A “normal” image is two-dimensional (2D). All positions on the image can be located by their X and Y coordinates. A three-dimensional (3D) image has another dimension, Z, which is required. In terms of your computer screen, X is horizontal position, Y is vertical position, and Z is the position into or out of the screen. Getting that extra dimension into an image is tough; usually it takes two images from different perspectives to accomplish that, but using two images doubles the image overhead. ChromaDepth® 3D takes a much more efficient approach by using color to carry the Z position information. This is called encoding depth into color. This Design Guide will explain how you can design your own images that will show great 3D when viewed with ChromaDepth® 3D Glasses.
There are two parts to the ChromaDepth® 3D process: designing the colors of an image according to ChromaDepth® 3-D, then presenting and viewing the image with C3D™ Glasses. The first step — designing the colors of the image — is much easier than it sounds. First, you choose a color palette (go to the C3D™ Color Palettes section below for a thorough primer on this). There are different color palettes to produce the best 3D effects for a selected background color. There are probably an infinite number of color palettes that could work, but the simplest and most dramatic is RGB on Black. This stands for Red-Green-Blue on Black Background. In the ChromaDepth® 3D process the color of an image element and that element’s immediate surrounding color determine its Standard depth position. If we keep the background color constant around each image element, then the color of the element alone will determine its Z dimension.
Background Color and Color Palettes:
The choice of background color is the most important factor in determining the colors which should be used to achieve C3DTM effects. The easiest and most commonly utilized background colors are black and dark blue. The color palette, RGB on Black/Blue, apply to both of these background colors. If dark blue is used, it must be a very pure, very dark blue. The effects will not be the same for a sky blue, medium blue, or other light blue. The reasons for this are explained in the section on Tint and Depth Position.
On a black or dark blue background the ChromaDepth® color palette uses red for the most foreground object, dark blue for the most background object, and green for the middle ground. The other colors fall in between according to the colors of the rainbow. Thus one could use red, orange, yellow, yellow-green, green, blue-green, blue, and dark blue, in order, from foreground to background. An infinite number of colors may be used to divide the space between red and blue. Contoured or rounded surfaces can be shown by smoothly blending from one color to another across the surface. Be sure to use black patterns on the surface to help define its shape; see Use of Black for details.
Another color model that is very effective on a black background is the ‘Patriot’ color model; Red-White-Blue on Black. See the C3D™ Color Palettes page for details.
When a dark blue background is used it is important to incorporate some black pattern on the blue in order to locate the background in depth space. Without a black pattern the blue background seems to be undefined space. he black pattern provides edges for your mind to locate in space, enlarging the apparent depth.
On a white background the ChromaDepth® color palette is the compliment of the color model for a black background. This makes the key colors cyan, magenta, and yellow (CMY; the compliments of red, green, and blue, respectively), so this is called the Cyan-Magenta-Yellow on White color model. The inverse color function on many computer graphic design programs can take a normal black background C3D™ colored image and convert it to a white background, CMY on White ChromaDepth® image. But be warned; although the CMY on White 3D effect is as strong as the RGB on Black 3D effect, the images created with CMY on White sometimes may look unnatural. The RGB on Black color palette follows the colors of nature and of normal artistic design, but try both color palettes.
Using Outlines as Local Backgrounds:
A very good way to simplify dealing with backgrounds is to use black or white outlines around image elements. This effectively gives each element its own ‘local background’, so that no other color can contact the fill color which is inside the outline. The choice of black or white for the outline color depends on the color model used: the outline color should be the same as the background color in that color model. The width of the outline needed will depend on many factors, and can only be determined by a little experimentation. Using outlines as local backgrounds is especially valuable when creating animations in which objects may pass over each other.
Depth Cueing:
Using normal two dimensional depth cues in an image can dramatically augment the depth created by the glasses. These include shading for roundness, perspective and forced perspective effects, overlap, changing size as depth is changed, including shadows of one object on another, and increasing the brightness of colors as objects are brought closer to the foreground.
It isn’t always necessary to change the color of an object as it is moved closer or further in depth. An object moving from the background to the foreground could be designed to increase in size as it moves up the color palette from blue through green, yellow, orange, and red. Once it becomes red, you can continue to force the apparent movement in depth by continuing to increase the size of the object, even though you are no longer changing its color. The strong depth cue created by increasing the object’s size continues to fool your brain into seeing the object move forward even though there is no change in the C3D™ created depth. Similarly, shrinking the size of an object while smoothly changing its color from red down the rainbow to blue will make the object appear to recede into the distance. Continuing to shrink the object after it has reached maximum blue will continue the illusion that it is moving away.
Combining size change with brightness variation can achieve even more dramatic results. Make the object darker when it is supposed to be far away and brighter when it is in the foreground.
With strong two dimensional depth cues it is even possible to keep the sense of real stereoscopic depth while mixing up the colors, such as placing an orange object behind a yellow one by use of perspective and shadows. It does not always work, but it can be worth trying. Be aware, though, that if you try to push this too far the effect may break down.
Avoiding the Image Border:
The border of an image generally appears to be at the middle ground position. Any object colored to appear at middle ground or deeper can be clipped by the border without any visual problem; it looks like the border is a frame above the object, like it is in a shadow box.
