GB2204208A - Image signal highlighting - Google Patents

Abstract

An image signal processing system for highlighting a picture defines the spin and position of a notional spotlight 2 relative to the picture 1 and, positional coordinates of successive picture points (x, y). The change of luminance and/or chrominance value of each picture point is evaluated in response to said positional coordinate signals, and the spin and rotation of the notional spotlight for example by solving an equation of a conic section, defined by the axis of the spotlight, b, and the angle and subtended at this axis by the point (x, y). <IMAGE>

Description

IMAGE SIGNAL PROCESSING This invention relates to image signal processing systems for processing video signals.

Video signal processing systems are known which are capable of processing video signals to produce the effect of rotating a picture about any axis (so called spin) or of changing the position, size, or viewing position of the picture. It is also known in some systems to produce the effect of highlighting moving objects in the picture so that they appear to be relecting light from a spotlight.

Object of the present invention is to provide an improved system for producing the effects of highlighting, with a view to achieving flexibility and simplicity.

According to the present invention there is provided an image signal processing system for producing the effect of highlighting a picture, comprising means for providing video signals representing an initial picture, said video signals being provided in sequence in accordance with a raster so that the timing of a video signal is indicative of positional co-ordinates of the corresponding picture point in the picture, means for providing signals to define the spin and position of a notional spotlight relative to the picture, means for providing the positional coordinates of successive picture points in said raster on the occurrence of the corresponding video signals, and means responsive to said positional co-ordinate signals and to said signals defining the spin and position of said notional spotlight to evaluate changes to the respective video signals representing the effect of the notional light beam.

In a preferred embodiment changes to the respective video signals representing the effect of the notional light beam are evaluated by solving for each picture point an equation which evaluates a function of B and cos(alpha) in terms of x and y, where B is the length measured along the axis of the beam from the spotlight to the picture, x and y are the position co-ordinates on the picture of the relevant picture point, and alpha is the angle between the beam axis and the line from the spotlight to the point x, y.

Preferably the equation is the equation of a conic section. Furthermore, means may be provided to selectively set up signals to represent the colour characteristic of the notional spotlight. The system may operate in YUV or RGB colour components, and may also use CMX colour components if the final signals are to be used for printing.

In a preferred embodiment sequences of video signals representing successive picture frames will be provided when using the system, and successive frames may be subjected to manipulation in known manner. The inputs provided to define the spin and position of the notional light source may also be varied from frame to frame so that the highlighting effect can be made to represent a light beam which changes in position, direction, or colour.

The invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figure 1 is a diagram illustrating the. basis for evaluating the changes to be made to each video signal to represent the effect of a notional light beam.

Figure 2 details mathematics illustrating the derivation of a function of alpha and B.

Figure 3 is a block diagram of an image signal -processing system.

Referring to the drawing, in Fig. 1 the plane 1 is assumed to be the plane of a picture to be highlighted by video signal processing. The plane is defined by. z = 0.

The point 2, having co-ordinates (0, 0, bz) defines the position of a notional spotlight, and vector b denotes the axis of the notional beam. It will be understood that, in accordance with the invention, the system is required to make changes to the video signals constituting the picture in plane 1, so as to produce the effect of lighting the original picture with a light beam directed along b from source 2. In considering Fig. 1 it will be assumed that the light from the source 2 has a known composition (colour components) and the mathematical theory is directed to evaluating changes to be made to the colour components of each image point in the picture. Line 3 is the perpendicular from point 2 to the picture plane, meeting the plane at point (0, O,).Point x, y is any picture point in the picture and vector m is the line joining source point 2 to picture point (x, y) while alpha is the angle between b and m. From a consideration of Figure 1 it can be seen that the changes to be made to the video signal for the picture point x, y, will depend on alpha and the length B of vector b. Mathematics illustrating the derivation of a function of alpha and B which is used for evaluating the required changes is detailed in Figure 2.

The factor #2 + y2 + b 2 is assumed to be a constant and subject to this assumption the last equation above can be seen to be the equation of a conic section of the general form:- ( (x-a) k )2 + ( (y-b)k )2 + k + K" xy = B2 cos2 (alpha) x y For any one picture the spotlight position, B2 is constant, so the equation provides a "change" signal proportional to (cos2 alpha). For points (x, y) on a family of eclipses, each one enclosing the preceding one, about the point Px, Py), the change signal will diminish as cos2 alpha. In the example about to be described with reference to Fig. 2 the quantities kx, k , k, k", a and b are y evaluated from the operator controlled input to x the system, for each frame of the picture.The values of x and y are derived for each picture point (dependent upon the time of the picture point in the raster). Then, b2 cos2 alpha is evaluated for each picture point as it occurs and used to change the respective video signal to represent the effect of the spotlight.

The assumption that the factor x2 + y2 + b 2 z is constant is practically acceptable provided the positioning of the spot light is confined so that the angle between b and the plane of the picture does not become too small. Should the angle become so small as to approach grazing incidence if may become necessary to correct for the factor.

