Rec. ITU-R BT.1197-1
RECOMMENDATION ITU-R BT.1197-1*
Enhanced wide-screen PAL TV transmission system
(the PALplus system)
(Question ITU-R 10/6)
The ITU Radiocommunication Assembly,
a) that the 16:9 aspect ratio provides an enhanced viewing experience, particularly on large screen receivers, and is likely to be adopted for new digital services;
b) that there are indications that the public interest in the new 16:9 aspect ratio is growing;
c) that PAL services are likely to continue for several decades, whatever new services are introduced;
d) that evaluations, summarized in Appendix 1 to Annex 1, have shown that the PALplus system can provide high quality 16:9 pictures for wide-screen receivers whilst maintaining compatibility with existing 4:3 receivers (using 16:9 letterbox);
e) that the signalling system required by PALplus for receiver control has been recommended in Recommendation ITU-R BT.1119;
f) that Recommendation ITU-R BT.1118 recommends that when enhancements to existing television systems are made, some or all of the modular enhancements and features listed in Annex 1 to that Recommendation should be used;
g) further that two of these modules are:
– coder requirements for accommodating wide aspect ratio signals, and
– coder requirements for reducing cross-effects and optimal use of the signal spectrum;
h) that the PALplus system can provide for the two modules listed in § h) above;
j) that although the PALplus system does not permit open subtitling in the black band below the letterbox PALplus signal, this can be mitigated by use of the MACP picture enhancement technique of PALplus which allows open subtitling to be included anywhere within the transmitted image,
1 that where administrations or broadcasters wish to enhance the delivery of conventional definition PAL (see Note 1) television with:
– compatible 16:9 wide-screen,
– compatible encoding to reduce cross-effects
and make optimum use of the video signal spectrum, the PALplus system, as specified in Annex 1, should be used.
NOTE 1 – In the case of PAL systems B, G, H, I, D and K;
2 that where one of these two enhancement modules is required individually for the enhancement of the delivery of conventional PAL (see Note 1) television, the relevant module of the PALplus system (see Note 2), as specified in Annex 1, should be used.
NOTE 1 – In the case of PAL systems B, G, H, I, D and K.
NOTE 2 – The term “PALplus” identifies a system for transmissions in which all modules of the system described in Annex 1 are used (see also Table 1).
PALplus system specification
TABLE OF CONTENTS
1 Introduction 3
2 Essential features of a PALplus transmission 4
2.1 The PALplus signal 6
2.1.1 Input picture signal to the PALplus encoder 6
2.1.2 The encoded composite PALplus signal 6
3 The PALplus encoding processes 7
3.1 Vertical conversion 7
3.1.1 Encoder vertical conversion of luminance 8
3.1.2 Encoder vertical conversion of chrominance 8
3.2 Vertical helper encoding 12
3.3 Motion adaptive colour plus 13
3.3.1 Pre-processing in the encoder 14
3.3.2 Motion detector operation 17
3.4 Reference signals 19
3.5 Signalling 19
3.5.1 Signalling examples 20
APPENDIX 1 – Report on the European Broadcasting Union (EBU) evaluation of the PALplus system 26
APPENDIX 2 – Informative note on receivers for the PALplus system 38
APPENDIX 3 – Filter name abbreviations 39
APPENDIX 4 – Studio production guidelines for transmissions to be encoded into PALplus and guidelines for handling PALplus encoded signals 40
PALplus is an enhanced transmission system which has been designed to allow existing PAL broadcasters to offer wide screen pictures with greatly reduced levels of conventional PAL artefacts, whilst retaining a high level of compatibility with the PAL transmission infrastructure and with existing PAL receivers.
The format of the primary encoder input and decoder output signals for PALplus is 625/50/2:1, with an aspect ratio of 16:9. A 1250/50/2:1 HDTV source may be used after downconversion to 625/50/2:1.
The wide-screen picture is transmitted in letterbox format to achieve compatibility with existing 4:3 receivers. Loss of vertical resolution (as compared to the 576 active line source picture) is minimized in the PALplus receiver by making use of a vertical helper signal transmitted in the black bands above and below the letterbox picture.
The PALplus system has two modes of operation. These are called “film mode”, which is used only with film sources, and “camera mode” which is used with normal 50 Hz video sources. Both the vertical conversion (to the letterbox picture) and the motion adaptive colour plus (MACP) method of improved chrominance/luminance separation make use of a camera mode and a film mode to give optimum system performance.
Starting from a 625/50/2:1 4:2:2 digital component input signal (in accordance with Recommendation ITU-R BT.601, based on 13.5 MHz sampling (see Note 1)) with 576 active lines per frame and an aspect ratio of 16:9, a conversion to 430 active picture lines is first carried out. When the source provides 50 Hz motion (camera mode), this conversion must be performed intra field in order to avoid motion artefacts but, when the source is known to have only 25 Hz motion (i.e., in film mode), then an intra frame conversion (using samples taken from the two fields of a frame) is used. The letterbox picture signal used for transmission has only three quarters of the number of active picture lines as the source; in order to minimize loss of vertical resolution in the PALplus display, the black bands are used to transmit a vertical helper signal.
An enhanced PAL encoding and decoding technique known as “motion adaptive colour plus” is used to reduce PAL luminance/chrominance crosstalk artefacts and to maximize horizontal resolution. In film mode, the system takes advantage of the known temporal redundancy of the signal and uses an intra frame PAL encoding technique (fixed colour plus). In camera mode, the same technique is applied to appropriate areas of each picture frame. However, in areas containing moving saturated colour (usually representing only small parts of typical pictures), there is likely to be a significant amount of movement between the adjacent fields of a source picture frame, which could lead to occasionally visible colour judder if colour plus processing were applied. To minimize this problem, in such areas of the picture, the system reverts adaptively to a simpler form of PAL encoding, making use of motion detectors in both the encoder and decoder to identify areas of fast colour motion between adjacent frames.
Ghost cancellation is an optional enhancement. The parameters of the ghost cancellation reference signal are given in Recommendation ITU-R BT.1124, Annex 1, § 1.3.
NOTE 1 – All references to Recommendation ITU-R BT.601 in this Recommendation refer to the 13.5 MHz sampling variant specified in Part A.