reduce

This program reduces a cube to a given proportion of the original or to specific pixel dimensions.

The reduction method options include either averaging the pixels (AVERAGE) or selecting the closest pixel at the window center (NEAREST) when generating a sub-sampled cube. More information is included under the Parameter Group headings.

For Level1:

• All keywords in the input file label are propagated to the output file
• An AlphaCube group with the original size is created in the output cube labels
• Coordinates returned in qview are accurate if SPICE kernels are present in the labels

For Level2 or Mosaic:

• The Scale and PixelResolution are recomputed if SSCALE and LSCALE are equal
• The Mapping Group is removed if SSCALE and LSCALE are not equal
• Coordinates are returned in qview only if the Mapping group was propagated
• Use the same value for SSCALE and LSCALE if the reduced cubes will be mosaicked together

Use the ONS and ONL parameters with caution because the scaling factor for the samples and lines may be different in the output cube. Within this application, special pixels are considered invalid and will be replaced depending on the settings for VALIDPER and VPER_REPLACE parameters.

Description

Use this parameter to select the filename. All bands within the file will be scaled down.

Type	cube
File Mode	input
Filter	*.cub

Description

This file will contain the results of the reduced cube. The output cube may not have all the keywords propagated to the output file depending on the reduction method chosen, and the type of input file.

Type	cube
File Mode	output
Filter	*.cub

Description

Select the algorithm to use to reduce the image. The AVERAGE option will compute the output value by averaging the input pixels. The NEAREST option will assign the input pixel that is closest to the center of the window being analyzed as the output value.

Type	string
Default	AVERAGE
Option List:	Option Brief Description AVERAGE Average surrounding pixels Use pixel averaging to reduce the image. NEAREST Nearest-Neighbor Use the nearest-neighbor algorithm to reduce the image.

Description

Select between reducing the image to a proportion of the original (use a scaling factor inverse) or to specific pixel dimensions (define total number of pixels).

Type	string
Default	SCALE
Option List:	Option Brief Description SCALE Reduce by a scaling factor inverse Reduces the input image by a scaling factor inverse. The scaling factor inverse must be specified in the SSCALE and LSCALE parameters, respectively. Exclusions ONS ONL Inclusions SSCALE LSCALE TOTAL Reduce to specified pixel dimensions (samples, lines) Reduces the input image to a total number of pixels. The number of pixels in the output image must be specified in the ONS and ONL parameters, respectively. Exclusions SSCALE LSCALE Inclusions ONS ONL

Description

This is the scaling factor inverse for the sample direction. For example, SSCALE=4 will reduce the number of samples by 1/4th.

Type	double
Default	1.0
Minimum	1.0 (inclusive)

Description

This is the scaling factor inverse for the line direction. For example, LSCALE=4 will reduce the number of lines by 1/4th.

Type	double
Default	1.0
Minimum	1.0 (inclusive)

Description

The number of samples desired in the output cube. This value must be less than or equal to the number of samples in the input image.

Type	integer
Minimum	1 (inclusive)

Description

The number of lines desired in the output cube. This value must be less than or equal to the number of lines in the input image.

Type	integer
Minimum	1 (inclusive)

Description

This parameter specifies what percentage of the pixels need to be valid (non-special pixels) to determine the output value based on the reduction method chosen. For example, scaling down by a factor of two results in a 2x2 window (four pixels) being reduced to one pixel. If VALIDPER is set to 50, then at least two of the four pixels (50%) must be valid. If this criterion is met, then the result is derived using the valid input pixels based on the chosen algorithm. Otherwise, the output pixel is assigned a NULL value by default or the closest pixel if "NEAREST" is chosen for VPER_REPLACE.

Type	double
Default	50

Description

This parameter specifies the method to use when the value specified for VALIDPER is not met. The resultant pixel will be filled based on whether NULL or NEAREST is chosen for this parameter. The default is to replace with a NULL value if nothing is defined by the user.

Type	string
Default	NULL
Option List:	Option Brief Description NULL NULL replacement Assign a NULL value when VALIDPER is not met. NEAREST Nearest-Neighbor replacement Use the nearest-neighbor algorithm to assign a value when VALIDPER is not met. The output pixel will be set to the input pixel which is closest to the center of the window being analyzed.

In this example, the sample scale factor inverse is 2 (sscale=2) and no other parameter is entered. This implies that the default settings will be used for all the parameters except for sscale. The number of samples will be scaled down by a factor of 2, not scaled up. There will be no reduction in the number of lines because nothing was entered for lscale, and "lscale=1" is the default. Since the default mode of reduction is "SCALE," the mode parameter does not need to be specified.

reduce from=peaks.cub to=reducedPeaks.cub sscale=2.0

GUI for REDUCE

Example GUI Screenshot of the GUI with parameters set to perform a reduction of the input image. The default setting "algorithm=average mode=scale lscale=1 validper=50 vper_replace=NULL" will be used.

The input image before reduction.

Input image for the reduce application Parameter Name: FROM This is the input image that will be reduced.

The image after reduction.

Output image from the reduce application Parameter Name: TO This is the reduced image. Though it has been scaled down so that it can be viewed in a web browser, the essential change can still be observed. The distortion is noticeable because the output file has been reduced in the sample direction but not in the line direction. The output image is half as wide as the input image but is the same height, and the features are compressed in one direction.

Reduce the image by setting the number of samples to 150, and the number of lines to 250. The parameter Mode must be set to "Total" when the ONS and ONL parameters are used.

reduce from=peaks.cub to=totalPeaks.cub mode=total ons=150 onl=250

GUI for REDUCE

Example GUI Screenshot of the GUI with parameters set to perform a sample and line reduction to a total number of pixels. The default settings for "algorithm," "validper," and "vper_replace" will be used.

The input image before reduction.

Input image for reduce application Parameter Name: FROM This is the image that will be reduced.

The image after reduction.

Output image from the reduce application Parameter Name: TO This is the reduced image. Though it has been scaled down so that it can be viewed in a web browser, the essential change can still be observed. The distortion is noticeable because the output cube is not as wide as the input cube, and the features are compressed in one direction. The output cube has 1/3 the number of samples and 1/2 the number of lines as the input cube.