Planar
From Wikipedia, the free encyclopedia
- For other uses, see Planar graph.
- For the corporation, see Planar Systems.
- For the photographic lens, see Zeiss Planar.
Something is called planar if it is made up of flat planes, or pertaining to planes. A graph is called planar if it can be drawn in the plane without any edge intersections; see planar graph.
In the context of computer graphics, Planar is method of representing pixel information with several bitplanes. There are also cases where byteplanes have been used. Each individual bit in a bitplane is related to a single pixel on the screen. Unlike Chunky, Highcolour or Truecolour graphics, the data for an individual pixel isn't in one specific location in RAM, but spread across the bitplanes that make up the display.
For example, on a Chunky display, each byte will represent one pixel. So, if colour zero is black, colour one is blue, and colour two is green, a byte of chunky pixel data would look like this:
00000000 = Black pixel
00000001 = Blue pixel
00000010 = Green pixel
Whereas planar data would look like this (assuming the use of 2 bitplanes, providing for a 4 color display):
Plane 0, Byte 0: 00000000 = 8 black pixels
Plane 1, Byte 0: 00000000
Plane 0, Byte 0: 10000000 = 1 blue pixel, 2 black pixels, 1 green pixel, 4 black pixels
Plane 1, Byte 0: 00010000
Planar graphics were used a lot in the 80s and early 90s because displays tended to only be able to show fewer than 256 colours. Chunky displays always represent one pixel within a contigous grouping of bits. And usually have 1 byte or more per pixel, even with a colour depth not a multiple 8 bits (sometimes going as far as storing a 24 bit image in 32 bit chunks). This wastes RAM in cases where fewer bits are needed than are provided. If you only need to display 8 colours, you can use 3 bitplanes, and each pixel only has 3 bits assigned to it instead of 8 (reducing memory and bandwidth requirements by 62.5%).
