Color Management in 3D Visualization
Of course, when visualizing 3D content, you want the colors to be displayed just as correctly as in two dimensions. However, because the INFITEC method is based on the fact that the intensity distribution over the wavelengths on the left and right sides is different, there is always the possibility that the colors in the left and right images do not match. This used to be even more pronounced with the first generation of INFITEC filters because only three wavelength bands were used per side. Therefore, in the early days of 3D projection using the INFITEC method, it was often necessary to insert a special color processor between the image source and the projectors. With the introduction of the Excellence® filters, it has become much easier, because the left and right images already match much better in terms of color. Special color processors no longer have to be used; the remaining differences between the two images can be corrected using the color settings available on each projector – if this is necessary at all. At the same time, the color balance already built into the filter makes the projected image brighter. The reason for this is explained below.
How do the Excellence® filters do this? The human eye has three different types of color vision sensory cells (cones), one each for red, green and blue. A green color sensation is triggered, for example, when the eye receives light wavelengths in a certain range that is different from the ranges for red and blue color sensations. Whereas in the past each of these areas was divided into two bands, the Excellence® technique now uses three bands per color. Let’s take green again as an example, where the following is just as applicable to red and blue. Of the three bands that divide the “green” wavelength range, the two outer ones are fed to the left eye and the inner one to the right eye. The two outer bands are now selected so that the color impression conveyed by the transmitted light is exactly the same as that produced by the middle passband. The fact that this is possible has been known for a long time and is called metamerism. The outer transmission bands of green are adjacent to one of the outer transmission bands of blue (on the short wavelength side) and red (on the long wavelength side) and are combined with these. Thus the (imaginary) nine bands merge into seven, four of them for the left and three for the right image. The spectral widths of these bands are adapted to the light source in a complex simulation process in such a way that the perceived colors on the left and right match as closely as possible.
Of course, this is not possible for every single projector (at least not at an affordable price), so that there are usually still slight color differences left, which can be more or less annoying depending on the application. However, these can be compensated with the adjustment possibilities that every modern digital projector offers. Professional projectors have additional and more comfortable settings than home projectors. In the professional sector, if the color rendering requirement is very high, the color adjustment can be quite complex. For this one needs a spectroradiometer, with which one measures the intensity over the wavelength of the radiation of the projector concerned both without INFITEC filter and also with. These spectra are then calculated with each other and with data of the desired color space; the results can be entered directly into the settings menu of professional projectors. This is usually not possible with consumer devices. But on the other hand, a visual adjustment based on special test images is usually sufficient. In the case of high demands, a spectroradiometer is used again, but in most cases several iterations have to be carried out until all colors are correct. It has to be considered that each color correction inevitably costs brightness, as the projectors are usually designed to deliver the maximum luminous flux without corrections. If, for example, the image is slightly greenish, one cannot make red and blue brighter, but must darken green. Frequently, a small color difference between the left and the right image can also be tolerated, so that a compromise between color fidelity and brightness can be made.