Friday, 1 March 2013

OUGD404: Design Principles - Colour Questions

These are the questions which we came up with as a group in our studio session. I decided to research into all of these questions further.

When contrast of extension is balanced, is it a high or low contrast?
When contrast of extension is balanced, there is a low contrast.

Does contrast of extension apply to colours that aren't complementary?
Yes, since carrying out colour experiments I found that even if colours which aren't complimentary are used together, they still form a contrast, as it is always important that we find the correct balance of colours.

Do tertiary colours have a complementary colour?
Yes, every tertiary colour has a complementary colour. They are the opposite colours on the colour wheel.

How does artificial/natural light effect the perception of colour?
This is the question I answered in an individual post.

How does the chromatic value of white stock effect the colour of the print?


1. Absolute luminance. When we perceive brightness or lightness, we fundamentally respond to the quantity of light energy reaching our eyes from objects and surfaces around us. This is the "objective" component of brightness or lightness. The environmental range in luminance values is huge (diagram, right). As a conservative estimate, from the luminance of a white paper under a night sky (about 10-2 candelas per square meter) to the luminance of a 60 watt light bulb (about 105 cd/m2), a ratio of about 1 to 10 million or 107. 2. Response range. In light sensitive media, the response range comprises all luminance values that produce a perceptible change in the media, and a perceptible change if the luminance is either increased or decreased by a proportionally small amount. The response range is bounded by thresholds at high and low luminance values. The lower limit ("noise") is defined as the highest luminance that does not produce a perceptible difference in the light sensitive media if it is reduced, and the upper threshold ("saturation") as the lowest luminance that does not produce a perceptible difference if it is increased. The response range is typically represented as a characteristic curve that shows how relative luminance levels (on a logarithmic scale) are transduced into proportional media densities (on a linear scale).

a characteristic curveillustrating the 1:1000 response range typical of photographic film
For physical reasons, light sensitive electronic and chemical media have a relatively small response range, given fixed optical aperture and exposure times. The best CMOS chips, for example, have a response range somewhat above 104 or 1:10,000; photographic film and video displays have a response range of about 103 or 1:1000 (shown above), and photographic print papers have a response range of less than 1:100 or 102. By comparison, human color vision provides a
large response range that is at least 1:100,000 or 105 at most adaptation levels. 3. Luminance adaptation. Because the response range of all light sensitive media is relatively limited in comparison to the absolute range of luminance valuess in the environment, the exposure of the media to light energy must be adjusted, by means of aperture size, exposure time or filters, so that the environmental luminance values fall within the fixed response range of the media. In a similar way, luminance adaptation shifts the response range of the eye so that the visual system becomes less sensitive when light is very abundant, and more sensitive in the dark. These shifts involve changes in pupil size, changes in the proportion of unbleached photopigment in the retina, and changes in the response sensitivity of visual pathways in the brain.

