Color Generating Techniques- Computer Graphics

There are two ways by which you can see some objects colorful, let’s say RED – the first method would be – if you wear RED Glasses on your eyes and second method would be you color the object RED. In other words – either you paint the source (eyes) or the destination (Object). We would call the electron beam coming out of the electron gun the Source and the phosphor screen it hit as the Destination. The following two methods are there available to produce colors.

• Beam Penetration Method – Where source is colored

• Shadow Mask Technique – Where the Destination is colored.

Beam Penetration Method

The BEAM Penetration method uses the Second method – that is the destination – screen – which has two phosphor layers – RED and GREEN, to be more specific – the inner layer is green and the outer layer is red. The color generated depends on how deep the beam of electrons penetrates into phosphor layers, for example – if the slow beam of electron penetrated only the RED layer then – the only RED color would be produced. A beam of the electron with moderate speed would penetrate both layers and would result in orange and yellow colors. Some of the key points about this method are –

• The obvious disadvantage of this method is – it can produce only four colors.

• The quality of the picture produced by this method is not good.
• This method is used only in random scan monitors,
• The acceleration of the beam is controlled by the voltage applied to the electron gun.

Shadow Mask Technique

This method colors the electron gun – the source and not the destination – the phosphor screen. This method uses three electron guns, colored – RED GREEN and BLUE. The electron guns are arranged in a triangular pattern. The electron guns pass through the hole on a mask and hit the phosphor screen. Why Mask is needed – the mask helps in stopping the dispersed color to reach the screen. The holes in the masks are aligned with pixels on the phosphor screen. If only BLUE colored gun is activated then only BLUE color is produced. The intensity of the light is changed to produce a wide range of colors. Some of the key features about this method

• This method is commonly used in Raster Scan Systems and in Color TVs
• Better quality of the picture is produced as compared to the beam penetration method.
• Gives a wide range of colors as compared to the beam penetration method.
• The dot that appears on the screen when you turn off the TV consists of three dots arranged in a triangular pattern.