14
Colour
How the eye sees colour
Colour vision is made possible by cones on the retina of the eye, which respond to different colours. The cones are of three types sensitive to certain bands of light – either green, red or blue. The three responses combine so that, with normal vision, all other colours can be discerned. There is a wide variation in an individual's receptor response to different colours but many tests have established an average response (see Figure 14.1).
Colour television adopts the same principle by using a prism behind the lens to split the light from a scene into three separate channels. Colour analysis in the camera will give the appropriate red, green and blue signals according to the spectral energy distribution of the colour being observed. A fourth signal, called the luminance signal, is obtained by combining proportions of the red, green and blue signals. It is this signal that allows compatibility with a monochrome display. The amplitude of the luminance signal at any moment is proportional to the brightness of the particular picture element being scanned. Colour film negative uses a similar filter technique to expose different layers of emulsion to the different colours of the spectrum.
A TV colour signal is an electrical representation of the original scene processed and reproduced on a TV display monitor. The fidelity of the displayed colour picture to the original colours will depend on the analysis characteristics of the light splitting block and the linear matrix of the video camera, which are designed and adjusted to be displayed on the appropriate phosphor characteristics of the display tube, all of which collectively take into account, and accurately reproduce the average human perceptual response to colour. In practice, the available phosphor compounds that are employed in tube manufacture determine the selection and handling of the television primary colour signals needed to provide accurate perceptual response to a displayed colour picture.
Figure 14.1 Thomas Young (17731829) was one of the first people to propose the three-colour theory of perception. By mixing three lights widely spaced along the spectrum he demonstrated that he could produce any colour (and white) visible in the spectrum by a mixture of three, but not less than three, lights set to appropriate intensities. The choice of suitable wavelengths to achieve this is quite wide and no unique set of three wavelengths has been established. The average three colour sensitive cones in the eye have the response curves displayed here, and all spectral colours are seen by a mixture of signals from the three systems
White balance
In colorimetry it is convenient to think of white being obtained from equal amounts of red, green and blue light. This concept is continued in colour cameras. When exposed to a white surface (neutral scene), the three signals are matched to the green signal to give equal amounts of red, green and blue. This is known as white balance. The actual red, green and blue light emitted when white is displayed on a colour tube are in the proportion of 30 per cent red lumens, 59 per cent green lumens and 11 per cent blue lumens.
Although the eye adapts if the colour temperature illuminating a white subject alters, there is no adaptation by the camera and the three video amplifiers have to be adjusted to ensure they have unity output. Because the colour temperature of different light sources and mixtures of light sources varies, it is essential to select the correct filter and white-balance the camera whenever you suspect a change has occurred. When there is a change in the colour temperature of the light illuminating a potential shot it is necessary to adjust the white balance of the camera. The fidelity of colour reproduction is dependent on the white-balance procedure. If required, the white balance can be deliberately adjusted so that overall the pictures are warmed up to a straw colour or cooled to a bluish tint. This customizing is frequently irreversible and so more extreme colour effects should be left to post-production where the depth and appearance of the image can be assessed on Grade A monitors.
Colour correction
A fundamental problem with location work is dealing with a mixture of light of different colour temperatures. If the light remains uncorrected, faces and subjects may have colour casts that look unnatural and distracting. The two most common light sources on location are daylight, which has a range of colour temperatures but averages around 5600 K, and tungsten light, which is often produced by lamps carried to the location that are approximately 3200 K.
Colour correction filters
There are two basic types of correction filter used when attempting to combine mixed lighting of tungsten and daylight:
1. an orange filter, which converts daylight to tungsten and is most often seen attached to windows for interior shots;
2. a blue filter, which converts tungsten to daylight and is often used on tungsten lamps.
Any correction filter will reduce the amount of light it transmits and therefore a balance must be struck between colour correction and sufficient light for adequate exposure. A filter for full colour conversion from daylight to tungsten will have a transmission of only 55 per cent, which means nearly half of the available light is lost. A filter for full colour correction from tungsten to daylight has an even smaller transmission factor of 34 per cent – it cuts out nearly two-thirds of the possible light from a lamp. This is a more serious loss because whereas daylight is usually more than adequate for a reasonable exposure, reducing the light output of a lamp by blue filtering to match daylight may leave an interior lit by blue filtered lamps short of adequate light.
