Color Integrity from the Viewpoint of Artistic Painting
Here we explore some very basic techniques used by artists painting in colors. Do not worry if you are not familiar with artistic painting as this will be very fundamental and simple, using techniques artists have known for centuries. Although photographers rarely if ever use these techniques directly, knowing them is essential to understanding how photographic color works. If you do artistic painting please bear with me as my terminology may differ from your own and my description of these basic techniques may have a different emphasis.
We will paint in color the following object, a ceramic bell:
The first basic technique that interests us is preparation of a base shade of a color to be used for the bell. To do this, we may start with a quite pure color directly from a paint tube or we may blend colors from paint tubes to get a source color which typically is fairly intense. As examples here we choose a blue and a bronze:
Next we prepare a "base color" for the bell. We mix the source color, with white and perhaps with black until we get the correct tone of the bell for areas that are directly illuminated; that is, the tone for the brightest fully colored area of the bell that does not show glare. This gives us our base color. Here the source colors have just had white added to produce the base colors.
The shape of the bell leads to shadow or shading of the areas of the bell which are not as directly illuminated. To produce the correct tone for the shadowed areas the artist mixes black paint into the base color; progressively more for the areas in deeper shadow:
This adding black is one of the two key steps in producing tones which are visually correct. The shadow areas are produced by adding black to the base color. The artists among you will know that while this is true, in practice a dark color is often used in place of black. That slightly advanced technique works just as well but includes more than we wish to at this point. The important thing to understand here is that all tones in the complete shading are produced by the blending of just two elements, the base color and either black or a dark color.
In the above bells, the brightest highlights are colored, which does not look right. They should be white. Rather, the brightest areas should be white but the surrounding slightly less bright areas should show some color. The artist handles this by going back to the base color and adding white to it:
All of the affected highlights in the bell are produced by this mixing of the base color and white (or very light gray). The resulting bell looks like this:
Again, all the tones are achieved by mixing just two paints, the base color and white. So, this means that all the tones in each bell are completely controlled through the use of just black paint and white paint.
Of course few objects have just one base color:
The same methods work for each color in an image. Mix the base color and black to produce shade and shadows for areas below full illumination on an object, mix the base color with white, sometimes with a little black added, to produce highlights that contain glare (specular reflections).
The fact that this works just the same for any color in an image is of particular interest to photographers. Since the methods work for each color in an image they also work for the Red, Green, and Blue primaries so widely used in photography. This is very important.
Through the centuries artists have come up with many variations on these basic methods, including many different ways of achieving the blending of paints. For instance an artist may observe that the light falling on the shadow areas of a subject has a brown or green or blue cast compared with brightly lit areas and so will use a very dark brown or very dark green or very dark blue instead of black in order to mix the shadow tones. The artist also has several different ways to do the actual mixing. While the use of these basic techniques varies from artist to artist, the basic principles we have covered above have been extensively and very successfully used for centuries and we will leave further discussion of variations to the artist painters.
There is another artistic technique that is of great importance to us, however. When an artist wishes to show a scene in hazy conditions or partially in fog, it is normally done using white paint. (Actually it may be slightly tinted white paint instead for effects like blue haze, but at this point we want to avoid tinting and so will use white.) With glare or specular reflections we added successively more white to the color as we went into successively brighter areas of the glare. Within an area covered by fog of a particular density we will add the same amount of white to each color regardless of the color or how dark or light it is. There are numerous ways to do this and here we will use a simple, direct technique. The easy way to produce a fog effect in a painting is to first do the painting with normal unfogged colors and allow it to dry. Then paint over the fogged parts of the scene with a light wash of white paint, so that the original scene shows through. The amount of white added varies with the depth of the fog, so we may use more white for more distant areas, or areas closer to the ground. In any one area of the painting where the fog level is constant, however, the same amount of white is applied for any color and whether light or dark:
In this example, some of the foreground objects do not have the white fog effect. But the above images are misleading. The appearance is that a pretty good fog effect has been added to the image on the right by adding white to the fog area. However, the image on the right is really the original. What actually was done was to remove white from the image on the right, producing the nearly fog-less image on the left! Adding and removing white is equally as effective going in either direction.
Artists usually prefer actually mixing paints to achieve fog effects. Instead of the "wash" technique described above an artist may take some base color and some black and mix the two in varying amounts as required for the painting. Then an even-width thick strip of the shaded color is put on the palette, varying from dark to light along the length of the strip. A thick strip of white of the required width is laid along side and the two strips blended across. Using the same method and strip sizes for other colors puts the same amount of white into each shade of the blended black and colors, as required to produce the fog effect. Paint may be used freely as required from any point along the blended strips in building the painting. Again, more white can be added to the mix when painting areas in deeper fog.
All of the above "paintings" have been simulated in Photoshop. This was not easy to do with precision but within the confines of jpeg and gif images, the images are generally close to being accurate.
Perspectives and Comments
Genesis of the Idea what led to the discovery of these simple facts.
Why We Give Few Illustrative Examples of Color Integrity
Color Integrity from the Viewpoint of Artistic Painting.
Color Integrity from the Viewpoint of Basic Physics and Mathematics.
Trying to Deal With Color Integrity in Photoshop
Color Integrity and Color Balance A Few Examples
Comments on Calibrating Digital Images
"Acceptable Accuracy" in Calibration
Calibration and Color Profiling
The Pitfalls of Using Profiling as Camera Calibration
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