Digital Color
April 6, 2004
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Interior Architecture Course
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Interdisciplinary
Examples
Color on computer revolutionary
As sketchpad too, for work in other media
To take full advantage of power of digital color, helps to know some of the basic concepts behind it.
Much still not known about color vision…
You can play with this software yourself…
Making a wide range of colors out of only three “primary” ones, a theme throughout color theory and
 very important for digital color: all color on the computer described in terms of amounts of RG&B (in code and screen phosphors) or CMY (K) for printing…
Unlike music or tastes, colors combine and we don’t sense their components…
More total energy—brighter the color
In real life, don’t get to white so quickly
White light plus red = pink, not white…
Additively, the more you picture gets white,
Subtractively: more your pictures gets black (or in real life usually a horrible muddy green color…)
If you truly only use three colors –as in process printing, cmy are best. For painters, rgb works because you usually have tubes of many colors, not all of which are mixture of rby at all…
Pink light, yellow paint = red light
Cyan filter, white paint, mag light
Additive and subtractive can seem to be two different worlds but really two ways of looking at the same thing—different wavelengths reaching your eye. Some might come from a light course—example in room—some come from an object reflecting light (--example in room. )
One color light on white board.
Make white light (y and b)
Cyan board, b,y lights.
Yellow light, cyan board: cyan is absorbing non-cyan colors, namely red (b and g make cyan)
Yellow light is r + g mixed. When the red part is absorbed, result I green.
Filter is subtractive—filters out some wavelengths (everything but the color of the filter…)
Y light, white surface, no filter
Y light, white surface, M filter. =- red light (absorbs g let s r through)
You can play with this—point is that light emitting, reflection, absorption is taking place all at once in the real world.
Opacity of 50% takes half of color and half of the color already on page and averages them.
 You can get lighter or darker—doesn’t tend toward white or black.
Multiple, exclusion, etc all ways of mixing (or compositing as its called in the computer world) colors. All designed by programmers, none necessarily related to any real-world phenomenon like paints or paints.
Natural media programs do better simulate real world mixing—Painter’s magic markers, for instance, and you get to black pretty quickly.
Really whole other topic…
Icc profiles
Circle shows hues and saturation (mixing to white or black) but not =value.
Need three parameters to fully describe a color. Can use RGB (like the eye…) or translate these into HSB (alvy) which can be much more intuitive to choose from. Also Alvy’s HWB (hue-white-black) space.
Can envision such spaces as cubes with axes of RGB (here) : show real cube and relate to upper right.
PASS AROUND CUBE
Relate to Photoshop color picker.
 
Axes are HSV : all hues along one axis, value (or brightness) along another, and saturation along the third.
Used in Painter…
You can make your own color space—doesn’t represent actual geometry of color, just a useful visualization of color relationships.
Any colors on a circle around the middle axis have the same perceived brightness. Not true of standard color pickers.
Help to get feel for the 3D space. Different visualization techniques: ribbons, floating “snow”.
Barb Meier
VIDEO
One draw back of these geometrically simple (and easy to program) spaces is that they are not perceptually correct. It they don’t take into account perceptual differences in color: for instance, many more shades of blue can be distinguished, but these show same number of shades of both blue and yellow (of which few can be distinguished).
Don’t know anyone who uses this picker.
Take home message: If you choose two colors in Photoshop that have the same B (brightness) value, they may well not look equally bright to you.
Not going to get into how this space was devised, but Photoshop's Lab space is a CIE space and Photoshop uses it as a way to translate between different color “modes”: RGB, CMYK, grayscale…
This useful for showing why, no matter how much effort you spend color matching, some colors will never look the same printed out as on the screen. Monitor gamut, in blue, much large than printer gamut. Film much gamut than printing,
From Foley, van Dam
Many of these guidelines apply to non-computer applications as well
Figure 8. MRI Data with Rainbow, Isomorphic, Segmented and Highlighting Colormaps.
In Figure 8, we revisit the MRI data shown in the second row of Figures 2 and 6.  Again, the rainbow colormap in the upper left of Figure 8 creates perceived contours which do not reflect discrete transitions in the data.  Structures in the data which fall within one of these artificial bands are not represented, and attention is drawn to the yellow areas because they are the brightest, not because they are in any way the most important. 
The isomorphic colormap (upper right) is designed to produce a faithful representation of the structure in the data.  A different isomorphic colormap from the one employed in Figure 6 is used.  It has greater variation in hue, although still dominated by variation in luminance, in order to show the structure of lower spatial frequency features (e.g., a tumor near the center of the image). 
The segmented colormap (lower left) is designed to delineate regions visually.  Given the higher spatial frequency of the MRI data compared to the pollution data, fewer segments are employed so that they can be perceptually discerned. 
The highlighting colormap (lower right) is designed to draw the users' attention to regions in the image which have certain characteristic features, such as a tumor (lower right). This colormap was designed to draw attention to areas which have data values near the median of the range.
Tufte also…
demo
Color in real 3D space is influenced by material properties (texture, etc)
By rendering methods
Many material’s colors cannot be accurately depicted yet—complex reflections/diffraction in oil, color from surface of skin… etc.
Very difficult to predict color effects in 3D…
One of the ways that digital color can help is by mathematically simulating real-world color: light and material interactions and effects that change as you view them from different angles.
Many computer-generated images lack subtle color effects. Even ray traced images, which can look very realistic , often have a harsh feeling.
Radiosity: calculates all the light energy in the room as it bounces off all of the surfaces. Very “computationally expense” as they say in the CS world…  beautiful results.
Possible now to do very good simulations of light effects and experiment with and predict 3D results.
I would think would be a more and more useful tool for lighting design…
 
3D programs also simulate real world lighting. User chooses object colors and materials and light colors --  the results are calculated using algorithms based on real-world additive and subtractive color mixing.
10 years from now, digital color tools will be much more powerful, especially for artists and designers working in 3D and with complex lighting and material considerations.
All the basic concepts we just covered will still apply… even more important since easier to be fooled, have to retain critical judgment…