GB2139037A

GB2139037A - Measuring the amount of unsteadiness in video signals derived from cine film

Info

Publication number: GB2139037A
Application number: GB08306842A
Authority: GB
Inventors: Richard Storey; Ian Childs
Original assignee: British Broadcasting Corp
Current assignee: British Broadcasting Corp
Priority date: 1983-03-11
Filing date: 1983-03-11
Publication date: 1984-10-31
Also published as: GB2139037B; GB8306842D0

Abstract

A measure of the amount of unsteadiness in a video signal derived from cine film (caused e.g. by printing misregistration) is made by delaying (14) signal by a delay of one film frame period to make two consecutive frames available, subtracting (16), rectifying (24), and integrating (26) over one film frame period. Compensation for picture detail may be provided by measuring (52; Figure 3) the high frequency detail in the two frames, adding these values, and using the resultant as divisor in a divider (58) connected to receive the rectified difference signal. The unsteadiness signal can advantageously be used in apparatus which automatically conceals imperfections in the picture arising, e.g. from blemishes on the film. <IMAGE>

Description

SPECIFICATION Measuring the amount of unsteadiness in video signals derived from cine film This invention is concerned with measuring (quantifying) the amount of unsteadiness in a video signal derived from cine film.

Unsteadiness in film pictures can be caused by misregistration of successive images in the camera, during printing, or in subsequent conversion to optical images or to electrical signals. It manifests itself as bodily displacement of the image in a random direction buy a random but usually very small distance, typically a fraction of a video line pitch vertically, or a similar distance in any other direction, this distance being less than the smallest resolvable picture element (or 'pixel').

It may be desirable, for example in apparatus which automatically conceals imperfections in the picture arising from blemishes on the film or caused in the film scanning process, to derive from the video signals relating to them a measure of the amount of unsteadiness manifested between two film frames. The direction of displacement can for present purposes be ignored.

The present invention is defined in the appended claims to which reference should now be made.

The invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a simple form of unsteadiness quantifier embodying the invention; Figure 2 is a block diagram of an improved form of unsteadiness quantifier embodying the invention and which provides compensation for picture detail; Figure 3 is a block diagram showing in more detail one of the detail detectors used in the apparatus of Figure 2; Figure 4 is a position diagram iilustrating the pixel values used in the detail detector of Figure 3.

It should be noted that in this specification the term "frame" is used to refer to the cine film frames, as distinguished from the fields of a video signal.

The unsteadiness quantifier 10 illustrated in Figure 1 has an input terminal 12 for receiving a 625/50 PAL colour video signal. A delay device 14 is connected to the input terminal 12, and a subtractor 16 has one input 18 connected to the input terminal 12 and another input 20 (as shown, the inverting input) connected to the output delay of the delay device 14. Thus the subtractor receives the delayed and undelayed signals. The subtractor 16 forms part of a differencing circuit 22 which also includes a rectifier 24 connected to the output of the subtractor 16.

The output of the rectifier 24 is applied to an integrator 26 which integrates over a film frame period. A sampler/register 28 samples the integrator content at the end of each frame in response to an end-of-frame signal received at an input 30. The end-of-frame signal also resets the integrator 26. The sampler-register circuit 28 provides an output 32 indicative of the measured degree of unsteadiness.

The delay device 14 provides a delay of one cine film frame period. With the 625/50 PAL system and conventional 16 or 35 mm film, normally two video fields are generated from each film frame. The delay 14 is thus a constant delay of two video fields, i.e. one interlaced picture period. The subtractor 16 thus receives signals A and B corresponding to two consecutive cine film frames and determines the difference between these two signals. The modulus of this difference is then integrated over a complete frame scan to provide a measure of the amount of unsteadiness (or motion) between the two video signals. Any differences caused by relative motion between the two frames will cause a finite output from the subtractor 16. All such outputs are made positive by the rectifier 24 and integrated through a full frame period by the integrator 26.

Provided that the motion was less than the smallest resolvable picture element, a pixel, as is normaily the case, the value of the integral will increase with increasing displacement. If the displacement were greater than a pixel the relationship between the value of the integral and the displacement may not be monotonic, but it will generally be non-zero. As noted above, the displacements are in practice usually very small.