Figure 14.2 Additive colour system. Nearly the whole range of colours can be produced by adding together, in various proportions, light sources of the three primary wavelengths. This is known as additive colour matching. Some colours that the eye can perceive plot outside the triangle and can not be combined by the use of the three chosen primaries unless the application of ‘negative’ light is employed in the camera processing circuits. Given that the tube phosphor and the ‘average’ perceptual response to colour remains unchanged, the fidelity of colour reproduction will be determined by the design of the circuits handling the mixture of the three colour signals
Altering the colour balance
As well as colour correction filters on lens or lamp, both film and video use filters to adjust colour response. These include filters that give an overall tint to the shot and graduated (grads) filters, which help to control bright skies by having a graduated neutral density from the top to clear filter at the bottom – the graduation can be obtained as a hard or a soft transition. There are also filters with a graduated tint to colour skies or the top part of the frame. They are positioned in the matte box for optimum effect but, once adjusted, the camera can rarely be tilted or panned on shot without disclosing the filter position. There are also skin tone warmers to improve close-ups of faces. This can also be achieved electronically.
Post-production
Both film and video can achieve significant changes in the colour appearance of images in post-production. Video has a huge range of post-production effects available. Film production can grade a negative or a print in processing or when dubbed to video for electronic post production.
Colour as subject
Twentieth-century painting has often employed colour as the primary means of visual communication. In their relationship within a frame, colours provide their own kind of balance, contrast, rhythm, structure, texture and depth, independent of any recognizable figurative subject that may be defined in terms of line or tone. Colour not only has a profound influence on composition, in many forms of image making it is the subject of the composition.
The importance of colour to express emotional states or to create sensations of movement and space has not always been recognized. Up to the early Renaissance period, colour was considered by many art patrons as an embellishment to a painting to be selected from a list of expensive pigments. Colour was added as a beautifying agent and priced accordingly. For many years, painters blocked in the main structure of a painting primarily in line and tone. Colour was used to supplement the linear and tonal expression of ideas. Although painters began to appreciate the expressive use of colour, the scientific investigation into colour theory by Goethe, Helmholtz, Chevreul and others in the nineteenth century provided the stimulus to reinforce or confirm many painter's intuitive understanding of the effects of colour. Eventually, the optical sensations of colour were fascinating enough to be able to provide the very subject matter of a picture.
Monochrome
Both film and TV began as a black and white medium. In fact, film began with no colour, no sound and with very little if any camera movement. The ability to record infinite detail mechanically and the novelty of its ‘realism’ compensated the photographic image for its lack of colour. Television, by adding the ability to witness an event as it occurred, wherever it occurred, could also compensate for the absence of colour.
The legacy of monochrome television
The gradual transition in the 1960s to colour broadcasting and the gradual replacement of black and white receivers with near universal colour reception left behind one legacy of monochrome television. Nearly all broadcast television cameras are fitted, as standard, with monochrome viewfinders. There are exceptions, but the majority of cameras in daily use up to, and including the introduction of high-definition equipment, use monochrome viewfinders to acquire the basic material for colour television.
Camera manufacturers explain this paradox as their inability, so far, to provide a 1.5″ monocular colour viewfinder with sufficient resolution, added to their claim that the cost of doing so would be prohibitive. Despite the vast technological changes that have occurred with the development of television cameras in the last 50 years, the one consistent technique that has remained unchanged has been the need for cameramen to use a monochrome viewfinder even when composing colour pictures.
The spread of the DV camera into broadcasting has brought with it the colour liquid crystal display (LCD) viewfinder, which is often fitted as standard. With these viewfinders, colour can now be seen as integral to the composition of the shot instead of the need for a mental note to remind oneself to take colour into consideration when framing up using a monochrome viewfinder.
Optical viewfinders on film cameras have always provided the opportunity to check the influence of colour on the shot.