luminance adaptation
The total light reflected in all directions from a surface, as a proportion of the total light incident on the surface, is called its reflectance. Luminance adaptation is largely governed by the average luminance of the entire visual image, which in almost all environments is the average reflectance of all surfaces, called the adaptation gray. The adaptation gray is usually equated with a reflectance of about 20%.
Roger Clark estimates that scotopic vision corresponds to a photographic ISO of about 800, whereas photopic vision corresponds to an ISO of about 1. This suggests the dimension of visual adaptations between scotopic and photopic vision. Luminance adaptation defines three perceptually unique visual domains: • Scotopic vision is the visual adaptation to night environments, roughly with surface luminance values below 0.1 cd/m2. Scotopic vision provides no chromatic (hue and chroma) sensations at all, so that all surfaces appear to be shades of gray; white surfaces appear to be a silky silvery color, and gradations in lightness below middle gray are indistinguishable. • Photopic vision, at the other extreme, is the visual adaptation to sunlit outdoor environments, roughly with surface luminance values above 300 cd/m2. Photopic vision provides the maximum visual contrast between light and dark surfaces and the maximum sensations of hue and chroma; discrimination of surface colors is good down to very low luminance factors. • Mesopic vision is essentially a mixture of scotopic and photopic adaptations, and is the common luminance adaptation in indoor environments under artificial light or restricted daylight, where white surfaces have a luminance of roughly 10 to 100 cd/m2. Contrast and chromatic variety is muted, moreso as illumination decreases, and there is some loss of discrimination among very dark surfaces. Although the eye is a very poor photometer — human vision is relatively inaccurate at judging the absolute luminance of a scene or object (which is why photographers must meter light exposures) — the different states of luminance adaptation have very recognizable effects within color vision: quality of white – the bright, pure, "saturated" quality of a white surface under photopic illumination changes to shades of gray under mesopic and scotopic vision; colors reflected into white surfaces by surrounding surfaces become more obvious lightness contrast – lightness contrast peaks under photopic illumination, and becomes slightly more muted under mesopic illumination: the perceived contrast between light and dark values is reduced, and we can discriminate fewer steps in a graduated value scale; then the contrast ratio between light and dark values (the visual response range) is fairly constant down to luminances of about 10 cd/m2, and then becomes more restricted. dark value discrimination – the lightness discrimination lost under dimmer illumination falls proportionately more within darker values chromaticity – the colorfulness of colors peaks under photopic illumination, and colors gradually become more muted and darker as illumination decreases; under scotopic illumination color perception disappears entirely and all surfaces appear as shades of gray detail – fine detail, such as text printed in fine type, becomes more difficult to see under low illumination; under scotopic vision we lose foveal vision entirely, and cannot read even large print type, such as newspaper headlines bright luminance – under photopic illumination few lights (often, only the sun and highlights or reflections of its luminance) appear genuinely "bright"; all other lights appear to be merely glowing or "super white"; but under low mesopic and scotopic illumination, even illuminated surfaces, such as the walls of an illuminated room viewed from outside through a window, appear as bright as lights.
a comparison of common light environments (log scales)
where 1 lux = 0.31 candela/m2: the luminance of a white surface equals the illuminance falling on the surface

4. Anchoring. It appears from experimental evidence that the visual system perceives the absolute overall luminance only poorly and slowly, and much of the information about the environmental luminance comes from the apparent contrast among all surfaces, determined by looking at the pattern of lightness differences at each color edge. Because the reflectance of surfaces is always within 1% to 99% (and is commonly within 5% to 95%), the contrast ratio of diffusely reflecting surfaces is typically 1:20 or less. In addition, the most sensitive lightness discrimination across all adaptation states is in light valued or near white surfaces. This typically puts adaptation gray in the lower half of the visual response range. Thus, the luminance that produces a 50% visual response on a characteristic curve may be less than 10% of the luminance saturation threshold. The "excess" visual response capability at higher luminance values is available to handle the "glare" luminance of reflected highlights or the direct imaging of light sources. This produces a perceptual contrast, within the response range at any adaptation level, between lightness and brightness. Lightness is the perception of luminance that is less than the luminance of an area perceived as "white" (diffusely reflecting nearly all the light that is incident on it). As luminance increases above this level, color areas seem to glow or fluoresce, and finally to shine as lights; these perceptions appear subjectively different from surfaces, as brightness. Color vision establishes the boundary between these two sensations through lightness induction. In most viewing situations, lightness anchoring appears to put the "white" response approximately around the middle of the visual response range — as appears, for example, if we fit a plot of lightness values (CIE L*) on log luminance values (CIE Y) over a schematic visual characteristic curve (diagram, below).

schematic location of lightness variations within
visual response range
plot of CIE L* values on log CIE Y values (dark blue) superimposed on schematic characteristic curve (light blue)

This creates a dynamic relationship between the average scene luminance (luminance adaptation) and the perception of white surfaces (lightness induction).
If a brightly illuminated surface suddenly appears in a dark adapted field of view, luminance adaptation will decrease sensitivity in order to shift the luminance range downward within the characteristic curve, and the illuminated area will decrease in brightness enough to permit perception of it as a white surface. Alternately, when entering a dark environment, luminance adaptation will increase sensitivity until the most luminous surfaces in view are near the middle of the response range. The exception seems to be low mesopic and scotopic vision, where physically white surfaces always appear distinctly gray, when compared in imagination to the same surfaces in sunlight. This implies that the lightness range has shifted even farther down the visual response range. Consistent with this fact, we lose discrimination of darker values as light becomes dim, and under scotopic vision cannot see the difference among values below a middle gray. As shown by the characteristic curve, this is because large proportional differences between low luminance values have no effect on the visual response at the bottom of the curve. 5. Relative luminance contrast. The dynamic relationship between adaptation and lightness induction extends rather deeply into lightness perception. A single illuminated surface isolated in darkness can appear to be white, even when it is actually black (very low reflectance). Alan Gilchrist and colleagues have shown that persons looking into a hemisphere that filled their field of view and was painted various patterns of dark gray and medium gray, saw the patterns (after adaptation to the dome illumination) as painted light gray and white (diagram, below).

