, and the twice delayed (2H) color-difference signal at the output of the line delay 202, are applied to a median filter 213 for furnishing a median signal M.
- a comparator 214 compares the median signal M to the non-delayed signal OH.
- the comparison result diff is squared by means of a multiplier 215 to form a control signal CTRL for the fader 206.
- the control signal CTRL is indicative of the magnitude of the output signal diff of the comparator 214.
- an absolute value circuit can be used instead of the squaring circuit 215.
- the control signal CTRL is applied to a limiter 211 to obtain a fading coefficient k.
- the fading coefficient k is applied to a - input of a subtracter 212, the + input of which receives a 1, to furnish a complementary fading signal 1-k.
- the PAL-S demodulated input signal of the fader 206 is applied to a multiplier 207 for multiplication by the fading coefficient k.
- the PAL-D demodulated input signal of the fader 206 is applied to a multiplier 208 for multiplication by the complementary fading coefficient 1-k.
- Output signals of the multipliers 207, 208 are averaged by an adder 209 and a halving circuit 210 to obtain an output color difference signals (R-Y) 0 or (B-Y) 0 .
- Fig. 3 shows an alternative 106 for the fader 206 in which a hard switch is effected between the PAL-S demodulated signal and the PAL-D demodulated signal.
- the median filter 213 gets the 0H-, IH- and 2H- delayed signal on its inputs, where H stands for the period time of the received (R-Y) or (B- Y) color difference signal. On its output the median-value M can be found.
- S is the PAL- Simple signal and except for some propagation time compensation by delay circuit 200, S is equal to OH.
- D is the PAL Delay signal. D is the average of OH and IH and is time compensated by delay 205. In the switch option of Fig. 3, the output signal is equal to S or D. In the fader option of Fig. 2, the output signal is a mixture of S and D. The time compensation delays the signals S and D to the correct moment of decision by the switch 106 or the fader 206.
- Example 4 When we have a vertical change in color and we have H/2, then: OH is not equal to 2H which is not equal to IH. In this case, the signal that has the median value is passed over to M and it depends on the degree of difference between M and OH, if the switch switches to S or not.
- Fig. 4 shows an output part of a television receiver in accordance with the present invention.
- a matrix circuit Mx receives the luminance signal Y from the Y/C separation circuit 300 of Fig. 1 , and output color difference signals (R-Y) 0 and (B-Y) 0 from circuits as shown in Fig. 2, to generate RGB color signals for a display D.
- the vertical color transient restorer circuit in accordance with the present invention restores the vertical color definition, by using PAL-S on vertical color transients and PAL-D in color areas, thereby avoiding Venetian blinds in color areas, where they are most visible.
- a color transient detector performs a median filter operation on three successive color lines (R-Y)n (OH), (R-Y)n-f- l (IH) and (R-Y)n+2 (2H). On a transient event, the median of (R-Y)n, (R-Y)n + 1 , and (R-Y)n+2 is not equal to (R-Y)n. Switching to PAL-S on that event, restores the vertical color definition.
- a median filter is not compulsory; one can also compare (R-Y)n (OH) to (R-Y)n + 1 (IH) and perform the switching to PAL-S accordingly, but that makes the circuit vulnerable to H/2. At a certain amount of H/2 the Venetian blinds will be detected as vertical color transients and that will switch the circuit to the PAL-S mode in a H/2-signal-condition, where we need PAL-D very most.
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- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Processing Of Color Television Signals (AREA)
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP10528569A JP2000505981A (en) | 1996-12-23 | 1997-10-23 | Demodulation of PAL signal |
EP97944057A EP0888692A1 (en) | 1996-12-23 | 1997-10-23 | Pal demodulation |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP96203696 | 1996-12-23 | ||
EP96203696.8 | 1996-12-23 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1998028918A1 true WO1998028918A1 (en) | 1998-07-02 |
Family
ID=8224758
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/IB1997/001333 WO1998028918A1 (en) | 1996-12-23 | 1997-10-23 | Pal demodulation |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0888692A1 (en) |
JP (1) | JP2000505981A (en) |
CN (1) | CN1216200A (en) |
WO (1) | WO1998028918A1 (en) |
Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2169772A (en) * | 1985-01-11 | 1986-07-16 | Quantel Ltd | Detecting horizontal colour changes in a video signal |
GB2239371A (en) * | 1989-09-25 | 1991-06-26 | Broadcast Television Syst | PAL signal chrominance decoder |
EP0565333A2 (en) * | 1992-04-06 | 1993-10-13 | Questech Limited | Apparatus for processing a pal colour television signal |
EP0645936A2 (en) * | 1993-09-24 | 1995-03-29 | Snell & Wilcox Limited | Video signal processing |
EP0675658A2 (en) * | 1994-03-31 | 1995-10-04 | Matsushita Electric Industrial Co., Ltd. | Adaptive type color demodulation apparatus for pal system |
EP0735783A2 (en) * | 1995-03-27 | 1996-10-02 | Matsushita Electric Industrial Co., Ltd. | A PAL-system adaptive color-signal demodulator |
-
1997
- 1997-10-23 WO PCT/IB1997/001333 patent/WO1998028918A1/en not_active Application Discontinuation
- 1997-10-23 CN CN 97193799 patent/CN1216200A/en active Pending
- 1997-10-23 JP JP10528569A patent/JP2000505981A/en active Pending
- 1997-10-23 EP EP97944057A patent/EP0888692A1/en not_active Withdrawn
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2169772A (en) * | 1985-01-11 | 1986-07-16 | Quantel Ltd | Detecting horizontal colour changes in a video signal |
GB2239371A (en) * | 1989-09-25 | 1991-06-26 | Broadcast Television Syst | PAL signal chrominance decoder |
EP0565333A2 (en) * | 1992-04-06 | 1993-10-13 | Questech Limited | Apparatus for processing a pal colour television signal |
EP0645936A2 (en) * | 1993-09-24 | 1995-03-29 | Snell & Wilcox Limited | Video signal processing |
EP0675658A2 (en) * | 1994-03-31 | 1995-10-04 | Matsushita Electric Industrial Co., Ltd. | Adaptive type color demodulation apparatus for pal system |
EP0735783A2 (en) * | 1995-03-27 | 1996-10-02 | Matsushita Electric Industrial Co., Ltd. | A PAL-system adaptive color-signal demodulator |
Also Published As
Publication number | Publication date |
---|---|
CN1216200A (en) | 1999-05-05 |
EP0888692A1 (en) | 1999-01-07 |
JP2000505981A (en) | 2000-05-16 |
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