Facsimile and static presentation processing – Static presentation processing – Attribute control
Patent
1985-02-27
1987-09-29
Jillions, John M.
Facsimile and static presentation processing
Static presentation processing
Attribute control
358 40, H04N 1108
Patent
active
046972064
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the transmission and reception of color television signals in component form and more particularly to a method an apparatus for handling the chrominance components of the signals.
The present invention will be described in relation to a component television signal known as a Multiplexed Analogue Component (M.A.C.) signal although this is but one application of the present invention.
SUMMARY OF THE INVENTION
The present invention provides a method of assembling chrominance components signals comprising providing a plurality of fields of video signals in which the two different types of chrominance component signals alternate within each field, and arranging the fields so as to produce a resultant chrominance structure which is noninterlaced and contains alternate chrominance component signals both within each field and between adjacent fields, whereby to permit enhanced vertical chrominance resolution.
Features and advantages of the present invention will be apparent from the following description of an embodiment thereof when taken in conjunction with the accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows diagrammatically the line structure for the chrominance components of a MAC-type signal;
FIG. 2 shows a graph representing the repeat spectra in vertical and temporal frequency produced by the line structure of FIG. 1;
FIG. 3 shows diagrammatically the proposed type of line structure;
FIG. 4 shows a graph representing the repeat spectra in vertical and temporal frequency produced by the line structure of FIG. 3;
FIG. 5 shows a diagrammatic representation of a filter producing the line structure shown in FIG. 3; and
FIG. 6 shows the characteristic of the filter shown in FIG. 5.
DETAILED DESCRIPTION
MAC is defined to code the two color difference components (U and V in Europe) on alternate lines with a frame-reset sequence. This sequence is illustrated in FIG. 1.
There are sound reasons why this sequence has been selected in place of the alternative four-field sequence which is not reset each frame. The main reason is the residual alias components in the frame-reset case are much less disturbing. In addition, if such a signal were ever to be processed in the studio then its two-field sequence would be easier to handle than a four-field sequence. An implication of using this sequence however is that the vertical chrominance resolution is limited to a quarter of the luminance vertical resolution capability. This is because effectively there are only 144 (575/4) vertical samples of each colour in an active picture scan whereas there are 575 active vertical samples of luminance. In order to achieve the full vertical resolution afforded by the 575 lines, field stores are required in the receiver. Nevertheless even if this complexity is allowed for color the vertical chrominance resolution is still limited to that offered by 144 lines.
In frequency terms this limitation is evident by considering the repeat spectra (in vertical and temporal frequency) generated by this alternate line sequence, as illustrated in FIG. 2.
The open circles are those repeats arising from the 625 interlace scan. The extra repeats introduced by alternate line omission in a frame reset fashion are illustrated by the shaded circles. These repeat spectra are half-amplitude but nevertheless they impose a Nyquist-limiting vertical chrominance frequency of 72 cycles per picture height (equivalent to 1.8 MHz horizontally). In practice the chrominance vertical resolution obtained after pre- and post- filtering is equivalent to 1.1 MHz horizontally (-3 dB).
If we wish to maintain a frame-reset sequence for transmission, techniques for achieving a vertical chrominance resolution greater than the Nyquist limit described above are not obvious. Nevertheless the following line of thought gives a clue to a possibility: with the current approach there appears to be a paradox. Although there are half as many lines of each colour d
REFERENCES:
patent: 2273172 (1942-02-01), Beers
patent: 4210927 (1980-07-01), Yumde et al.
patent: 4516151 (1985-05-01), Stahler
IBA Publication, "Line Sequential Colour Transmission and Vertical Filtering in MAC", G. Tonge et al, Dec. 1983.
"An Extensible Family of Standards"; E. J. Wilson & G. Tonge; pp. 13 and 14; Mar. 1982: IBA Technical Review No. 16.
Independent Broadcasting Authority
Jillions John M.
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