GB2044050A - Method of and Apparatus for Enhancing Television Pictures etc. - Google Patents

Abstract

A method of and apparatus for enhancing television pictures or VDU displays in which a key waveform is generated by logically combining (14) an input signal (12) with an attenuated (16) and an approximately one-line delayed (18) signal which is itself derived from the combined signal, and comparing (20) the combined signal with a reference (22) to provide the key output (24) when the combined signal exceeds the reference. Further outputs may be provided when the combined and reference signals are the same (26), or in dependence upon the relationship between the input and output of the delay (18). The various outputs, and the input can be logically combined to provide modified key waveforms. The outputs can be selected to provide desired caption inlays. <IMAGE>

Description

SPECIFICATION Method of and Apparatus for Enhancing Television Pictures Etc.

This invention relates to a method of an apparatus for enhancing television pictures or like displays produced by raster scanning. The invention is particularly applicable to the enhanced display of captions in broadcast television.

"Inlay" techniques, which are by now wellknown in television, involve the generation of a key waveform which is used to "cut a hole" in a background picture into which an infill scene or video signal is inserted. Captions can be inlaid in this manner by generating a key waveform from the caption itself. This can be essentially identical to the caption video envelope, or can be obtained by widening the caption video signal to give a larger horizontal shape using methods known in themselves, and then optionally displacing the caption to left or right relative to the key waveform. This gives a black edge around the characters of the caption, but only very limited effects can be obtained.

This invention provides a method of and apparatus for enhancing television pictures or like displays produced by raster scanning, in which an input signal representing the region of the display to be enhanced is logically combined with an attenuated and delayed signal, the resultant combined signal is delayed by approximately one line period and attenuated to provide the said attenuated and delayed signal, and the combined signal is compared with a reference to provide an output key signal in dependence upon the result of the comparison.

Preferably the delay period is adjustable. The amount of attenuation and/or the reference value are also preferably adjustable.

The invention enables the production of equipment which, while being essentially of relatively simple construction, nevertheless enables interesting displays to be produced.

While the invention will be described in relation to broadcast television, it is applicable in principle to otherVDU (visual display unit) displays such as produced by computer equipment.

The invention will be described in more detail, by way of example, with reference to the drawings, in which: Fig. 1 is a block circuit diagram of an analogue caption enhancer embodying the invention; Fig. 2 is a block circuit diagram of a corresponding digital device; Fig. 3 shows some of the enhanced displays which can be obtained; Fig. 4 is a waveform diagram illustrating how the circuit produces two of the enhanced displays of Fig. 3; and Fig. 5 shows additional logical elements used in producing some of the displays of Fig. 3.

Referring first to Fig. 1 , the caption enhancer 1G illustrated has an input 12 for receiving the output C of a caption generator (not shown) which may be of known type. The signal is received in normal television format. A nonadditive mixer (N.A.M.) 14 is connected to the input 12 and to the output of an attenuator 1 6 and performs the functions of an 'analogue OR gate', by selecting the higher of its two inputs as its output. A delay device 1 8 receives the output of the mixer 14 and provides a delay of approximately one line period; the exact amount is discussed below. The output of the delay device 18 is applied as the input to the attenuator 1 6.

This attenuator reduces the amplitude of the signal by a predetermined amount, expressed either as a proportion of the signal value, or alternatively as a fixed deduction which is applied until the data reaches zero. The delay 18 and attenuator 16 could if desired be connected in the other order.

The output of the mixer 14 is also applied as one input to a comparator or clipping circuit 20.

Here it is compared with a reference value N indicated diagrammatically at 22. The comparator output 24 constitutes the output of the device. In the present example the comparator output may simply take one of two values in dependence upon whether the mixer output is greater or less than the reference.

It is assumed that the caption signal has a positive value during the characters, and a zero value between characters. The signal is fed into the recirculating loop formed by the delay device 1 8 and attenuator 16. The gain around the loop is a little less than unity. Thus, assuming first that the delay device is of exactly one line period, the caption will be extended downwardly, but at steadily decreasing amplitude. This signal is compared in the comparator 20 with the reference 22. During the caption characters, and for a predetermined number of lines after them, the mixer output will be greater than the reference N and an output will be provided.

However, after a number of subsequent circulations determined by the degree of attenuation in the attenuator, on the one hand, and the relationship of the reference value to the input signal level, on the other, the mixer output will be less than the reference and the output will cease.

Thus it is seen that the caption has been extended downwardly.

Now it is assumed that the delay device has a delay of one picture element more than one line period (H+p). It will now be seen that the downward extension is shifted diagonally to the right on the picture, and the whole character will have the shape of a "shadow", as though lit from above and to the left. The angle of the diagonal depends upon the amount by which the delay period differs from one line period.

Fig. 2 shows a simple digital version 30 of the circuit. This in part corresponds to the analogue version of Fig. 1 and so it is convenient to use the same reference numerals for corresponding components. The number of bits used, n, determines the maximum lateral widening available. The OR gate 14 produces an output of which all the bits are at logical 1 when the caption is present, decaying to all zeros after 2" lines in the field below the caption. The comparison in comparator 20 is made with an adjustable number N to produce the output of desired depth.

In Fig. 2 the input caption C is shown as being in the form of the capital letter L. The key waveform K obtained at output 24 is also shown.

This key waveform can then be used to "cut a hole" in the primary video picture to allow infill of caption information. If as noted above the comparator 20 provides an output at 24 which takes one of two values depending on which input is the greater, then a switching waveform results which can be used to switch between two video signals. This is termed "hard lipping". However, this can produce undesired effects, e.g. caption noise, and it is therefore preferred to use "soft clipping" in which the comparator output changes gradually over a range. The resultant output is then applied to what is effectively a weighted adder circuit to change more gradually from one video signal to the other. This can be used, in dependence on the rate of change of the signal, to give pleasing soft edge effects.

