Create Master Flat


The Create Master Flat command combines flat frames to create a calibration image for correcting variations in both sensitivity and illumination. Since the sensitivity variations are usually dependent on wavelength, the master flat may be applied to images by matching the FILTER keyword or be used for an approximate correction without considering the filter. Segregation by FILTER is configured using settings in the Selection Criteria window (see below). To utilize separate corrections for illumination and sensitivity, use the the Create Illumination Flat and Create Pixel Flat commands instead of this command. 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 also create multiple output images by combining images in groups according to their FILTER keyword.

Create Master Flat Properties

Profile [|>]

Manages the parameter collection used by this dialog. See Profile Control for details.

Select

For the general case, this button 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.

Base name of the Master Flat(s) to be created:

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.

Create in subfolder:

For the general case, enter the name of the subfolder where the Master 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

For the general case, 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 MasterFlat.fts exists and this box is not checked, then the output file will be named MasterFlat_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

For the general case, check this box to display the resulting Master Flat.

 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 a dialog for specifying how raw flat frames are selected and combined using a filter keyword.

Flat Frame Selection Criteria Properties

Filter Selection Criteria

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, MasterFlat_B.fts.

Filter Keyword

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.

Filter Name

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.

 Select individual flats using the signal range

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.

Min Value

Specify the minimum acceptable median signal value over the central 10% of the raw image width and height.

Max Value

Specify the maximum acceptable median signal value over the central 10% of the raw image width and height.

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 Image Combining Methods 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 Image Combining Methods.

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 - Alpha Clipped method uses 2 Properties: the number of highest--value pixels to clip ("High count") and the number of lowest-value pixels to clip ("Low count").

[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.

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 the dark (thermal) correction 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 Illumination Flat, Create Pixel Flat, Select Source Images, Express Image Calibration, Combine Image Set, Combine Files