PART 1. THE DIMENSIONS INTRODUCE
PART 1. THE DIMENSIONS INTRODUCED
1.1 Colours in Space
Hue, Lightness and Chroma 色相，亮度和色度
Hue, Lightness and Chroma
All painters, whether working in traditional or digital media, are in a real sense navigators in space. Whether they are aware of it or not, each touch of colour they apply can be considered, using various systems, as a point within a space defined by three dimensions.
作为图像工作者，不论是传统的还是数码的，都在一个真实的感知空间中。不管他们有没有意识到这一点，每一个他们想用的颜色，都可以定义为三维空间中的一个点。
Figure 1.1.4. Attributes for colours perceived as belonging to (A) objects and (B) light. Saturation refers to purity of colour of light, and can vary throughout its range (white to monochromatic) at any level of brightness; it is represented in B by the angle from the neutral axis. Colourfulness refers to strength of colour of light, and can be thought of as saturation times brightness; it is represented in B by the distance from the neutral axis. Chroma (strength of colour of objects) depends on the colourfulness (saturation and brightness) of the light given off by an object for a given level of illumination. Chroma is necessarily zero at maximum and minimum value (white and black respectively), and reaches its maximum range at intermediate value levels.
Lightness and chroma apply to colours of objects seen in nature or depicted in an image, as well as to colours of an image itself. This is true whether the image surface reflects light (e.g. a photograph, painting, or projector screen), transmits light (e.g. a stained glass window) or emits light (e.g. a computer monitor or TV screen). However, areas of the visual field occupied by objects can also be seen as light, and thus the dimensions of brightness, saturation, and colourfulness apply not only to primary light sources but also to the light remitted by non-luminous objects to our eyes.
Painting Colours in Space
discusses the "colour wheel" and the tonal scale, but typically these are either not related to each other, or they are integrated in a very simplistic way, as in the colour sphere of Johannes Itten. Many painters thus spend much time making up elaborate paint mixing charts without attempting to visualize the series of mixtures they generate as paths through colour space, and so tend to rely colour "recipes" obtained by examining their mixing charts to see how they mixed a particular colour previously. Lacking a conscious three-dimensional conceptual framework for colour, many painters vaguely think of colours being "warmer" or "cooler", without troubling to consider what they mean in terms of the more precise attributes of hue and chroma. Traditional colour theory typically offers little guidance on the physical principles involved in creating effects of light and shade, which require the framework of colour space for their full explanation, and instead relies on crude and inaccurate formulae, such as "get the shadow colour by adding the complementary colour" and so on. A hallmark of traditional colour theory is the admonition "Don't use black!". The real problem is not the black paint, but the painter's inability to visualize any unintended effect of adding black paint as an easily corrected shift within colour space (Fig. 1.1.6).
Students who have previously been exposed only to traditional colour theory are frequently astonished when they first learn to think consciously of their colouring activities as maneuvering through a three-dimensional colour space. A three-dimensional conception of colour assists painters by providing a framework (1) for observing colour relationships, (2) for selecting and mixing colours, and (3) for creating colour relationships from the imagination.
1. As a framework for observing colour relationships.
Painters trained in the concept of colour space do not try to copy each colour in their subject in isolation (the strategy of every beginner). Instead, they use the concept of colour space as a frame of reference for grasping thebrelationship of each colour to the totality of colours present. Tonal realist painters, for example, typically observe colour relationships in the light from their subject, and then, by a process of either conscious or unconscious translation, identify each individual colour in terms of the hue, value and chroma of the paint colour they will need to use in order that the whole ensemble replicates the visual appearance of the subject as closely as possible. In practice, this usually involves first selecting the most important ten or so colours in the subject, and finding the place of these in relation to each other (Fig. 1.1.5). This begins the process of building what I call a scaffolding for progressively finding the place of all remaining colours, most of which can usually be considered as variations on, or intermediates between, these scaffolding colours.
Figure 1.1.5. : Left: Lyndall by David Briggs, 2005, oil on canvas. Right: plan view (above)
and side view (below) of ten selected colours from the image plotted in YCbCr space using
the programme ColorSpace by Philippe Colantoni.
2. As a framework for selecting and mixing colour.
Artists who think in terms of colour space do not need to remember recipes for mixing colours: they understand that most colours can be mixed from any number of combinations of paints, as long as the target colour is within the three-dimensional gamut of those paints. They literally visualize colour mixing as moving colour from place to place through colour space. They decide on the changes in hue, chroma and lightness required, and predict in advance what effect various additions are are likely to have. These crafty painters can mix every colour they want very quickly and accurately, particularly if they equip their palette with a series of strings of pre-mixed pools of colours at various values. This approach to colour mixing was developed to an elaborate degree by the influential mid-20th century American teacher Frank Reilly, whose approach has been described in books by his ex-students including Apollo Dorian, Frank Covino, Jack Faragasso and Angelo John Grado.
Figure 1.1.7. Imaginary sphere under three imaginary light sources, painted as three layers in screen mode (one for each light source). David Briggs, 2007, Photoshop CS2.
Many painters think of colour space in terms of relative hue, lightness and chroma, but there others who train themselves to think in terms of absolute scales of these dimensions such as those of the Munsell Book of Color (q.v. Graydon Parrish and Steve Linberg's Classical Lab). The glossy version of the Munsell "big book" is favoured over the matte version among oil painters because paint mixtures can be tested on the individual removable colour chips and then wiped off safely. Painters who stop short of going the full Munsell often find it very helpful to at least think of lightness in terms of an absolute scale of some kind. In the remainder of this introductory section we will examine each of the major dimensions or attributes of colours in turn, but in order to really understand our subject we must first take up the thorny question of what these "colours" actually are!
Modified February 19, 2017. Original text here.
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