Create Illumination Flat

The Create Illumination Flat command combines flat frames to create an illumination correction image that maps variations in illumination. Usually these variations are taken to be independent of wavelength, whereas the correction for sensitivity variations, which are dependent on wavelength, are accomplished using a Pixel Flat. The individual flat frames may be calibrated during processing by applying bias and dark corrections, then combined to create the master flat having higher signal to noise ratio than any single flat frame.

The Create Illumination 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 Illumination Flat Properties

Profile [\|>]	Manages the parameter collection used by this dialog. See Profile Control for details.
Select	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.
Name of the Illumination Flat to be created:	Enter a name for the output master flat or click [...] to browse files for choosing the name from a folder.
Create in subfolder:	Enter the name of the subfolder where the illumination flat will be created. This is a subfolder of the folder containing the first raw flat frame in the source image list.
Overwrite existing files	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 IlluminationFlat.fts exists and this box is not checked, then the output file will be named IlluminationFlat_2.fts
Combining Strategy...	Click this button to set properties for combining the flat frames.
Selection Criteria...	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.
Bias Correction...	Click this button to open the Bias Correction Properties dialog for applying a Bias correction to the raw flat frames.
Dark Correction...	Click this button to open the Dark Correction Properties dialog for applying a dark correction to the raw flat frames.
Display result	Check this box to display the resulting illumination flats.
Log Processing	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.
Log processing to:	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".
Notification:	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.

Selection Criteria

The [Selection Criteria...] button opens the Flat Frame Selection Criteria dialog for specifying how raw flat frames are selected and combined using a filter keyword.

Combining Strategy

The [Combining Strategy...] button opens the Image Combining Properties dialog for configuring how pixel values are combined in the final processing step, after bias and dark corrections are applied to the raw flat frames. For a description of the properties set in this dialog, see the Statistical Estimators for Image Combining and Region Statistics topics.

Image Combining Properties
Combining Method	This list box selects the type of processing used to combine the image values. These are described in Statistical Estimators for Image Combining. If the combining method takes Properties, these are presented in 1 or 2 fields to the right of the Method selection box. Some methods have no Properties, so no fields are visible. For example, in the picture above, the Mean - Sigma Clipped method uses 2 Properties: the upper number of sigma's to clip ("High sigma") and the lower number of sigma's to clip ("Low sigma").
[Normalization Statistic]	Click this button to open the Region Statistics dialog for selecting normalization properties.
Target Pixel Type	Select a Pixel Type for the output image that can accommodate the increased signal and dynamic range of the combined images. For example, if combining a large number of 16-bit integer type images it is usually prudent to set the Pixel Type of the output image to 32-bit real.
Smoothing Properties	This group specifies the smoothing filter used to remove high frequency information from the illumination flat, leaving only a low frequency map of illumination changes..
Columns	Specifies the number of columns in the smoothing filter width.
Rows	Specifies the number of rows in the smoothing filter height.

Canceling the Combining Task

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	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.

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.