Raster Type Data

Raster data consists of a series of black and white dots (or called pixels when displayed on a computer screen). All data that the scanner captures and converts into these digital dots is then stored into various raster formats. These formats each have a different algorithm as to how they are written to a file and compressed. When a raster file is first created, it accounts for every pixel (or dot) space on the drawing that is scanned. This takes a tremendous amount of storage space when you think that the initial raster file (termed uncompressed) accounts for the entire surface of the drawing. The initial scanned raster image is then compressed to minimize the storage space allowing greater storage capacity on the computer drive where they are stored. When dealing with black and white (monochromatic) scanning there are two types of raster types:

Binary (Linework)
Continuous Tone (Greyscale)
Binary raster (referred to as a "0" or a "1" by the computer) scanned files are typically engineering drawings or linework based art that shows up as either black or white in the image.

Example = Drawing.ras

Continuous tone (referred to as a range of progressive gray values from "0 to 255") scanned files are typically photographs, artwork such as air brush media or screened media that shows up in tonal grays ranging from pure white to pure black expressed in 256 values versus only the two ("0" or "1") that binary displays.


Example = Drawing.cot

Both binary and continuous tone are scanned and displayed using the term "resolution". Resolution is the number of dots per inch (dpi) used to scan and store the drawing of image.


Example = "E" sized drawing scanned at 200dpi.

Data Compression

Raster data is normally compressed to optimize the storage space on your computer drive. When a raster file is saved in your software application, you have a variety of compression (algorithm) formats to choose from.

Example = Drawing.ct4

These fall under two categories as well. They are lossless and lossy. Lossless compression litterally squeezes the digital raster file into a smaller file size without any loss of data. Lossy squeezes the digital raster file even more decimating the image so that it can radically compress it into a far smaller file size.

Example = Drawing.tif (Lossless)

Example = Drawing.jpg (Lossy)

VECTOR TYPE DATA

Vector data is normally created from CAD (computer aided design) Programs. It is one of the most efficient forms of data storage because it only requires a minimum amount of data points to describe an image. Because of this compression is normally not used when storing these type of image files on disk.

Example = X 1, Y 4………X 1, Y 14 (This might be all the information needed to describe (1) vector line in an engineering CAD drawing).