USGS MIPS Stretch Documentation

USGS MIPS Stretch Documentation

This program is one of the X Windows applications that can be executed under the Applications pull-down menu in VISTA. STRETCH allows a user to interactively contrast stretch an image or composite of images loaded into VISTA.

Options

This pull-down menu allows the user to select options used in stretching an image. There are currently two modes in which an image can be stretched, these are the automatic and manual stretching modes. For more information on any of these two stretching modes, select the apropriate link below.

Automatic Stretch
Manual Stretch

Along with selecting one of these options, the user may also define minimum and maximum dn ranges to be used in the stretch process.

Min/Max Dn Range

This dialog box provides the user with choices in selecting other minimum and maximum DN ranges to be used in the mapping of DNs. These options allow the user to define min and max values for the image or images instead of using the default one and ninety nine percent values automatically selected from the images histograms . The min and max values are used determine what DN ranges are actually stretched. All DN values less than the MIN or greater than the MAX values are assigned black and white, respectively.

Automatic Stretch Option

This option allows the user to automatically stretch an image. Automatically stretching an image, allows the user to interactively stretch the entire image at once.

Method

This selection box allows the user to select the method to use in the stretching of the image or images.

Linear

A Linear stretch is used to map DNs in the min/max dn range between 0 and 255.

Width
This selects the size of the window used to obtain histogram information from the image. Moving the sliding box left and right decreases and increases the window size around the middle DN, respectively.

Middle DN
This selects a DN value used as the middle DN value in which the window is centered around. Moving the sliding box left and right allows the user to manually select this value. By default, the middle DN is automatically calculated from the histogram.
Binary

A Binary stretch allows the user to apply a stretch that maps DNs inside a DN window to 255 while mapping everything else outside this window to 0, thus resembling a binary pattern when looking at a plot of the stretch against the histogram.

Width
This selects the size of the DN window. Moving the sliding box left and right decreases and increases this window centered around the middle dn, respectively.

Middle DN
This selects a DN value used as the middle DN value in which the window is centered around. Moving the sliding box left and right allows the user to manually select this value. By default, the middle DN is automatically calculated from the histogram.
Binary II

A Binary II stretch is a combination of a Linear and Binary stretch. This stretch allows the user to apply a stretch that maps DNs inside a DN window to 255 while mapping everything else outside this window to 0 and 255.

Width
This selects the size of the DN window. Moving the sliding box left and right decreases and increases this window centered around the middle dn, respectively. Note that this window moves along the linear stretch of the image.

Middle DN
This selects a DN value used as the middle DN value in which the window is centered around. Moving the sliding box left and right allows the user to manually select this value. By default, the middle DN is automatically calculated from the histogram.
Sine

A Sine stretch allows the user to apply a stretch that maps DN values back and forth between 0 and 255, in a sine wave like manner. This stretch was developed to enhance subtle brightness/color differences in an image for dark and bright areas simultaneously.

Number of Cycles
This selects the number of cycles. Moving the sliding box left and right decreases and increases the number of cycles, respectively.

Base DN
This selects the starting DN where the Sine stretch will begin. Moving the sliding box left and right selects lower and higher DN values, respectively.
Threshold

A Threshold stretch is used to emphasize a range of DNs by turning them white and everything else black on the screen. This option is identical to the method used to select the min and max values for the automatic linear stretch, except instead of mapping them to 0 and 255, respectively, the DN values inside the min and max range are all mapped to 255 and everything else to 0.

Threshold DN
This selects the starting DN value used as a threshold between stretching to black and white. All the dns below this value will be black while all the dns above this value will be white. Moving the sliding box left and right allows the user to manually select DN values lower or higher than the threshold automatically calculated.

Red, Green and Blue Channels

These radio buttons allow the user to toggle the stretching for the respective channels on and off as desired. Toggling channels allows the user to interactively stretch one channel at a time.

Apply

Selecting this button allows Stretch to apply the currently selected stretch to the image.

Manual Stretch Option

This option allows the user to stretch an image or images specifically on a DN by DN basis.

Mono/Red, Green and Blue Stretch

The three input boxes labeled "Mono/Red Stretch", "Green Stretch" and "Blue Stretch" are used to enter stretch pairs to apply to the image or images. If only one image is loaded into Vista, the "Mono/Red Stretch" labeled box will be the only available option whereas loading three images enables all three options. Entering the stretch pair "50;130" for an image allows Stretch to map the dns in the image starting at 50 to a value of 130. Note that elements of each stretch pair must be separated by a semicolon ';', and the pairs must be in increasing numeric order with respect to the first input elements. Also, each stretch pair must be separated by one or more blanks and the order is assumed to be 'input;output'.

Apply

Selecting this button allows Stretch to apply the currently selected stretch to the image or images.

Exiting Stretch

Selecting the "Exit" item from the file pull-down menu will cause this program to terminate.