USGS MIPS Glossary

USGS MIPS Glossary

Digital Number

A Digital Number or DN is the value stored within a pixel or cell of an image. Typically, the DN of the pixel represents the amount of light reflected back to the satellite/sensor. However, this is dependent upon the type of data stored in the image. For example, here is a list of some types of images and what the DN would represent:

DEM, Elevation

Sonar, Strength of returned soundwave

Radar, Strength of returned microwave

Thermal Infrared, Heat emission

Regardless of what the DN represents, they are treated in the same way when displayed. That is, a DN of 0 will appear as black, of 127 will appear gray, and of 255 will appear white. The example image given below shows an image in which DN values progress from 0 to 255 from left to right.

[Example Image]

Histogram

A histogram is a frequency count of the number of occurences for each DN value in an image.

History

A history file is a text file associated with a particular MIPS image which has the same name as the image but with a ".hst" extension. This file contains a listing of all the processing in which its corresponding image has gone through. The format of the history file includes the program name, files and parameter selections for this program followed by a line of dashes; afterwards the history for the next program follows.

Image

An image is a two-dimensional array of pixels where the horizontal rows of pixels are called lines and the vertical columns are called samples. The pixel at the top-left corner of an image is said to be coordinate (Line 1, Sample 1) while the pixel at the bottom-right corner is said to be coordinate (Number of Lines, Number of Samples). A MIPS image file is identified by having the image name followd by ".img".

Labels

A labels file is a text file associated with a particular MIPS image which has the same name as the image but with a ".lbl" extension. This file can contain either image, sonar, navigation, projection, transformation, vector or mosaic information for its corresponding image. The number of lines and samples and image type are examples of the kind of information that can be found under image labels.

Navigation

A navigation file is a text file associated with a particular MIPS image which has the same name as the image but with a ".nav" extension. Information such as date, time, latitude, longitude, roll, pitch, heading, velocity, altitude, depth and left/right slant range distances are recorded for every line of data in the sonar image.

Pixel

A pixel is the smallest element that makes up an image.

Print file

A print file is a text file created by a MIPS program after processing an image. This file contains information such as: program name, execution date and time, input and output file names and sizes, parameter selections, program specific information and other information such as actual CPU time used and page faults.

Stretch

A stretch is a mapping of one or more DNs from their original values to new values. When an image is said to be "stretched", all the DNs in the image could have had been remapped to new DN values. The following stretch, "0;0 100;0 255;255", maps all the dns in an image between 0 and 100 to zero; while mapping dns between 101 and 255 between 0 and 255.

Stretch file

A stretch file is a text file associated with a particular MIPS image which has the same name as the image but with a ".str" extension. With the use a program, any of the stretches found in this file can be applied to the image.

Stretch pairs

Stretch pairs are pairs of numbers(DNs) seperated by a semicolon where the first number will be mapped to the second. The following stretch pair, "5;100", maps every pixel in a image with a DN value of 5 to a pixel with a DN value of 100.

8-bit

An 8-bit image is an image created using 8 bits(a byte) for every pixel or DN value at each line/sample coordinate. Using eight bits per pixel allows whole numbers between 0 and 255 to be used as DN values.

16-bit

A 16-bit image is an image created using 16 bits(two bytes) for every pixel or DN value at each line/sample coordinate. Using sixteen bits per pixel allows whole numbers between -327687 and 32767 to be used as DN values.

32-bit

A 32-bit image is an image created using 32 bits(four bytes) for every pixel or DN value at each line/sample coordinate. Using thirty-two bits per pixel, allows real numbers between the minimum and maximum floating point numbers allowed on the current configured system, to be used as DN values.

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Last Modified: Thu Oct 31 15:08:24 MST 2002