Bit-Mapped Graphics #1

 

A  bit mapped frame buffer stores data about every pixel in an image.

 

The frame buffer is the VRAM.

 

A bit plane is a binary digit containing tone, intensity or colour information about a pixel.

 

If we had a display of 640 x 480 pixels then

				640
	480

 

 

 

 

 

 

 

 

There is a total of 640 x 480 = 307 200 pixels.

If this is monochrome, black and white, we only need to know if the pixel is ON or OFF (1 or 0).

This is stored in a bit (Binary Digit) and we need one bit per pixel. So, we need 307 200 bits.

 

307 200 bits =          307 200 ¸ 8 bytes

                        =          307 200 ¸ (8x1024) kilobytes

                        =          38 kilobytes

 

 

 

Shades of grey can be achieved by having more bits per pixel.

 

            2 bits give four shades

            4 bits give sixteen shades

            6 bits give sixty four shades

 

 

Memory needed is

 

            2 x 38 = 76 kilobytes

            4 x 38 = 152 kilobytes

            6 x 38 = 228 kilobytes