Any object that is colored to appear closer than middle ground should be kept away from the border because it will appear to snap down to the border where it touches it, losing the depth effect (incidentally, this is true for all 3D processes, not just ChromaDepth®). Adding a red or black border around the image can reduce this problem. In a moving image a red object can move off-screen across the border if it moves quickly; your mind doesn’t have time to figure out that crossing the border was a problem.
Handling Highlights:
In two dimensional art, highlights from shiny surfaces are normally shown by a white spot or white starburst. This causes a problem for C3D™ images because the color white tends to the middle ground of the image. This means that a white highlight on a blue object will look like it is floating off of that surface, while a white highlight on a red surface will look like a bright point inside of the red surface. Highlights can be used with ChromaDepth®, but they usually are not colored white.
There are two main methods for showing highlights, and they can be combined in different amounts according to taste. The first approach is to select the highlight color to be slightly closer than the surface it is on.
Here is how it works: the highlight on a surface should be just slightly closer than the surface, so it is necessary to use highlights which follow the ChromaDepth® 3D color/depth palette. We have found that using a color which is five (5) percent closer (closer means ‘towards red’) than the highlighted surface is quite effective. For example, if the scene has been divided into twenty depth zones, a five (5) percent closer highlight would use the color of the next closest depth zone. For one hundred (100) depth zones you would move closer by five (5) depth zones for the highlight.
The second method is to keep the color the same as the surface, but to increase the brightness. This works well for TV and video, since the main object colors need to be slightly muted (by adding black to shade them down) to keep them ‘NTSC legal’. NTSC illegal colors ‘bloom’ on the screen, blurring past their intended boundaries. This is fine for a highlight, so using NTSC illegal color brightness for highlights works well to emphasize the extra brightness of the highlight. With a little finesse, these two approaches can be combined with good results.
The Importance of Black and How to Use it:
Black is extremely useful to the C3D™ artist. Wherever possible, black should be used to outline colors which are on a black or dark blue background. In a similar manner, white should be used to outline colors against a white background.
When the human brain compares the differences in the images of a stereo pair in order to determine what depth should be perceived, it is the edges of objects and other high contrast vertical features which are compared. If you want to blend colors across a surface to show roundness or bending, it is very effective to add some black lines into the surface to provide the edges that convey the depth. For example, if you want to show a ball that has roundness, you can blend from red at the closest point around to yellow at the edge, then add black shading or crosshatching lines as would normally be used to indicate roundness in a two dimensional image. If the weight, or thickness, of these black lines is adequate, the lines will allow your mind to see the height differences by the color blending in a very effective manner.
Tint and Depth Position:
In the jargon of color, tint refers to taking a pure color and adding white to it. The resulting lightened color is a tint of the original. Tints can be used to broaden the range of colors which appear to lie at a given depth position and to give textured effects to surfaces. Here is how this works:
We will first presume that we are working with a black or dark blue background. Under these circumstances a white object will appear to be in the middle ground position, equally spaced between the foreground and the background. Adding white to any color ‘pulls’ that color toward the middle ground. The degree to which the color is moved toward middle ground depends on the amount of white added to it. A little white only moves the color a little, much white moves it far. Since the colors are pulled toward the middle ground, each color reacts to tinting in its own way. Reds and oranges move further away, since they are forward of middle ground. Yellow and yellow-green don’t move much since they are already about at middle ground. Greens and blues move closer with tinting, since they are normally in the background, behind middle ground. All colors end up at middle ground as they are tinted completely to white.
An extremely effective use of tint is to add texture to a dark blue background by tinting areas, making them lighter blue, to show raised portions. A surprisingly small amount of added white will result in definite and pleasing depth change for blue. This can be easily accomplished in most graphics programs with the emboss function if you have control of the highlight and shadow colors. Don’t forget to include some black in an embossed blue pattern to help define the location of the darkest blue.
Shading and Depth Position:
The opposite of tint is shade; a shade of a color is created by adding black to a pure color. Shading a color tends to move that color further away, in proportion to the amount of shading, regardless of whether it is a foreground color or a background color. A dark shade of red won’t move all the way back to the position of blue, but it will appear deeper than a bright red. The reason that shading creates this effect probably depends on our familiarity with shadowing to show roundness. Use shading with care; if an image element’s color is shaded darker than the shade of its local background, then the background color will predominate in determining its perceived depth position.
Color Quirks:
Red on yellow, with no black border between them, has an ambiguous depth position. It tends to look like the red is inside of the yellow area, near the middle ground. A black border restores the colors to their expected positions. Red on green can have the same trouble as red on yellow if there is no black border separating them. The controlling factor is the brightness of the green. A bright green will behave more like yellow, a dark green will behave more like blue.
Red on dark blue works without a black border. Light blues, or light tints of other colors, can produce a similar effect to yellow’s, so use a black border whenever there is any question. Magenta on black typically looks like a crisp, red object surrounded by a fuzzy blue halo. We don’t recommend using magenta unless you are seeking that kind of effect.
Creating Readable Text:
Black on white is the normal choice for text, but when using C3D™ Glasses, this combination is singularly difficult to read . The choice of font and size is important, too. We recommend a sans-serif font, like Arial, size 8 to 12 point, bold. We recommend any of the following color combinations for good readability:
