Image Enhancement module

Description

The Image Enhancement module permanently applies image-enhancement features to images using enhancement algorithms or reference images.

Parameters

Name	Caption
Input Folder	Input folder
Input Channels	Input channels
Output Folder	Output folder
Output File Type	Output file type
Output File Options	Output file options
Overwrite Results	Overwrite existing results
Send Email	Email notification settings
Enhancement Method	Enhancement method
Trim	Tail-trimming percentage
Reference File	Reference file
Reference Layers	Reference layers

Parameter descriptions

Input Folder

The path and name of the folder containing valid GDB-supported images; typically, this is the output folder of the Data Ingest module.

Input Channels

The channels in the source image file to enhance.

The number of output channels must match the specified number of reference layers (segments).

Output Folder

The path of the folder to which to write the enhanced image files and quality-assurance (QA) data. The enhanced image files are output only in PCIDSK (.pix) format.

This parameter is mandatory.

Output File Type

The format of the output file.

For more information on the supported file formats, see GDB-supported file formats.

Output File Options

The options to apply when creating the output file or files. The available options are specific to the file format; in each case, the default of no options is allowed.

For more information on the options available for the output file type you specify, see GDB-supported file formats.

Overwrite Results

Select this check box to overwrite the existing output files, if any exist. If this check box is left clear, and an output file exists in the relevant folder, the status of the job displays a message informing you of the existence and name of the output file. The message is also written to the event log of the job.

Send Email

If necessary, you can set up CATALYST Enterprise to send an email notification on job start and job completion.

With this check box selected, an email message is sent to each address specified in the Email Addresses box after the job starts and on completion.

You can specify one or more addresses, and each must be separated by a comma or a semi-colon. The email address of the user currently logged in displays by default.

Enhancement Method

The type of enhancement to apply.

Available options are:

Histogram Equalization: produces an image in which gray-level values are distributed uniformly; each gray level in the transformed histogram occurs approximately the same number of times
Histogram Normalization: produces an image in which the histogram has a normal, or Gaussian, distribution. By default, the distribution has a mean of 127.5 and a standard deviation of 42.5, or 3.0 standard deviations per histogram tail. The number of standard deviations per tail can be specified using SDPT, and the mean will shift to the centre of a specified output gray-level range (OSTR).
Histogram Infrequency Brightening: produces an image in which the infrequently occurring gray-level values in the input image are mapped to the high end of the gray-level spectrum
Adaptive Enhancement: produces an enhanced image based on the median value of the image
Reference Image: uses the image specified for the Reference File parameter to extract a lookup table (LUT) to enhance the input images
Existing LUT: uses the existing LUT segments in the source images
Existing Reference LUT: uses an existing reference file with LUT segments stored to enhance the input images

When the value of the Reference File parameter is a valid reference file, this parameter is ignored; otherwise, this parameter is mandatory.

Trim

Images can contain pixel values that fall far outside the bulk of the others in the range. These values, referred to as "outliers", can skew the histogram, which can reduce the effectiveness of the color balancing. Trim removes the upper and lower percent of the range, eliminating such outliers. Acceptable trim values are 0 to 100 percent. Trimming up to five percent of the range is effective; however, two percent is recommended for most data sets.

Reference File

The file name of the reference file.

You use this parameter only when you select either Reference Image or Existing Reference LUT in the Enhancement Method list.

When you select Reference Image, the reference file you specify will be used to generate LUTs to apply to the source image for enhancement. When you select Existing Reference LUT, the reference file you specify will be a file that contains the LUT segments that will be applied to the source image for enhancement.

Reference Layers

The layer or layers in the reference file to use as the basis for the enhancement.

You use this parameter only when you select either Reference Image or Existing Reference LUT in the Enhancement Method list.

When you select Reference Image, the reference layers you specify are the channels in the reference file you want to match. The number of input channels must match the specified number of reference channels. When you select Existing Reference LUT, the reference layers you specify are the LUT segments in the reference file that will be applied to the input channels.

Details

General job details

Preprocessing requirements

Before running this module, the following requirements must be met to ensure the job processes successfully and produces accurate results:

With raw satellite scenes, use the Data Ingest module to convert scenes to PCIDSK format

Module details

The Image Enhancement module finds valid images to enhance, and then creates and runs a child job for each image accordingly.

Each child job first calculates a LUT, using either the standard enhancement functions (histogram equalization, histogram normalization, infrequency brightening, or adaptive enhancement), or by matching the source image to a reference image. It then applies the LUT to the corresponding raster channels and generates an enhanced image. All channels in the enhanced images (output) are 8-bit unsigned channels.

A temporary link file is written to the output folder for QA purposes. This file links to the source image file and stores the LUT segments generated during processing. It has the same name as the source file, but is in PCIDSK format.

Job results

For each valid image file in the input-scenes folder, the module creates and writes two output files to the specified output folder after processing:

An enhanced image file, with the same file name as the source image, but in PCIDSK format
A temporary link file in PIX format that links to the source image file and stores LUT segments

Note: All channels in the output enhanced images are 8-bit unsigned channels.