Posted: January 16, 2014 in Computer Graphics
Color CRT Monitors - A color CRT monitor displays color picture by using a combination of phosphors that emit different colored light.
- By combining the emitted light a range of colors can be generated.
- Two basic methods for producing color
displays are:
1. Beam Penetration Method - Random scan monitors use the beam penetration method for displaying color picture.
- In this, the inside of CRT screen is coated two layers of phosphor namely red and green.
- A beam of slow electrons excites only the outer red layer, while a beam of fast electrons penetrates red layer and excites the inner green layer.
- At intermediate beam speeds, combinations of red and green light are emitted to show
two additional colors- orange and yellow.
Advantages Disadvantages - Quality of images are not good as comparatable with other methods
- Four colors are allowed only
2. Shadow Mask Method - Raster scan system are use shadow mask methods to produce a much more range
of colors than beam penetration method.
- In this, CRT has three phosphor color dots.
- One phosphor dot emits a red light, second emits a green light and third emits a blue light.
- This type of CRT has three electrons guns and a shadow mask grid as shown in figure below:
- In this figure, three electrons beams are deflected and focused as a group onto the shadow mask which contains a series of holes.
- When three beams pass through a hole in shadow mask they activate dot triangle as shown in figure below:
- The colors we can see depend on the amount of excitation of red, green and blue phosphor.
- A white area is a result of all three dots with equal intensity while yellow is produced with green and red dots and so on.
Advantages - Produce realistic images
- Also produced different colors and shadows scenes.
Disadvantages - low resolution
- expensive
- electron beam
directed to whole screen
Full Color System Color CRTs in graphics systems are designed as RGB monitors. These monitors use shadow mask method and take the intensity level for each gun. A RGB color system with 34 bits of storage per pixel is known as full color system or true color system. Difference between Beam Penetration and Shadow Mask method.
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| Beam Penetration method
| Shadow Mask method
| | Where Used
| It is used with Random Scan System to display color.
| It is Used With Raster Scan System to display color.
| | Colors
| It can displays Only four colors i.e. Red , Green, Orange and Yellow.
| it can display Millions of colors.
| | Color Dependency
| Less colors are available because the colors in Beam Penetration depends on the speed of the electron beam.
| Millions of colors are available because the colors in Shadow Mask depends on the type of the ray.
| | Cost
| It is Less Expensive as compared to Shadow Mask.
| It is More Expensive than other methods.
| | Picture Quality
| Quality of picture is not so good i.e. Poor with Beam Penetration Method.
| Shadow Mask gives realism in picture with shadow effect and millions of color.
| | Resolution
| It gives High Resolution.
| It gives Low Resolution.
| | Criteria
| In Beam Penetration method, Color display depends on how far electron excites outer Red layer and then Green layer.
| In Shadow Mask Method, there are no such criteria for producing colors. It is used in computers, in color TV etc.
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What are the advantages of shadow mask method over it?
Advantages of Shadow Masks in CRT Monitors
A more realistic image is possible with shadow masking because shadow masks allow for millions of colors to be generated on the monitor. In the past, producing shadow masks at scale for production was potentially cost prohibitive.
What is shadow masking method?
Shadow Mask Method :
Shadow Mask Method is the method which is used in raster scan system which includes color TVs. In this the pixel is made up of three -colors. So due to three colors it uses three electron guns one for producing each color. The colors are red, green and blue.
What are two disadvantages of CRT monitors compared to flat panel?
CRT monitors emit heat and consume more energy than other monitors like LCD, LED. They do not work with full potential while playing with graphics and resolutions. They are less attractive while compared to LCD and LED monitors. They produce more magnetic fields, therefore, can damage other magnetic devices.
What are the two popular approaches for producing color displays with a CRT?
The two basic techniques for producing colour displays with a CRT are the Beam-penetration method and the Shadow-mask method.
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