Problems associated with monochrome viewfinders
One of the most common misconceptions with this situation is that there is no need for a colour viewfinder except where colour differentiation is necessary, for example sports coverage, snooker, etc. The camera manufacturers believe that the viewfinder is simply there to be used for focus and what they term ‘the adjustment of the picture angle’.
The fact that colour plays a significant part in picture composition is either ignored or conveniently becomes the responsibility of other technicians in the television production chain. After 30 years of transition from monochrome to colour, cameramen remain the last group of black-and-white viewers.
The result of framing a composition in monochrome often results in the over-reliance on tone, mass and linear design as the main ingredient of the composition. If a colour monitor is accessible, then adjustment can be made for the colour component of the shot but only too often, the frame of reference for the composition is the monochrome viewfinder or a small portable low quality colour monitor. Colours of similar brightness such as red and the darker shades of green merge and may be indistinguishable in the monochrome viewfinder and yet, as separate hues, they exercise a strong influence on the composition (see Plates 4 and 5). Saturated red and blue appear much darker in a monochrome viewfinder than their brightness value in colour. A small saturated colour against a complementary background has a much greater impact in colour than its viewfinder reproduction.
To some extent monochrome pictures are more abstract than colour and the effect of the image is different from our normal colour perception. The image can be more streamlined if only tone and line are considered as compositional elements. Many years ago, film cameramen, after years of black-and-white photography, had difficulty in adjusting to the complexity of colour composition compared with the simplicity and control of monochrome. When using orthocromatic black and white film stock, they would often use a pan glass when converting to panchromatic film to assess how the colour tones would reproduce in monochrome. Some still photographers prefer to avoid colour in order to emphasize the form and shape of an image.
Using a monochrome viewfinder, video operators have the reverse problem. They must assess how a monochrome viewfinder image is converting a colour image and if there are colour components in the image unseen in colour in the viewfinder that will disrupt a monochrome composition.
It is possible to demonstrate that a video image has been composed in monochrome by switching out the colour on the receiver. It is surprising how much strength is reintroduced into a shot that was originally composed in black and white when the colour content is removed. The reverse can also be seen when a shot could have been improved if a colour viewfinder had been available in order to actively use colour in the composition in addition to line and tone.
A flat lit scene viewed in black and white gives the impression of lack of contrast and punch whereas the same scene in colour may be much more acceptable than the monochrome rendering suggests. A shot lit with predominantly red light has very little contrast and low modulation when viewed through a monochrome viewfinder. This often provokes an unnecessary struggle by the cameraman using a monochrome viewfinder to provide dynamic compositions using mass and line, which is quite unnecessary when the same shot is viewed in colour (see Plates 6 and 7).
Contrasty lighting may provide compositions with more impact whereas overcast light may give flat black-and-white pictures, although the colour content may help to separate subject material. In a monochrome viewfinder the lack of contrast dilutes the visual strength and without strong light/dark relationships the composition may often appear to be lacking balance or emphasis. If reliance is placed on monochrome viewfinder compositions, some colour combinations may have a striking dissimilarity to the balanced black-and-white compatible image.
Composing with a monochrome viewfinder results in emphasizing contrast, mass and usually the convergence of lines. Colour becomes simply the accidental effect of individual objects within the frame rather than the conscious grouping and locating of colour within the frame. The weight of colour elements are not used to balance the composition and can frequently unbalance the considered monochrome composition of tone and line.
Colour and composition
The faithful reproduction of colour requires techniques to ensure that the specific colours of a scene are reproduced accurately and colour continuity requires that the same colours are identically reproduced in succeeding shots. This is often a basic requirement in most types of camerawork but colour as an emotional influence in establishing atmosphere or in structuring a composition, also plays a vital role in visual communication.
Terms used to describe colour can sometimes lead to confusion. In this account:
hue refers to the dominant wavelength – the colour we see;
value is a measurement of reflectivity on a scale of 1-10;
saturation is the purity of the colour.
The perceived hue of any coloured object is likely to vary depending on the colour of its background and the colour temperature of the light illuminating it. Staging someone in a yellow jacket against green foliage will produce a different contrast relationship to staging the same person against a blue sky (see Plates 2 and 3).
