Zoher and Company stays up to date with technological advances and constantly strives to improve our products. To understand properly the quality and care taken into manufacturing our cinema projection screens you must understand a few basic scientific and technical terms used to describe surface qualities and performance.
Moire:
A word used to describe visible distortions in the uniformity of the screen surface; or the distortions in picture clarity. The term comes from the French word "moirer" (to water) and is used to express a rippled, water-like look.
Colorimetry:
A technique by which an unknown colour is evaluated in terms of standard colours. This is mostly carried out visually although there are other available technologies such as photoelectric or indirectly by spectrophotometry to evaluate the screen's performance in terms of contrast and colour testing. The customer has no choice but to take the manufacturers word in such instances as the testing equipment is very expensive and not available to everybody.
Polyvinyl Chloride (PVC)
This is a widely used plastic in a huge variety of applications. The cinema screens commonly used today are made from the softer version by adding the required plasticizers. Normally referred to as vinyl screens, they are joined at the seams by welding creating linear joints. All good screens have joints that are invisible under normal projection conditions. The silver screen used for 3 dimensional screens can have visible seams if used for a wider viewing area.
Technical Terms
1. Uniformity
Uniformity refers to not only how the screen displays an image, but also how well the projector is projecting the image. Traditionally, screen measurements are made by pointing a light metering device at the centre of the screen. This is good information, but it only tells how bright a screen’s center will appear from different viewing angles ranging from 0 to 180 degrees. Information and images on the edges may lose light.
Projection screens have very uniform coatings, but the projectors may not laminate perfectly uniform. Depending on the type of projector, the length of the lens, the distance the projector is to the screen, and the screen itself will ultimately determine image quality.
Project manufacturers also do a type of light reading of their projector called lumens. The American National Standards Institute (ANSI) has created a way to measure brightness of an image. The image is divided into 9 rectangles each of which measures 1/3 of the screen width. A brightness reading is taken at the center of each rectangle and then the average of the nine reading in lux (lux = lumen/ square meter) shall be multiplied by the number of square meters of the image at the plane of the meter reading. The result is the light output of the projector in lumens.
CRT projectors are more commonly non-uniform, with limitations from the light emitted from each of their RGB (red, green and blue) guns. The light emitted from the center of each of these guns slowly dimmer at the circumference edge. This is partial to blame for what is commonly known as hotspots. Hotspots can be avoided by choosing the right screen, projector, distance of the projectors of the screen, and projector settings.
Optical coating may also help in creating light uniformity. Optical coating scatters light rays producing a more inform image.
2. Resolution
Resolution is defined as “the fineness of detail that can be distinguished in an image, as on television.” There are two major projectors, which either deal with bandwidth (CRT projectors) or with pixels (LCD, DLP, D- ILA projector).
3. Pixels
When we look at an image we are actually seeing the end product of the visual chain. Image data is combined from software and hardware, and then electrically divided up into an exact number of bits. Projector converts the bits into beams of light, which are called pixels. one pixel is the smallest image forming unit of video display.
If a projector has a resolution of 640 by 480, we can then calculate it will cast an image with 307,200 pixels. Pixels are organized on horizontally and vertically, every image is created by completely filling in or not filling in each pixel with color. A good way to compare an image made by pixels is to a large puzzle with tiny pieces.
Advantages - Digital signal does not lose original composite regardless of how many copies - Pixels are assigned specific destinations, which is electronically placed in a fraction of a second
4. Bandwidth
CRT projectors index how many bits of information the projector can process every second. Bandwidth is measured in units expressed in kilo Hertz. A projector scanning at 100 kHz is scanning 100,000 cycles/ second. The larger the kilo Hertz, the wider the bandwidth and the faster the cycles per second. The image resolution will ultimately depend on what we can perceive visually, regardless of the bandwidth size.
5. Contrast
Contrast is just as important as uniformity and resolution. Contrast simply is the difference between light and dark areas. Contrast depends on ratio between maximum and minimum light level within any image. It is calculated by dividing the peak white levels by the light level at the dark part of the picture. Measurements are taken at the peak white and an area of black near the white. Blacks are never really true black in color black, black is absent of light. If you turned on the lights during a presentation, the screen once filled with vibrant colors and contrasts are now faded and dull.
Zoher and Company has introduced our grey back projection material for superior picture contrast for rear projection.
6. Half Gain Viewing Angle
Half gain is the standard that the projection screen industry uses to measure the brightness performance of a projection screen when the viewer is observing the screen from an extreme angle or “off to the side”.
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