Create Pixel Flat
The Create Pixel Flat command combines flat
frames to create a correction for sensitivity variations among
pixels. Usually these variations are a function of wavelength, so a
companion illumination is often used to correct variations in
illumination. The individual flat frames may be calibrated by
applying bias and dark corrections during processing, then combined
to create an output image having higher signal to noise ratio than
any single flat frame. This command can create multiple output
flats by combining images in groups according to their FILTER
keyword.
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The Create Pixel Flat command opens from
the Image Window > Process >
Calibration menu and button
on the Main Toolbar. The "immediate"
form, shown first, opens when an image or image set is displayed in
the top-most window. The general form can be used to select source
images from folders, windows, or by matching templates.
Create Pixel Flat Properties
Profile [|>]
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Manages the parameter collection used by this
dialog. See
Profile Control for details.
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Select
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Opens the
Select Source Images dialog for selecting raw images
to be processed into the final calibrated result. The name of the
first selected file or displayed image
is listed in the field to the right.
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Base name of the Pixel Flat(s) to be
created:
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Enter the name to use as a template for the output
flat(s) or click [...] to browse
files and choose the name from a folder. If multiple flats are
created, this name is appended with identifying characters such as
the filter name.
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Create in subfolder:
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Enter the name of the subfolder where the Pixel
Flat will be created. This is a subfolder of the folder containing
the first raw flat frame in the source image list.
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Overwrite existing
files
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Check this box to overwrite an existing file
having the same file name in the output subfolder. If this box is
not checked and a file of the same name exists, an underscore and
number will be appended to the output file. For example, if
PixelFlat.fts exists and this box is
not checked, then the output file will be named PixelFlat_2.fts
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Combining Strategy...
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Click this button to set properties for combining
the flat frames. This opens the
Image Combining Strategy dialog.
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Selection Criteria...
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Click this button to set properties for selecting
raw flat frames based on their range in central signal level. This
allows Mira to use only raw flats that are statistically valid by
having a minimum signal but not saturated beyond a maximum
signal.
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Bias Correction...
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Click this button to open the
Bias Correction Properties dialog for applying a bias
correction to the raw flat frames.
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Dark Correction...
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Click this button to open the
Dark Correction Properties dialog for applying a dark
correction to the raw flat frames.
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Display result
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Check this box to display the resulting Pixel
Flats.
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Log Processing
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Check this box to list verbose processing messages
in a
Text Editor window. If the window already exists from
previous processing by this or another calibration command, then
its contents are appended.
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Log processing to:
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The drop list provides options for listing
messages:
--None -- lists no
processing messages
Messages lists
processing messages in the "Calibration Message Log" text area at
the bottom of the dialog.
Text Editor lists
processing messages in a
Text Editor window named "Calibration Message
Log".
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Notification:
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Select the type of notification Mira issue when
processing is finished:
Do nothing Mira
quietly ends the processing without notification.
Beep creates a
notification sound,
Message displays a
notification message in a top level dialog that locks out Mira use
until you dismiss the message.
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Selection Criteria
The [Selection
Criteria...] button opens a dialog for specifying how raw
flat frames are selected and combined using a filter keyword.
Flat Frame Selection Criteria
Properties
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Filter Selection Criteria
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Chooses how a filter keyword may be used to create
a single output flat or a set of output flats for different
filters. The 3 options are as follows:
1. Select all flats without choosing a
filter: Creates a single output flat by ignoring possible
filter differences among the source images.
2. Select only flats that match a single
filter: Creates a single output flat using only source images
having a specific value of the filter keyword. In this case, both
the name of the filter keyword and the target filter value must be
specified, for example, Filter Keyword = FILTER and Filter Name = R.
3. Create a library of flats for different
filters: Creates one or more output flats by combining only
flats having the same value of the filter keyword. For example, if
the source images use B, V, and R filters, this option would create
separate output flats for the B, V, and R filters. The value of the
filter keyword for each group is appended to the base name as the
name of the output flat, for example, PixelFlat_B.fts.
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Filter Keyword
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Specify the name of the filter keyword in the raw
flat frames. When Filter Selection
Criteria options 2 and 3 are selected, this property
specifies the name of the filter keyword. Typically, this is the
FITS format standard FILTER, although
any keyword may be used.
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Filter Name
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Specified the value of the Filter keyword in the
raw flat frame. When Filter Selection
Criteria option 2 is selected, this property specifies the
filter name encoded in the Filter keyword. For example, if the
images use FILTER = 'R', then this
property would be set to R.
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Select individual flats
using the signal range
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Check this box to select raw images based on their
median central signal. Setting upper and lower limits assures that
raw images underexposed or overexposed are not processed into the
output flats.
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Min Value
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Specify the minimum acceptable median signal value
over the central 10% of the raw image width and height.
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Max Value
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Specify the maximum acceptable median signal value
over the central 10% of the raw image width and height.
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Canceling the Processing
If you wish to cancel the task before it completes,
either click the [Cancel] button on
the Progress window or press the Esc
key.
Tip
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To abort the calibration before it is finished,
click the [Cancel] button on the
progress window or press the Esc key.
Mira will prompt you for confirmation to quit. If you confirm, the
task will terminate immediately.
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Bias Correction
Click the [Bias
Correction...] button to configure several types of bias
corrections that can be applied to the raw flat frames during
processing. This button opens the
Bias Correction Properties dialog.
Dark Correction
Click the [Dark
Correction...] button to configure several types of dark
corrections that can be applied to the raw flat frames during
processing. This button opens the
Dark Correction Properties dialog.
Processing Messages
Mira creates a highly detailed log of processing
messages to document every step of the processing pipeline. These
messages may be sent to a global
Text Editor window or to a message area at the bottom
of the command dialog. If theMessages
option is selected for the List results
in option, Miralogs processing messages in the Results box at the bottom of the dialog. Messages
appear after the processing finishes. The Results field has a right-click menu as shown
below. Using this menu you can save messages to a text file and
copy from the box to the Windows clipboard or a Mira
Text Editor. Only selected (highlighted) text is
copied. Commands for editing and copying the text are available in
a pop-up menu opened by right-clicking inside the results box. The
menu is shown below. You can also elect to save the messages to a
Text Editor which offers similar functionality as
well as printing capability.
To prevent accidental deletion of calibration
messages, you cannot clear text simply by highlighting and deleting
the text using the mouse. To clear messages, you must use the
Clear command in the pop-up menu.
Related Topics
Calibrating Images
Create Master Bias
Create Master Dark
Create Master Flat
Create Illumination Flat
Image Combining Strategy
Select Source Images
Express Image Calibration
Combine Image Set
Combine Files
Mira Pro x64 User's Guide, Copyright Ⓒ 2023 Mirametrics, Inc. All
Rights Reserved.
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