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Flat Correction Properties
The Flat Correction Properties methods are
used by
Express Image Calibration to calibrate source
images. The pages of this dialog provide several types of flat
field corrections for removing variations in illumination and
wavelength-dependent sensitivity across the sensor. The available
options include using a single master flat frame to apply both
illumination and sensitivity corrections and the option of using
separate corrections for illumination and sensitivity. After
configuring the desired flat field methods, select them using the
checkboxes on the Select Methods page.
All flat field correction methods offer the option
to normalize the flats to a central signal level of 1.0 so that,
when dividing the flat correction, the central signal of the source
image is retained. Properly created flats are usually saved with
32-bit and 64-bit real pixels and are pre-normalized to 1.0. If
using flats having 8, 16, or 32-bit integer pixels, you will need
to use the normalization option and select the Normalization
statistics on the property page of the selected method.
To use this method correctly, both the CCD bias and
dark (thermal) corrections have already been applied to the master
flats and source images.
Select Methods
Select the flat correction method (or no dark
correction) by checking the appropriate box on the Select
Methods page. Since the Master Flat Frame incorporates both the
illumination Flat and Pixel Flat corrections in a single flat
frame, you cannot select the Master Flat method if using
either of the Illumination Flat or Pixel Flat
corrections.
Master Flat Frame
Use this method to correct source images for
variations in both illumination and sensitivity. Since sensitivity
variations are usually wavelength dependent, this method gives good
results when the filter used to acquire the flat field frames is
the same as used to acquire the source images.
This method can be configured in 3 ways: 1) to
apply the master flat without regard for the filter, 2) process
only source images using a master flat that matches the specified
filter, or 3) search the list of master flats for a match to the
filter used for the source image. When filter matching is used,
Mira chooses the first flat in the list that matches by filter.
Master Flat Properties
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Browse
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Click this button to open a file browser for
selecting flat files to populate the file list window.
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Clear List
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Click this button to clear the current file list
appearing in the file list window.
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 Append Files
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Check this box to append browsed files to the
files already appearing in the file list window. If unchecked, the
browsed files replace files appearing in the window.
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Save List
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Check this box to save the file list when exiting
the Flat Correction Properties dialog.
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Criteria for choosing flats from the list
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These options control how flats are selected for
use from those in the file list window.
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 Use all flats without
matching the filter: This option to apply the first flat in the
list, regardless of its filter.
Select flats and
images that match the specified filter value: This option
assures that only those images and flats are used if they match a
specified target filter, even if the flats and source images use a
variety of filters. This option requires specifying both the filter
keyword and the filter value to be used for matching.
Match flats to images
using the value of the specified filter: Check this option to
have Mira search the flat list for the first flat that matches the
filter used for the source image. This option requires specifying
the filter keyword used for matching flats to source images.
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Filter Keyword
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When filer matching is used (options 2 and 3), the
filter keyword must be used to determine whether the flat matches
the source image. Usually this keyword is named FILTER, but any name can be used, even if it does
not actually apply to an optical filter.
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Filter Value
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When a specific filter is to be matched (Option
2), this value specifies the name of the filter to be used.
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Normalize to 1.0
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Check this box to normalize the flat to a
reference brightness of 1.0 before applying to the source
image.
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Normalization...
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Click this button to open the Region Statistics
dialog for configuring the calculation of the statistics used to
normalize the flat frame to a reference brightness of 1.0.
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Error value for divide by 0
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Enter the numeric value used to replace pixels in
the corrected image that correspond to the location of a 0 pixel in
the flat.
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Illumination Flat
Use this method to correct the source images for
variations in illumination across the sensor. This method is
usually implemented along with a separate Pixel Flat to
correct wavelength-dependent sensitivity (see below)..When using
this method, the sensitivity variations are usually corrected using
the Pixel Flat method described below.
A complete illumination correction is actually the
superposition of several individual corrections involving, off axis
illumination falloff, mechanical vignetting, and other effects.
Usually, these effects are present in a single illumination flat
but may also be applied as separate corrections. For this reason,
the Illumination flat method can apply 1 or more corrections to the
source images simply by selecting the 1 or more images containing
the target corrections.
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Illumination Flat Properties
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Browse
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Click this button to open a file browser for
selecting flat files to populate the file list window.
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Clear List
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Click this button to clear the current file list
appearing in the file list window.
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Append Files
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Check this box to append browsed files to the
files already appearing in the file list window. If unchecked, the
browsed files replace files appearing in the window.
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Save List
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Check this box to save the file list when exiting
the Flat Correction Properties dialog.
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Normalize to 1.0
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Check this box to normalize the flat to a
reference brightness of 1.0 before applying to the source
image.
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Normalization...
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Click this button to open the Region Statistics
dialog for configuring the calculation of the statistics used to
normalize the flat frame to a reference brightness of 1.0.
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Error value for divide by 0
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Enter the numeric value used to replace pixels in
the corrected image that correspond to the location of a 0 pixel in
the flat.
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Pixel Flat
Use this method to correct the source images for
wavelength-dependent variations in pixel-to-pixel sensitivity. This
method is usually configured to match a pixel flat to the source
image using a filter keyword from the image headers. Typically, the
illumination variations are corrected using the Illumination
Flat method described above.
This method can be configured in 3 ways: 1) to
apply the pixel flat without regard for the filter, 2) process only
source images using a pixel flat that matches the specified filter,
or 3) search the list of pixel flats for a match to the filter used
for the source image. When filter matching is used, Mira chooses
the first flat in the list that matches by filter.
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Pixel Flat Properties
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Browse
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Click this button to open a file browser for
selecting flat files to populate the file list window.
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Clear List
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Click this button to clear the current file list
appearing in the file list window.
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Append Files
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Check this box to append browsed files to the
files already appearing in the file list window. If unchecked, the
browsed files replace files appearing in the window.
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Save List
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Check this box to save the file list when exiting
the Flat Correction Properties dialog.
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Criteria for choosing flats from the list
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These options control how flats are selected for
use from those in the file list window.
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|
|
Use all flats without
matching the filter: This option to apply the first flat in the
list, regardless of its filter.
Select flats and
images that match the specified filter value: This option
assures that only those images and flats are used if they match a
specified target filter, even if the flats and source images use a
variety of filters. This option requires specifying both the filter
keyword and the filter value to be used for matching.
Match flats to images
using the value of the specified filter: Check this option to
have Mira search the flat list for the first flat that matches the
filter used for the source image. This option requires specifying
the filter keyword used for matching flats to source images.
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Filter Keyword
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When filer matching is used (options 2 and 3), the
filter keyword must be used to determine whether the flat matches
the source image. Usually this keyword is named FILTER, but any name can be used, even if it does
not actually apply to an optical filter.
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Filter Value
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When a specific filter is to be matched (Option
2), this value specifies the name of the filter to be used.
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Normalize to 1.0
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Check this box to normalize the flat to a
reference brightness of 1.0 before applying to the source
image.
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Normalization...
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Click this button to open the Region Statistics
dialog for configuring the calculation of the statistics used to
normalize the flat frame to a reference brightness of 1.0.
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Error value for divide by 0
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Enter the numeric value used to replace pixels in
the corrected image that correspond to the location of a 0 pixel in
the flat.
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Related Topics
Calibrating Images
Express Image Calibration
Mira Pro x64 User's Guide, Copyright Ⓒ 2023 Mirametrics, Inc. All
Rights Reserved.
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