Multi-layered display (MLD) units provide a significant improvement over existing single layer display (SLD) units or displays.  MLD units may be used to nest display content over spacially displaced or stacked layers to provide an enhanced mechanism for information absorption and analysis by users.  An example of an existing multi-layer display is discussed for example in WO9942889A.
Reference throughout this specification will also be made to the present invention being used in conjunction with multi-layer displays of the type disclosed in WO9942889A. However, those skilled in the art should appreciate that the present invention may also be adapted for use with other types of MLD units and reference to the above only throughout this specification should in no way be seen as limiting. 
The frequency spectrum of radiation incident upon a detector depends on the properties of the light source, the transmission medium and possibly the properties of the reflecting medium.  If one considers the eye as a detector the human visual system can sense radiation that has a wavelength between 700 nm and 380 nm.  Hence this is described as the visual part of the electromagnetic spectrum.  Humans perceive certain frequency distributions as having different colours and brightness.  A scheme was devised to describe any perceived colour and brightness via adding three basis spectral distributions with various weights.  For example in the 1931 CIE colour space any perceivable colour may be described by the following equation:C=xrX+yrY+zrZ 
Where C is the colour being described, Xr, Yr and Zr are the weights and X, Y and Z are 1931 CIE tristimulis curves which are graphs of the relative sensitivity of the eye Vs wavelength.  For any given colour, the weights may be determined by the following equations:xr=∫C(λ)X(λ)d(λ)yr=∫C(λ)Y(λ)d(λ)zr=∫C(λ)Z(λ)d(λ)
The 1931 co-ordinates are formed via the following normalisation:
            x      r        =                  X        r                              X          r                +                  Y          r                +                  Z          r                                y      r        =                  Y        r                              X          r                +                  Y          r                +                  Z          r                                z      r        =          1      -              x        r            -              y        r            
These may be plotted on the 1931 CIE diagram.  The spectral locus defines the pure spectral colours, that is the perception of radiation with a specific wavelength.  Colour co-ordinates that are closer or farther from pure spectral colours are described as being more or less saturated respectively.  The value of the y coordinate is also referred to as the luminance or the variable L.
Pixels on a transmissive display, that is a display that channels light from a rear mounted source, will be capable of maximum and minimum luminous states.  If one labels the maximum state as Lb and the minimum as Ld then the contrast ratio is described by
      C    r    =            L      b              L      d      
The perception model described above accurately predicts that colours on displays can be formed by mixing small areas of three basis colours with modulated intensities which are close in either spatial or temporal proximity.  If the basis colours are plotted on the CIE diagram then the enclosed triangle contains all the colours producible by the system.  The enclosed area is called the colour gamut and hence a display with a larger area can display a greater variation in colour and has a greater colour gamut. 
There are two main types of Liquid Crystal Displays used in computer monitors, passive matrix and active matrix.  Passive-matrix Liquid Crystal Displays use a simple grid addressing system to supply the charge to a particular pixel on the display.  Creating the grid starts with two glass layers called substrates.  One substrate is given columns and the other is given rows made from a transparent conductive material.  This is usually indium tin oxide.  The rows or columns are connected to integrated circuits that control when a charge is sent down a particular column or row.  The liquid crystal material is sandwiched between the two glass substrates, and a polarizing film is added to the outer side of each substrate. 
A pixel is defined as the smallest resolvable area of an image, either on a screen or stored in memory.  Each pixel in a monochrome image has its own brightness, from 0 for black to the maximum value (e.g. 255 for an eight-bit pixel) for white.  In a colour image, each pixel has its own brightness and colour, usually represented as a triple of red, green and blue intensities.  To turn on a pixel, the integrated circuit sends a charge down the correct column of one substrate and a ground activated on the correct row of the other.  The row and column intersect at the designated pixel and that delivers the voltage to untwist the liquid crystals at that pixel. 
The passive matrix system has significant drawbacks, notably slow response time and imprecise voltage control.  Response time refers to the Liquid Crystal Displays ability to refresh the image displayed.  Imprecise voltage control hinders the passive matrix's ability to influence only one pixel at a time.  When voltage is applied to untwist one pixel, the pixels around it also partially untwist, which makes images appear fuzzy and lacking in contrast. 