There appears to be a reduction in the perception of ‘colourfulness’ under a dull overcast sky. The muted effect on colour under diffused light can often allow colours to blend and provide a softer pastel relationship and a satisfactory picture, whereas the lack of contrast may produce flat, drab monochrome images.
Sunlight raises the general level of illumination and provides a directional light that, reflected off coloured objects, tends to increase the ‘colourfulness’ of a scene compared with the diffuse light of an overcast sky. A proportion of directional light is reflected as white specular from glossy surfaces and increases the impact of colour. The hard modelling and greater contrast make the scene look more ‘alive’.
The perceptual impact of a coloured object is not consistent but is modified by the quality of the light illuminating it, by reflection, shadow and by its relationship with surrounding colours.
Balancing a composition with colour
Balance in a composition depends on the distribution of visual weight. Mass, relative brightness, line and the psychological importance of a visual element can all be structured to provide visual unity in an image and to provide a route for the eye to travel in order to emphasize the most important element. Colour can be used to balance and to unify an image in many ways (see Plate 7).
An out-of-focus single hued object within the frame (e.g., red), often exerts a strong influence in the composition and may distract attention from the main subject.
Light/dark relationships
As we have seen, the eye is attracted to the lightest part of an image or that part of the image which has the greatest contrast and if colour is reproduced as a grey scale, yellow, after white, is the brightest colour. Depending on their backgrounds, a small area of yellow, for example, will carry more visual weight than a small area of blue. When balancing out a composition attention should be paid to the relative brightness of colour and its location within the frame.
Cold/warm contrast
Many colours have a hot or a cold feel to them. Red is considered hot and blue is thought of as cold. People disagree about how hot or how cold a particular colour may be but the general perceptual consensus is that hot colours advance and cold colours recede. This has a compositional significance of colour as a depth indicator and affects the control of the principal subject. It will take other strong design elements within a shot to force a foreground blue object to exist in space in front of a red object.
The eye naturally sees red as closer than blue unless the brightness, shape, chroma value and background of the blue is so arranged that in context it becomes more dominant than a desaturated, low brightness red. Colour effects are relative and no one set of guidelines will hold true for all colour relationships. For example, the intensity of a hot colour can be emphasized by surrounding it by cool colours. The intensity of the contrast will affect balance and to what part of the frame the eye is attracted.
Strong prolonged stimulation of one colour has the effect of decreasing the sensitivity to that colour but sensitivity to its complementary is enhanced. Looking at a saturated red, for example, for some time and then shifting the gaze to a grey area will provoke a sensation of blue-green. This effect of successive contrast is a result of a process of adaptation by the cones and rods in the eye. Intercutting with shots containing strong saturated primaries may give rise to ‘after’ images of complementary colours (see Plate 1).
Colour symbolism
There have been a number of theories based on general colour association concerning the symbolism of colour. Hollywood cameraman Villorio Storaro used his own colour theory in shooting ‘The Last Emperor’ (1987), where he equated different colours with different moods or atmospheres. The shots at the beginning of the Forbidden City and the family were predominantly orange. He used yellow for personal growth of the young emperor and the realization of personal identity. Yellow was also the royal colour of the Chinese. Yellow dissolved to green with the arrival of the tutor – the arrival of knowledge.
Nestor Almendros used the ‘magic hour’, that moment of the day when the sun has left the sky and the earth and the sky are bathed in a golden light. There were barely 25 minutes each day of this quality of light to shoot the film ‘Days of Heaven’ (1978) but it was considered that the contribution of the emotional quality of the light was worth the extra budget required.
Summary
Balance in a composition depends on the distribution of visual weight. Colour can be used to balance and to unify an image in many ways.
If the weight of colour elements is ignored (or unseen), it can frequently unbalance the considered monochrome composition of tone and line.
A composition framed in monochrome may result in the over-reliance on tone, mass and linear design as the main ingredients of the composition.
Colour not only has a profound influence on composition, in many forms of image making, it is often the subject of the composition.
The perceptual impact of a coloured object is not consistent but is modified by the quality of the light illuminating it, by reflection, shadow and by its relationship with surrounding colours.
The individual response to colour may be a product of fashion and culture, or it may be an intrinsic part of the act of perception.