This program can be used to tonematch or equalize the brightness and/or
contrast of the input cubes prior to mosaicking.
All cubes must be in a common map projection as this program will use the
mapping information to gather statistics in overlapping areas. This is done on a
band-by-band basis as well. The statistics are used in a least squares solution
to determine multiplicative and additive corrections to each image. The user has
the option to stop the processing and examine the statistics and corrective factors.
Alternatively, the processing can continue and the corrective factors will be applied
to each image (by making sure the APPLY checkbox is ticked).
The actual equation to be used for each band in each cube is:
While equalizing, the user can think of adjusting the brightness and/or contrast of the cubes.
The default is to adjust both, however, if the brightness (average) of all the cubes is the same,
then simply adjusting the contrast may suffice. Likewise, if the standard deviation of all the
cubes is similar, then a contast adjustment is not necessary. Adjusting for contrast only implies
the BASE values will be held to zero. Similarly, adjust for brightness implies the MULT values
will be held to one.
The BASE and MULT values are computed independently for each image, therefore we have two
least squares computations with N unknowns, where N is the number of cubes to be equalized.
The overlaps, M, between all the cubes are computed and in some cases M < N. This implies
an underdetermined system. The program will report an error if this occurs. You can hold one or
more cubes to alleviate this problem. Holding a cube forces MULT and BASE to 1.0 and 0.0
respectively.
If the APPLY option is selected, the equalized cubes will be named the same as the input cubes
with the addition of a '.equ' prior to the '.cub' extension.
This application replaces the following
applications existing in previous versions of Isis, which have been deprecated
from the current version of Isis:
b4equal
equalizer
History
Kay Edwards
1994-05-24
Original version
Elizabeth Ribelin
2005-06-25
Ported to Isis 3.0
Elizabeth Ribelin
2005-10-04
Changed categoryItem to Photometry and Radiometry
Brendan George
2005-11-07
Added application test
Elizabeth Miller
2006-01-12
Made SD default contrast mode (PCA may have errors)
Jeff Anderson
2007-07-16
Fixed memory leak
Jeff Anderson
2008-04-09
Modified to solve system using QRD which is faster the SVD
Steven Lambright
2008-05-12
Removed references to CubeInfo
Tracie Sucharski
2008-06-12
Modified call LeastSquares Solve due to change to LeastSquares
Solve method.
This file will contain the statistics of all of the overlapping areas
in every band along with the computed equalizing factors
(BASE and MULT). Specifying this output file is optional.
List of cubes that are to be held in the equalization.
An additive and a multiplicative factor of 0 and 1 will be applied
to all cubes that were held. All cubes listed in this file must
also be contained in FROMLIST.
This option allows the user to decide whether they want to do the
equalization calculations only, or do the calculations and apply the
correction to the images. If the APPLY option is not selected, you must
specify a TO file. If it is selected you can still optionally specify a TO file and
the MULT/BASE values will be applied to each input cube. The output cubes
will be named the same with the exception of ".equ" extension (e.g. "foobar.cub"
becomes "foobar.equ.cub").
Choose the fit option to select the algorithm to use to
adjust the pixel values. The CONTRAST mode will equalize
using only a multiplier (the base will be set to 0.0), and
the BRIGHTNESS mode will equalize using only a base
(the multiplier will be set to 1.0). The BOTH option will equalize
using both a base and a multiplier. In most cases this
option will give you the best results.
Type
string
Default
BOTH
Option List:
Option
Brief
Description
BOTH
Adjust the Brightness and Contrast of the images.
This option will use an algorithm that equalizes
both the brightness and contrast of the images.
CONTRAST
Adjust the Contrast of the images only
This option will use an algorithm that only equalizes
the contrast of the images. This option should only
be used if the brightness of the images are already
close.
BRIGHTNESS
Adjust the Brightness of the images only
This option will use an algorithm that only equalizes
the brightness of the images. This option should be
used only if the variance/standard deviation of the
images is close.
The input images can be mosaicked together using one of two contrast
modes, principal component analysis or standard deviation.
The pricipal component analysis mode fits pixels using the slope
of a line of best fit of brightness between the cubes, and the
standard deviation mode fits pixels using the ratio of the
standard deviations of the brightness values in each cube.
This option only effects the computation of the MULT.
Type
string
Default
SD
Option List:
Option
Brief
Description
SD
Standard Deviation Fit Mode
Calculates the contrast adjustment using the ratio of the standard
deviations of the brightness values in each cube.
PCA
Principal Component Analysis Fit Mode
Calculates the contrast adjustment using the slope of a line of best fit
of the brightness values between the two cubes.
This option allows the user to decide whether they want to weight the least squares solution based on how
large the overlap area is, or if they want no weighting at all.
This example shows the use of the equalizer application. The defaults are adjusting both the
brightness and contrast in the Standard Deviation Fit Mode (SD).
Specify a list of Io images to equalize along with a holding list that enables the necessary
calculations to be performed. All other options are at default values.
Input Image
Mosaic of unequalized input images
Mosaic of the input images for equalizer
Parameter Name:
FROMLIST
This is a a small section of the input images for the equalizer example mosaicked together.
Output Image
Output image of mosaic showing results of the equalizer application.
Mosaic of the output images for equalizer
This is a small section of the equalized output images mosaicked together.