Input Resolution
Scanner input resolution is described as SPI, which stands for Samples per Inch. The term "sample" refers to sampling the continuous tone image being scanned into pixels (picture elements.) Once an image is scanned the resolution is described as PPI, Pixels per Inch.
File Resolution
A digital image's resolution is described in Pixel per Inch or Pixels per Centimeter. It is important to understand that an image has total pixel dimensions as well as PPI or PPC resolution. An image that is 2 by 2 inches at 150 pixels per inch has a total pixel dimension of 300 by 300 pixels.for a total pixel count of 90,000. when the PPI resolution of an image is increased, the total pixel dimensions both increase, greatly increasing the file size.
A one inch square image at two PPI and four PPI.
You can see that doubling the image's resolution quadruples the number of pixels and the uncompressed size of the file.
Output Resolution—DPI, LPI, EPI, and EIEIO
DPI
Again, most people use DPI and PPI to refer to any resolution attribute.
In ink-jet printing, DPI really refers to the "dots" that an ink-jet
printer puts on paper. In halftone printing, DPI refers to the small printers
dots that make up the larger halftone dots in the line screen. These smaller
dots which make up the larger halftone dots are also known as recorder elements—RELS.
LPI
LPI, lines per inch, refers to the halftone screen resolution. Generally,
ink-jet printing does not encompass halftone printing. When working with
halftone screen resolution it is important to understand that the combination
of printer dot resolution (RELS) and halftone line resolution (LPI) control
the number of tones that can be printed.
EPI
EPI, elements per inch, refers to the printer dot elements (RELS) that make
up the halftone dots. This resolution is usually found in laser printers
and imagesetters—high-end, pre-press printers. EPI is not a factor
in ink-jet printing.
EIEIO
For detailed information on EIEIO follow this link. EIEIO
