There are different modifications of the tube technology that are used for the digital and analogues screen projectors. Actually, the most part of projectors are able to output an excellent quality picture, though they are forced to work with analogues sources, which have a lower quality.
Some projectors receive an interlaced input signal, which is an analogue to the one used for TV broadcasting. In this case, the image is formed in two passes. To apply this tube technology, the projector's electronics must have the ability to adapt the signal before putting it to the projecting system. Another approach is to create thirty cadres per second from received twenty four cadres. This responsibility is delegated to the digital processing system that increased the clearness of the image. Producers of the systems use their own chips or expensive solutions from the side companies. One of the most important high quality solutions is a chip with the support of the DCDi technology by the Faroudja Company. This chip or its analogue must be integrated to any projector. Therefore, it has a strong competition that takes a larger part of the market and has identical characteristics - this is the Zoran chip.
The digital solutions, applied to the projectors, must work in a combination with analogue solutions. This principle is implemented in the family of the CRT screen projectors. These devices are provided with a CRT tube, which forms an image and retranslates it to the screen.
The tube technology is the oldest approach to the image forming. In this case, the picture is created with CRT tubes. Nevertheless, the principles of the tube technology for projectors are rather different than the approach, used for home TV.
Such projectors have three CRT tubes at once. Each tube is responsible for one main color - red, green or blue - which are forming the image. It is enough to provide three basic colors to create a full quality image of any complexity. The required color is formed by a special filter that is placed behind the tube. This principle is common for all the RGB systems.
The color stream, combined of three main colors, passes through the system of lenses and focuses at the screen with the full color picture. Such projectors have an excellent color rendering and real flat high brightness. This result can be achieved, since the tube technology was developed for many years. The CRT projectors are able to pass the black color perfectly in difference with other types of projectors.
The main disadvantage of the CRT projector system is its big size and weight. Each tube has a diameter higher than ten sm and it requires some strong cooling. In addition, a high quality image is formed due to the reduction of three pictures at one screen. This procedure is complicated for the adjustment and it does not allow to move the projector fast, when the adjustment is completed. These projectors have a too high price for today. However, they provide a very high quality; thus, a user has to choose the model according to his preferences. At the same time, these projectors are good, when they need to be set up once and forever and no one is going to move them often.