The video signal used in the infill periods can be derived in a variety of ways. The original caption signal can be used to give a white character shape with a deep black drop shadow, giving a three-dimensional effect. Alternatively other waveforms can be used, e.g. colour waveforms or other video scenes. Further examples are given below.

In the Fig. 2 circuit, the comparator 20 is of a type providing an additional output 26 when the value of the recirculating data is equal to the reference N. This gives an outline waveform 0 as shown on Fig. 2. Also a second comparator 30 is included which compares the input and output of the delay 18 and provides an output when the input is greater than or equal to the output. The effect of this is to produce on output 32 a waveform S which is similar to the key waveform K but in which the extended bottom portion is partiall removed as shown. This we term the "sides" waveform.

In Fig. 3 is illustrated how an input display of the capital letter L can be presented in sixteen different ways by the use of equipment based on that described above, and including further simple gating and comparison circuitry as shown in Fig.

5. The circuits shown in Figs. 1 and 2 will, as they stand, produce from the input C shown an output 24 of the type (a) or (b). These differ oniy in the depth of the "shadow" and this variation is obtained by adjusting the reference 22, or alternatively the attenuation introduced by the attenuator 1 6.

In Fig. 3 the normally-white caption on a black background has, of course, had to be shown as black on white.

The way in which the outputs (a) and (b) are generated may be seen by reference to Fig. 4.

Here are shown the waveforms at the input, the output of the attenuator 1 6, the output of the OR gate 14, and at the circuit output 24 on a number of successive lines. It is assumed here that the input takes the form of a simple letter I or upright bar. It is further assumed that the I is five lines high and four picture elements wide, and the delay provided is one line plus one picture element. If the input has an amplitude of unity, then the attenuator substracts one-quarter from all positive values on each recirculation, and the reference value is in case (a) set at five-eighths and in case (b) at three-eighths. The figure illustrates the production of the two outputs (a) and (b) of varying depth. In each case the character is extended downwardly and to the right.

Referring again to Fig. 3, the other key waveforms are derived making use variously of the logic circuits shown in Fig. 5.

Waveforms (c) and (d) are generated by gating the inverse of the caption signal, C, with the key waveform K shown at (a), in an AND gate as shown at (i) in Fig. 5. Waveforms (e) and (f) are generated by gating C and K in an exclusive-OR gate as shown at (ii) in Fig. 5.

It will be seen that (g) and (h) are the outline waveform 0 shown in Fig. 2.

Waveforms (i) to (I) are derived by logically combining in an OR gate the original caption C and one bit of the parallel n-bit recirculating data.

In (i) and (j) a high order bit is used, whereas in (k) and (I) a low order bit is employed. The selected bit may thus be regarded as a further output of the Fig. 2 circuit.

Finally waveforms (m) to (p) make use of the "sides" waveform S shown in Fig. 2. To produce (m) and (n) the sides waveform S is gated in an AND gate with the inverse caption signal C, as shown at (iii) in Fig. 5. For waveforms (o) and (p) the inverse sides waveform S is gated in an AND gate with the key waveform K, as shown at (iv) in Fig. 5.

The waveforms thus obtained can be used in combination to build up an enhanced caption. To take just one example the original caption C, and waveforms (m) and (o) could be used to control red, green and blue video signals respectively to display a three-dimensional letter L in which the front of the letter was red, the sides green, and the bottom blue.

While the invention has been described in relation to alphanumeric characters, it can be applied generally to graphic displays.

Claims (14)

Claims

1. A method of enhancing television pictures or like displays produced by raster scanning, comprising the steps of logically combining an input signal representing the region of the display to be enhanced with an attenuated and delayed signal, delaying the resultant combined signal by approximately one line period and attenuating it to provide the said attenuated and delayed signal, and comparing the combined signal with a reference to provide an output key signal in dependence upon the result of the comparison.

2. A method according to claim 1, in which the delay period is adjustable.

3. A method according to claim 1 or 2, in which the key signal is generated in dependence upon which of the combined and reference signals is the greater.

4. A method according to any preceding claim, in which an output is provided when the reference and combined signals are substantially equal.

5. A method according to any preceding claim, in which a further output is provided in dependence upon the relation of the delayed and undelayed signals.

6. A method according to any preceding claim, in which two or more of the input signal, the output key waveform, and another output, are logically combined to produce a modified output waveform.

7. A method of enhancing a display, substantially as herein described with reference to the drawings.

8. Apparatus for enhancing television pictures or like displays produced by raster scanning, comprising combining means for logically combining an input signal representing the region of the display to be enhanced with an attenuated and delayed signal, means for delaying the resultant combined signal by approximately one line period and for attenuating it to provide the said attenuated and delayed signal, and a comparator for comparing the combined signal with a reference to provide an output key signal in dependence upon the result of the comparison.

9. Apparatus according to claim 8, in which the delay period is in the range H+2p where H is one line period and p represents one picture element.

10. Apparatus according to claim 8 or 9, in which the delay period is adjustable.

11. Apparatus according to any of claims 8 to 10, in which the comparator generates the key signal in dependence upon which of the combined and reference signals is the greater.

12. Apparatus according to any of claims 8 to 11, in which an output is provided when the reference and combined signals are substantially equal.

13. Apparatus according to any of claims 8 to 12, including means for providing a further output in dependence upon the relation of the delayed and undelayed signals.

14. Apparatus according to any of claims 8 to 13, including means for logically combining two or more of the input signal, the output key waveform, and another output, to produce a modified output waveform.

1 5. Apparatus for enhancing a display, substantially as herein described with reference to the drawings.