Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1991-03-25
1992-11-24
Britton, Howard W.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
H04N 701
Patent
active
051667924
DESCRIPTION:
BRIEF SUMMARY
This invention relates to video stores and to methods of digital standards conversion and other video signal processing techniques utilising such stores.
In Europe, the main scanning standard for broadcast television signals uses 625 lines per picture and 50 fields per second. North America and Japan, however, use 525 lines per picture and approximately 60 fields per second. It can therefore be appreciated that a conversion process is necessary before programmes originating on one standard can be broadcast in countries using another standard. Whilst conversion could be achieved optically, digital electronic conversion techniques offer far better performance.
It will be understood that the digital conversion process requires lines in the output standard to be constructed by an interpolation procedure over a number of adjacent lines in the input standard. A similar interpolation procedure is required to construct fields.
In one approach adopted hitherto for electronics standards conversion, (see for example GB-A-1599346) line interpolation is conducted in an input stage with information from, say, three adjacent lines being utilised to construct a line at the position required for the output standard. The line information is loaded into a field store which is capable of asynchronous operation. Picture information may accordingly be read out of the video store at the field rate corresponding to the output standard. According to a suitable field interpolation algorithm, picture information in the video store is updated to a value which reflects both the current and preceding field values.
Because the video store is asynchronous, complicated control circuitry must be employed to regulate read and write operations. It has, moreover, been found that this manner of conversion, where line interpolation and field interpolation are carried out sequentially, is not the optimum, and significant picture artefacts can arise.
An alternative approach, as shown in EP-A 003 182, utilises a plurality of input field stores which are each divided into separately readable line blocks. Fields of the incoming video signal are loaded successively into the field stores with the lines of each field being loaded successively into the separate blocks of that field store. In this way, information from m fields (typically two) and n lines (typically four) can be made available simultaneously for a combined line and field interpolation process in the output stage. This is regarded theoretically as superior to sequential line and field interpolation. The memory structure required for this approach is, however, inconvenient and difficult to implement on high density storage devices. There is the further difficulty that since all interpolation is conducted in the output stage, it is not possible to perform those processing steps (such as VTR drop-out correction) which require information from separate lines in the input stage.
Appropriate arrangements of field stores can be used in video signal processing techniques other than standards conversion, examples of such further techniques being synchronization, noise reduction and --particularly in relation to video recorders --slow and fast motion. Reference is directed to GB 2 098 021A which discloses digital television apparatus having three field stores with reading and writing operations being rotated cyclically about the stores. Depending upon the rate of supply of a video signal to the field store arrangement, a choice is made whether to write information to one or two of the field stores and, similarly, whether to read from one or from two of the field stores. The content of any field store always corresponds with a single field of the input video signal except in the trivial case where the data associated with a particular pixel is detected as corrupt and the data associated with the same pixel in the preceding frame left undisturbed.
The described field store arrangement offers some advantages in accomodating slow and fast motion signals from a digital video tape recorder but is not sui
REFERENCES:
patent: 4276565 (1981-06-01), Dalton
patent: 4335395 (1982-06-01), Clarke
patent: 4558377 (1985-12-01), Collins
patent: 4698698 (1987-10-01), Collins
Britton Howard W.
Snell & Wilcox Limited
LandOfFree
Video signal processing and video stores does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Video signal processing and video stores, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Video signal processing and video stores will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-926114