Active-matrix Liquid Crystal Displays depend on thin film transistors (TFT).  Thin film transistors are tiny switching transistors and capacitors.  They are arranged in a matrix on a glass substrate.  To address a particular pixel, the proper row is switched on, and then a charge is sent down the correct column.  Since all of the other rows that the column intersects are turned off, only the capacitor at the designated pixel receives a charge.  The capacitor is able to hold the charge until the next refresh cycle.  And if the amount of voltage supplied to the crystal is carefully controlled, it can be made to untwist only enough to allow some light through.  By doing this in very exact, very small increments, Liquid Crystal Displays can create a grey scale.  Most displays today offer 256 levels of brightness per pixel. 
A Liquid Crystal Display that can show colours must have three subpixels with red, green and blue colour filters to create each colour pixel.  Through the careful control and variation of the voltage applied, the intensity of each subpixel can range over 256 shades.  Combining the subpixel produces a possible palette of 16.8 million colours (256 shades of red×256 shades of green×256 shades of blue). 
Liquid Crystal Displays employ several variations of liquid crystal technology, including super twisted nematics, dual scan twisted nematics, ferroelectric liquid crystal and surface stabilized ferroelectric liquid crystal.  They can be lit using ambient light in which case they are termed as reflective, or backlit and termed Transmissive.  There are also emissive technologies such as Organic Light Emitting Diodes, which are addressed in the same manner as Liquid Crystal Displays.  These devices are described hereafter as image planes. 
Another subset of LCDs, known as “transflective” or partially reflective displays, is important to consider.  In this application, a portion of the rear part of the liquid crystal subpixel cell (either internally or externally) is coated with a light reflecting material.  The coverage achieved by this reflector material may comprise from 20% to 30% or more of the total active (light transmitting) area of a given subpixel.  Any incident light on this part of the cell coming from a rear-mounted backlight would not be able to reach the viewer's eye unless it were diffused and re-reflected in another spot.  However, the equivalent portion of ambient light from overhead fluorescent lighting or even the sun would pass through the cell's colour filter and liquid crystal layer to be reflected (after appropriate greyscale modification) back to the user.  This system allows portable colour (or even monochromatic) displays such as Tablet PCs, PDAs, and even cell phones to be easily readable even in the harshest of ambient lighting environments without requiring the energy drain on a battery produced by an emissive backlight. 
Common to the display marketplace are “emissive” displays such as CRTs where the luminance of a characteristic colour, shade and brightness is derived from electronically excited photon emission at the subpixel site itself.  There are other emissive display technologies which are consistent with this description such as those based on Organic Light Emitting Diodes (OLEDs), Electroluminesce (EL), and plasma.  Each of these technologies can be used in conjunction with an overlying transmissive (or even transflective) liquid crystal display to achieve a Multi-Layer configuration. 
No known reproduction process can exactly capture the original elements in a given situation (e.g. the brightness of the sun shining down on a landscape).  All colour reproduction systems can hope to do is replicate the relative differences between objects in the original view.  The ratio of the whitest point to the blackest point in a scene is know as its dynamic range, which must be reproduced on some medium such as film, a CRT, an LCD, or paper.  The characteristics of this medium, or its “native response,” will determine the level of success a given reproduction achieves.  The number of steps, or grayscale, into which this dynamic range can be subdivided determines the resolution of a particular primary colour.  A typical monitor system will have the ability to display 8-bits, or 256 shades per primary colour for a total of over 16.7 million colours (256×256×256).  This is known as the colour depth or image palette of the display system. 
All display mediums, especially CRTs, introduce some amount of distortion, which has to be corrected to make the reproduced image look “proper.”  The human eye sees logarithmically.  To compensate for this, playback or image reproduction media must mimic the human visual response curve so that the display shows information in a way we are used to seeing.  The resulting response curve varies in an exponential manner known as the “gamma curve” which is a polynomial equation describing any point on a curve native to a particular monitor.  In a typical imaging system, the brightness changes very little at the lower energy grey levels causing some compression of the shadow detail where our eyes are the most sensitive.  So instead of a straight-line, linear response where there is an equal amount of output for every value of input, the curve has a long, shallow beginning before it begins to climb. 
Video or static images or scenes that are created, edited, stored, and then presented on flat panel media which displays them according to the luminance or brightness values which the author or editor imparts to them.  Once they are imprinted and/or duplicated, further changes to the luminance properties of the content being displayed are only possible if applied to ALL the content.  Until now, no method has been devised for controlling individual portions of a given scene, frame, or series of frames in a prescribed, dynamic fashion.  Such a device or method would be useful. 
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference.  No admission is made that any reference constitutes prior art.  The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents.  It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country. 
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning.  For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements.  This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process. 
It is an object of the present invention to go at least some way towards addressing the foregoing problems or to at least provide the public with a useful choice. 
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.