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| Start page | Håkan Lans | Color graphics | ||
The color graphic in a computer
How the graphic card is built?:
There are three components which are important on a graphic
card: the memory, the graphic processor and the DAC.
DAC (Digital-to-Analog Converter) is the unit that convert the digital signal
from the graphic memory to analogous signals which the screen can construe. The
component plies constantly data, about 80 times/sec. The faster DAC you have,
the more signals per second does the unit sent to the screen. If the screen is a
LCD-monitor (a special flat screen), you doesn't need DAC. A screen like that is
namely digital, i.e. it can construe signals that comes directly from the graphic
card. A LCD-screen is located in laptops.
The graphic processor calculates all the statements which it got
by the main processor. Then the information been sent forward to the graphic
memory. The processor's task is to relieve the pressure on the main processor,
so it doesn't need to work so much with the graphic.
The memory is the link between the graphic processor and DAC. In the
memory all data been temporary saved as ones and zeros (binaries numbers). The
memory must be very fast, as the information comes from
the graphic processor all time that got to be saved. Because that the memory always is
occupied. There are plenty of memory types among of VRAM (Video RAM) and SGRAM (Synchronous
Graphic RAM).
How the process send information to the screen?
The main process send a instruction to the graphic card what will be visible.
The graphic process work and calculate the information and send it forward to the graphic memory.
In the memory the data will be saved a couple of milliseconds.
Now the DAC begin to work. The component transforms the digital signal to analogous.
Signals been sent from the graphic card to the screen.
How a screen work (not LCD):
Electrons been sent from the electron canons (the screen's back) to the surface of glass.
On the back of the glass a layer of phosphorus is located.
When the electrons hit the glass of phosphorus, do the electrons been showed some milliseconds.
There is a plate of metal with small holes in between the layer of phosphorus and the glass.
The holes make the electrons to be sent to a more exact place, i.e. the picture became clear.
Why does the screen flicker??:
That the screen flicker so much that you get pain in your eyes can depend on two things: the screen or the graphic card. The flicker can depend on that the electrons in the screen fade out after a very short time. If it doesn't has been sent new electrons from the electron canons, it will be a vacant space, i.e. flicker. It can also be that the electron canons can't get necessary with data from the graphic card. Then the DAC maybe is too slowly.