lightness anchoringleft column: the interior of a large, diffusely illuminated hemisphere was painted with patterns using a dark gray (CIE L* = 25) and medium gray (L* = 55); right column: the perceived gray values were shifted lighter, so that the medium gray value appeared white (L* > 90); after Lee & Gilchrist (1999)
The shift in the perceived lightness does not change the relative lightness contrast between the color areas, so that the luminance proportions seem to be preserved. This shows, among other things, that accurate lightness perceptions require variations in surface reflectance across a representative range of
luminance contrasts. However, the effects of luminance contrast can also be quite local, as shown in the Bartleson Brenneman effect (image, below).

the bartleson brenneman effect
Here the background lightness influences the apparent gradations of gray. A dark background pushes all gray values toward white, compressing their perceived lightness differences; but a light background shifts the values toward black, enhancing the apparent lightness contrast.
6. Scene spatial interpretation. Finally, the dynamically limited, luminance adapted and white anchored luminance variations are imputed by color vision to actual objects, and their surface colors are interpreted in terms of the spatial orientation of their surface to the sources of illumination in the environment, including the relative intensity of light sources, the effects of cast shadows or barriers, the presence of windows, and so on, all of which constitute a spatial interpretation of the scene. Spatial interpretation has a very large effect on color appearance. As a simple example, the first photo (below) shows two sheets of white paper photographed in a spatial context in which one sheet is in shadow and the other in direct daylight. In the two photos below it, the color of the illuminated sheet is copied into the location of the shadowed sheet, or the color of the shadowed sheet is copied into the location of the illuminated sheet.

two sheets of white paper in a spatial context

both sheets of the same "light" lightness
both sheets of the same "shadow" lightness

the effect of spatial context on color
Here the "shadow" color appears much darker when it is located in the illuminated spatial area, and the "light" color appears much brighter when it is located in the shadow spatial area.
These color shifts are not simply due to the relative luminance contrast of the paper colors with the surrounding carpet colors, because the apparent sizes of the color shifts are much smaller when the spatial context is removed and the identical computer monitor colors are presented as two dimensional contrast figures (diagram, below).

spatial context removed from color contrast
I find the contrast between the "shadow" lightness figures, when compared to the two dimensional display, to be especially striking. The spatial image gives the unambiguous impression that the shadowed paper is white and the illuminated paper is a middle gray; but in the two dimensional display the two colors appear nearly the same value.
Overview of Lightness Components. This section has presented the six conceptual dimensions for analyzing, and by means of the analysis viewing accurately, the lightness gradations in any scene. The diagram (below) summarizes how these different components of lightness should be evaluated.

interplay of components in lightness


Does tone affect the temperature of a colour?

Change the color tone of a picture

When color temperatures are not measured correctly by a camera, a color cast (too much of one color dominating the picture) can display on the picture, making the picture look too blue or too orange. You can adjust this by increasing or decreasing the color temperature to enhance the details of the picture and make the picture look better.
  1. Click the picture that you want to change the color tone for.
  2. Under Picture Tools, on the Format tab, in the Adjust group, click Color.
Adjust group on Picture Tools Format tab
Adjust group on the Format tab under Picture Tools
If you don't see the Format or Picture Tools tabs, make sure that you've selected a picture. You may have to double-click the picture to select it and open the Format tab.
  1. To choose one of the most common, Color Tone adjustments, click Presets, and then click the thumbnail that you want.
Tip You can move your mouse pointer over any of the effects, and use Live Preview to see what your picture will look like with that effect applied before you click the one that you want.
  1. To fine tune the intensity, click Picture Color Options.

Is it possible for a colour to be warm if its desaturated?
If a colour is neutral then it is not possible to distinguish the temperature and so it is hard to define whether it is warm or not. It all therefore depends on how desaturated a colour is.
Can complimentary colours be balanced (contrast of extension)?
Yes they can be balanced however contrast of extension requires these proportions of the complementary colors to achieve a balance.

How would simultaneous contrast be used?
It is not so much about how simultaneous contrast can be used, it is more to do with the way we apply it to our work.

How do you make gold and silver?
Metallic pantone swatches are used to make gold and silver.

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