Final answer:
The image on an LCD screen is produced by a backlight illuminating pixels composed of sub-pixels with red, blue, and green filters, which are controlled independently. Adjusting the voltage applied to these pixels changes the picture contrast.
Step-by-step explanation:
The image presented on an LCD screen is a representation of the electronic signal conducted by the liquid crystals in the pixels. In flat-screen LCD televisions, a large light at the back of the TV illuminates the screen through millions of tiny units called pixels. Each pixel has three sub-pixels with red, blue, or green filters, and these are each controlled independently to create the full spectrum of colors on the screen.
When the voltage across a liquid crystal is switched off, the crystal allows light to pass through and reach the front screen through the filter. By varying the strength of the voltage applied to the liquid crystal, you can change the picture contrast.