Liquid crystal displays (LCD's) use nematic liquid crystals. The molecular order in a nematic liquid crystal, which results from weak intermolecular forces, is easily disrupted. For this reason, the liquid crystals flow like a ordinary liquid. Because of the weakness of the intermolecular forces, the molecules in a nematic phase are easily realigned along new directions.
A liquid crystal display uses this ease of molecular reorientation to change areas of the display from light to dark or coloured, resulting in the patterns that you see in the display. The display consists of liquid crystals contained between glass plates whose interior surfaces are treated to align the molecules in a given direction. The space between the glass plates also contains polarizer sheets and transparent electrodes to reorient the molecules shown in figure 8-1. When the voltage to a set of electrodes in some area of the display is turned on, the molecules of the liquid crystal in that area reorient along a new direction. When this voltage is turned off, the molecules return to their original orientation.
Figure 8-1 The liquid crystal display
The purpose of the polarizer sheets is to make the change of molecular
orientation visible by using the ability of the liquid crystal
layer to change the plane of polarized light. Light
from the outside the display passes through the first polarizer, resulting in polarized light, which then passes through the liquid crystal layer. When the voltage to a set of electrodes in an area of the display is off, the liquid crystal layer in that area rotates the plane of the polarized light so that it can pass through the second polarizer. The display area appears bright. When the voltage is turned on, however, the plane of the polarized light is not rotated. In this case, the light can not pass through the second polarizer, and the area appears dark or coloured. The pattern on the display is created by turning sets of electrodes on and off shown in figure 8-2.
Figure 8-2 Typical twisted nematic LCD
The transmission of the LCD as a function of applied voltage is shown in figure 8-3. There is a threshold behaviour for most LCD's and no change in transmission occurs until a threshold voltage, Vth, is reached. Transmission then decreases as the voltage increases until saturation is reached. Threshold voltage is typical 1.5-2.5 volts, and saturation occurs at about 4-5 volts.
Figure 7-3 LCD transmission (brightness) as a function of applied voltage
The light transmission for IMPACT 256 LCD is measured to 2 %. The measurement is carried out with the help of a computer, laser, laser power meter and the LCD shown in figure 8-4. The measurement is made with and without the LCD. The LCD is connected in parallel with the computer screen, and one of the images used in the recording of holographic multi-stereogram is shown on the LCD.
Figure 8-4 Set-up for measurement of light transmission for IMPACT 256 LCD
Laser power without LCD : P = 24.21 mW.
Laser power with LCD : Pw = 0.51 mW.
Transmission: 
When the design stage is finished, we make a camera path where we get the positions of the viewpoints. From this camera path can see the target path, and we are able to see the object in different perspectives.
The light spots in front of the object give the image of the object
a natural look. This light spots can be moved or the intensity
can be adjusted so that the object gets bright, and we get the
desired effect for the picture.
Figure 8-5 Construction of Images used in the holographic proceeding
From the camera path it is possible to see the object in 50 different
perspectives. There is also possible to make 50 different images
of the object and make one file for each image. If we need more
than 50 different perspectives, we have to make more camera paths.
Then we can make as many pictures as desired of the object.
This files constructed in the AutoCAD program can be saved as bitmap files. The files that constructed are given the names < filenameXXX.bmp> where XXX gives the serial number of the image. In this thesis there are files from < name0000.bmp > to <name0069.bmp>, a total 70 different files.
Bildene er lagt ut pga for stor fil
Figure 8-6 An example on a sailboat seen from 3 different positions.
Figure 8-6 shows 3 different pictures of a sailboat. In an holographic multi-stereogram recording procedure with 70 different pictures, the first picture in the figure above would have the name Sail0000.bmp, the picture in the middle would have the name Sail0035.bmp and the picture to right on the figure would have the name Sail0069.bmp.
This bitmap files from the AutoCad program can be used directly in the ARIP control software program.
