A METHOD AND A DEVICE FOR ENCODING AND DECODING OF INTERLACED VIDEO SIGNALS BY A CODEC FOR PROGRESSIVE VIDEO SIGNALS

Abstract: A method of coding an interlaced video signal made up of fields combines at least two fields to form a frame using a transformation such that lines adjacent in a field are adjacent in the frame and codes on the basis of the frame.

Description: A Method and a Device for Encoding and Decoding of Interlaced Video Signals by a Codec for Progressive Video Signals The majority of the current video encoding and decoding systems working with conventional, interlaced broadcast video signals use codecs specifically designed for interlaced video signals, such as compression codecs using the so-called ISO MPEG2 ISO standard (which can also support progressive signals). In other situations where progressive video signals are processed, video codecs supporting progressive video format are deployed, and sometimes codecs that support only progressive, such as H.261 or H.263 (ITU) video signals are used. However, in some situations it is desirable to encode and decode interlaced video signals using a progressive only codec. For example, this situation may arise when only a progressive video codec is available and the video material is in the interlaced format. One possible solution is to perform a motion-compensated conversion from interlaced to progressive video on the input of the progressive codec before encoding. A reverse transformation, e.g. from progressive to interlaced is performed after the decoding in the decoder. However, interlaced-to-progressive and progressive-to-interlaced conversion is complex and requires expensive hardware or significant processing power if performed in software. Thus such approach is often not practicable or economical. It is known to interleave the lines of pairs of fields of an interlaced video signal and then to process the result as a single frame. However, it may not be practical or economical to perform such a conventional scan conversion. Furthermore, due to the time difference between successive fields of the interlaced video and object or camera motion, signal correlation between the neighbouring lines in the line-interleaved frame may be less then than the signal correlation between adjacent lines in the original fields. This can result in less effective coding. This invention proposes a novel, low-cost solution to encoding and decoding of an interlaced video signal using a progressive-only video codec and which retains good coding quality. An aspect of the inventive idea is to group pairs or even numbers of the consecutive interlaced fields and convert them into super-frames, using a geometric transformation. The geometric transformation T maps 2*k (k=l, 2, ...) video fields, each n*m pixels (e.g. n pixels horizontally by m pixels vertically) into one 2*k*n*m super-frame. Such super-frames are then encoded by the progressive encoder. In the progressive decoder, super-frames are decoded normally and then converted back into interlaced video fields via inverse transformation T " . Embodiments of the invention will be described with reference to the accompanying drawings, of which: Fig. 1 is a block diagram illustrating elements of a method according to an embodiment of the invention; Fig. 2 is a block diagram illustrating a method and apparatus according to an embodiment of the invention; and Fig. 3 is a block diagram illustrating elements of a method according to a second embodiment of the invention. With reference to Figs. 1 and 2, each pair of interlaced fields n and n+1 is combined by a mapper 2 to form a respective, progressive super-frame, using a transformation T. Each super-frame S is then coded using a progressive video encoder 4. Similarly, in decoding, the super-frame is decoded using a progressive decoder 6, then transformed back to interlaced fields n, n+1 using the inverse transformation T *1 by a mapper 8. In this embodiment, the transformation T maps the first of each pair of interlaced fields to the top half of the respective super-frame and the second field to the bottom half of the respective super-frame. As a result, there is a boundary half-way down the super-frame corresponding to the boundary between the two fields, but elsewhere the correlation between adjacent lines in the super-frame is as for adjacent lines in the original fields. In the above embodiment, fields n and n+1, are combined (and subsequently fields n+2 and n+3 and so on). In an alternative embodiment, shown in Fig. 3. each set of four consecutive fields, that is. fields n, n+1. n+2. n+3 are combined to form each super-frame. In this embodiment, fields are arranged adjacent to each other and one above another, as shown. In the above embodiments, the temporal resolution of the original sequence (interlaced) is reduced for coding by a factor of a power of two, but with the benefit of an increase of the spatial resolution by the same factor. This may be useful if the progressive codec has a higher spatial resolution compared with the input interlaced sequence. For example, if an original interlaced video signal has CIF spatial resolution and a temporal resolution of 30 Hz. and the progressive video codec only supports 15 Hz temporal resolution, but at 2xCIF spatial resolution, then this implementation can be effectively applied. In alternative embodiments, numbers of fields other than two or four can be combined to form the super-frames, and various transformations can be applied. The fields can be arranged in various ways in the super-frame such as horizontally or vertically or a combination of horizontally and vertically, depending, for example, on the resolution of the original images and of the codec. The fields can be divided into blocks with the blocks arranged and combined into a super-frame. Lines can be omitted from the fields in the super-frame if desired. The decoder is not necessarily a progressive-type decoder.

Claims: CLAIMS: 1. A method of coding an interlaced video signal representing image fields, the method comprising combining at least two fields to form a frame using a transformation such that lines adjacent in a field are adjacent in the frame and coding on the basis of the frame. 2. A method as claimed in claim 1 wherein even numbers of fields are combined to form a frame. 3. A method as claimed in claim 2 wherein two fields are combined to form a frame. 4. A method as claimed in claim 1 or claim 2 wherein more than two fields are combined to form a frame. 5. A method as claimed in any one of claims 1 to 4 wherein the coding is performed using a progressive-type coder. 6. A method as claimed in claim 5 wherein the spatial resolution of the progressive-type coder is at least n times the spatial resolution of the fields of the interlaced video signal, where n is the number of fields making up a frame. 7. A method of decoding an interlaced video signal coded according to the method of any one of claims 1 to 6 comprising decoding a coded frame using a decoder and then performing the inverse of said transformation to obtain an interlaced video signal. 8. A method as claimed in claim 7 wherein the decoder is a progressive-type decoder. 9. An apparatus for coding an interlaced video signal representing image fields comprising means for combining at least two fields to form a frame using a transformation such that lines adjacent in a field are adjacent in the frame and a progressive-type coder for coding the frame. 10. An apparatus for decoding an interlaced video signal coded using a method as claimed in any one of claims 1 to 6 or using an apparatus as claimed in claim 9 comprising a decoder and means for applying an inverse transformation to obtain an interlaced video signal. 11. An apparatus as claimed in claim 10 wherein the decoder is a progressive-type decoder. 12. A method of coding an interlaced video signal substantially as hereinbefore described as an embodiment with reference to the corresponding accompanying drawings. 13. A method of decoding a coded interlaced video signal substantially as hereinbefore described as an embodiment with reference to the corresponding accompanying drawings. 14. Apparatus for coding an interlaced video signal substantially as hereinbefore described as an embodiment with reference to the corresponding accompanying drawings. 15. Apparatus for decoding a coded interlaced video signal substantially as hereinbefore described as an embodiment with reference to the corresponding accompanying drawings.

Inventors: BOBER MIROSLAW, BOBER, MIROSLAW
Applicants: BOBER MIROSLAW, MITSUBISHI ELECTRIC INF TECH, BOBER, MIROSLAW, MITSUBISHI ELECTRIC INFORMATION TECHNOLOGY CENTRE
Application year: 2000
Main classification: H04N5
IPC codes: H04N5, H04N7