The value of the integral which is sampled at the end of a frame period is therefore monotonically related to the unsteadiness displacement between the two input frames. However, it is also proportional to the amount of high frequency detail in the film frames. This arises because a displaced plain area generates a vanishingly small rectified frame difference, whereas a displaced finely-detailed area generates a large rectified frame difference.

Figure 2 shows an improved unsteadiness quantifier 40 normalised for fine detail. The same reference numerals are used for corresponding components as in Figure 1 and these parts will not be described in detail.

The circuit of Figure 2 includes also two high frequency detail detectors 52, one connected to each input of the subtractor 16 so as to receive the two video signals A and B which are being compared. The detail detectors, described in more detail below with reference to Figure 3, measure the amount of detail in the area surrounding the pixels which are appearing at the two subtractor inputs. An adder 56 adds the outputs of the two detail detectors to provide a sum signal which is applied as the divisor to a divider circuit 58. The divider circuit 58 is connected between the rectifier 24 and the integrator 26 so that the dividend is the rectified frame difference signal.

For small displacements the output of the circuit of Figure 2 is monotonically related to unsteadiness and is substantially independent of picture detail.

The two detail detectors 52 are identical and one of them is shown in Figure 3. The detail detector measures the amount of signal variation within one pixel of the point from which a frame difference is taken.

The detector 52 has four delays 60,62,64 and 66 connected in cascade to its input. Delays 62 and 64 are of length T, the time taken to scan a pixel, and delays 60 and 66 are of length H - T where H is the line scan period. These delays give access to signal values immediately above and below the centre value Soo, and a pixel on either side, as shown in Figure 4.

Four subtractors 68,70, 72 and 74 subtract the signal Soo from each of the signals Soi, Solo, S-io and So-i respectively. The outputs of the subtractors are then rectified in respective rectifiers 76,78,80 and 82, and the rectifier outputs summed in an adder 84 which has an output 86 carrying a signal D which is a measure of signal detail. The signal D is thus seen to be given by: D=!S10-S00! +IS-io-SooI+ 5c-i -Soo|+|So1 -Soo|.

As shown in Figure 2, this signal is applied to the adder 56 to form part of the signal which constitutes the divisor in divider circuit 58.

The apparatus illustrated can be used in circumstances where an objective measurement of unsteadiness is required, for example for testing purposes, or as part of apparatus which conceals imperfections in the signal caused by blemishes on the film or caused in the film scanning process. Such apparatus operates by replacing the imperfection by another part of the signal such as that derived from a preceding unblemished frame.

Claims

1. A method of measuring the amount of unsteadiness between two film frames from video signals relating to the two frames, comprising forming the rectified difference between the two video signals relating to the two film frames, and integrating the resultant difference signal over a period of at least a substantial part of a frame period.

2. A method according to claim 1, in which the rectified difference is compensated in respect of picture detail.

3. A method according to claim 1 or 2, in which the video signals relate to consecutive film frames.

4. Apparatus for use in the method of claim 1, comprising differencing means having first and second inputs for receiving first and second video signals relating to first and second film frames respectively for subtracting the instantaneous values of the first and second video signals and rectifying the resultant thereof, and integrating means coupled to the output of the subtraction means for integrating the output of the subtraction means over a period of at least a substantial part of the frame period.

4. Apparatus for use in the method of claim 1, comprising differencing means having first and second inputs for receiving first and second video signals relating to first and second film frames respectively for subtracting the first and second video signals and rectifying the resultant thereof, and integrating means coupled to the output of the subtraction means for integrating the output of the subtraction means over a period of at least a substantial part of a frame period.

5. Apparatus according to claim 4, including a compensation circuit coupled between the differencing means and the integrating means for compensating in respect of picture detail.

6. Apparatus according to claim 5, in which the compensation circuit comprises a divider circuit connected to receive as divisor the output of one or more high frequency detail detector circuits for detecting detail in one or both of the video signals.

7. Apparatus according to claim 4, 5 or 6, in which the first and second inputs are coupled to the input and output of a delay device.

8. A method of measuring the amount of unsteadiness between two film frames, substantially as herein described with reference to the drawings.

9. Apparatus for measuring the amount of unsteadiness between two film frames, substantially as herein described with reference to the drawings.

Superseded claims 1,4 New or amended claims:

1. A method of measuring the amount of unsteadiness between two film frames from video signals relating to the two frames, comprising forming the instantaneous rectified difference between the two video signals relating to the two film frames, and integrating the resultant difference signal over a period of at least a substantial part of the frame period.