Referring now to Fig. 3, reference 10 denotes a video signal processing system arranged to capture successive frames of digital video signals and, in reponse to operator #inputs, produce changes in the video signals to represent changes in the spin, position or other parameters of the corresponding picture. The construction of the system 10 may be for example an Encore system such as manufactured by the present Applicant. When the system is used an output of the processed video signals appears on the leads 11 and, as indicated in the drawing, the video signals comprises three colour components Y, U, V. Colour component signals for each picture point appear sequentially in raster format.In addition to delivering the processed video signal YUV the system 10 delivers to a computer 12, as represented by arrow 13, signals defining the spin and position (and other parameters) of the picture represented by the YUV outputs. The spin and position signals relating to any one picture frame of YUV outputs are applied to the computer 12 at the beginning of the frame period corresponding to inputs made prior to the frame period to represent desired changes in spin, position and other parameters. The means for setting up these operator inputs are denoted by the arrow 14. Means are also provided, denoted by the arrow 15, for making other operator inputs to the system 10 to define the position and spin of a spot light being simulated. The spotlight inputs are in turn passed directly to the computer 12 as represented by the arrow 16. It will be understood that signals representing the position and spin of the notional spotlight to be used in any one frame are those available at the beginning of the frame.

The computer 12 is arranged to evaluate, at the beginning of each frame period and in response to the picture and light inputs, the quantities a, b, kx, k , k, and k" required for evaluating (B2 cos2 alpha) for each picture point during the frame period. It will be noted that the system 10 is capable of imparting spin and position changes to both the picture and the spotlight independently of each other but, as will be apparent from Figure 1, it is the spin and position of the spotlight relative to the picture which is significant in evaluating the change to be made to the video signals to represent the effect of the notional spotlight. The computer 12 is arranged to evaluate these relative quantities from the inputs on 14 and 16 prior to evaluating the quantities enumerated above.

Block 17 represents a circuit for evaluating the position co-ordinates (x, y) of each successive picture point of the video output of 10 as the corresponding colour component signals occur on the leads 11. Signals representing x and y are fed in succession to a calculator 18, which receives continuously throughout each frame period the quantities a, b, k, k, k, k" from the computer 12.

The calculator is set up to evaluate for each picture point in the frame the aforementioned quantity (B2 cos2 alpha).

This quantity is applied to a look up table LUT 19 which is set up to produce a signal which determines the changes to be made to the video signal components for the respective picture point. LUT 19 may be set up for example to convert the input L2 cos2 alpha to a 'change' signal proportional to cos alpha or to some other prescribed function of the input.

The LUT 19 may furthermore be conditioned to effect different conversions dependent on the signals derived from the computer 12, as indicated by the connection 20. The change signal from LUT 19 is applied to three further look-up tables, LUT 21, LUT22 and LUT23.

LUT 21 produces a signal which is applied to a multiplying circuit 23 to multiply the Y component of the respective picture point video signal, producing a change in brightness (luminance) of the picture point. The product output of 24 is then applied to an adding circuit, in which it is added to the output of the LUT 22, to represent the addition of a highlight to the picture point. Therefore LUT 21 is arranged to convert the change signal from LUY 19 into a component which represents the contribution to brightness made by the spotlight, whereas LUT 22 is arranged to deliver a component of the change signal from LUT 19 which contributes highlight. The output of the adding circuit 25 represents the changed Y component of the picture point.

The tables included in LUT 21 and LUT 22 may be derived empirically.

LUT 23 derives from the output of LUT 19 a factor k (dependent on the change signal) which effects changes in the colour of each picture point to simulate the effect of the spotlight on the picture colour. The factor k is applied to an arithmetic circuit 24 which receives, at 25 from the system 10, the U and V component signals of each picture point. It also receives at 25 operator inputs in the form of signals representing the U and V components of the light selected by the operator for the notional spotlight. The U and V components of the light remain constant during any particular frame period.If it is assumed that the U and V components of a picture point represent a colour A whilst the U and V components of the light represent a colour B, the circuit 24 is arranged to produce output signals (which would normally be in the form of U and V components) representing: KA + (1-K) B In this way the effect of the spotlight on the colour of the picture is simulated.

It will be appreciated that the operator inputs to represent the spin and position of the spot light can be changed from frame to frame as well as those for the picture. In this case the successive frames of video signal may represent a moving picture lit by an independently moving spotlight. The colour characteristics of the spotlight and its brightness can also be changed.

The invention, though described as applied to television, can also be applied to so-called graphics systems, intended to process pictures for printing in which colour component signals may be stored as RGB or CYM values.

Claims (7)

CLAIMS:

1. An image signal processing system for producing the effect of highlighting a picture, comprising means for pro#viding video signals representing an initial picture, said video signals being provided in sequence in accordance with a- raster so that the timing of a video signal is indicative of positional co-ordinates of the corresponding picture point in the picture, means for providing signals to define the spin and position of a notional spotlight relative to the picture, means for providing the positional coordinates of successive picture points in said raster, on the occurrence of the corresponding video signals, and means responsive to said positional co-ordinate signals and to said signals defining the spin and position of'said notional spotlight, to evaluate changes to the respective video signals representing the effect of the notional light beam.

2. An image signal processing system according to claim 1 wherein changes to the respective video signals representing the effect of the notional light beam are evaluated by solving an equation for B and cos (alpha) in terms of x and y for each picture point in which B is the length measured along the axis of the beam from the spotlight to the picture, x and y are the position co-ordinates on the picture of the relevant picture point and alpha is the angle between the beam axis and the line from the spotlight to the point x, y.

3. An image signal processing system according to claim 2 wherein said equation of B and cos(alpha) in terms of x and y is the equation of a conic section.

4. An image signal processing system according to any preceding claim including means for selectivley settingup signals to represent the colour characteristic of the notional spotlight.

5. An image signal processing system according to claim 4 wherein the colour characteristic is stored as three components of luminance and two colour difference signals.

6. An image signal processing system according to claim 1 wherein successive picture frames are provided to said system and inputs . provided to define spin andlor position of the notional light source are varied from frame to frame.

7. An image signal processing system substantially as herein described with reference to Figure 3.