Image Calibration Features
This Brief describes the capabilities of Mira's Image Calibration Pipeline. The Image Calibration package is extremely versatile, allowing you to choose the combination of tasks needed to calibration a particular data set. A calibration procedure may include any or all of the steps and methods described in this Brief, or the procedure might involve just a single step, such as changing a keyword name in an image header. Not described here is the separate Express Calibration command available for doing quick calibration using just the basic calibration steps.
Also see: Advanced Image Calibration
Calibration Methods
| Procedural Step | Methods | Options | AP | Pro | MX |
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Rename File Extensions |
Convert image name extensions like "fits" to "fts" |
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Modify Image Headers (Multiple methods may be selected) |
Add keywords and values | Add new keywords to the image header or append keywords like HISTORY. |
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| Change keyword value | Replace the value of existing keywords. |
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| Rename keyword | Rename keywords like EXPOSURE to EXPTIME |
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Bias Correction (Multiple methods may be selected) |
Create master bias frame |
Combine raw bias frames using mean, median, sigma clip, and min/max
rejection. Note: Mira Pro and MX add more methods and options. |
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| Apply master bias frame | Created or specified from a displayed image or a file. |
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| Apply column bias correction | Mean Column Bias |
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| Median Column Bias |
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| Erase Line (column) |
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| Polynomial fit to column overscan or underscan, using 1 to 10 coefficients. |
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| Apply row bias correction | Mean Row Bias |
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| Median Row Bias |
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| Erase Line (row) |
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| Polynomial fit to row overscan or underscan, using 1 to 10 coefficients. |
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| Apply bias value | Specify bias value |
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| Read a reference bias value from the image header |
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Dark Correction |
Create master dark frame |
Combine raw dark frames using mean, median, sigma clip, and min/max
rejection. Note: Mira Pro and MX add more methods and options. |
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| Create a library of master dark frames based on exposure | Combine raw dark frames by mean, median, sigma clipping, and other numerical methods. |
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| Apply master dark frame | Subtract a dark frame |
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| Scale dark frame by exposure time |
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| Optimize dark subtraction by minimal residual noise |
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| Apply a library of master dark frames selected by exposure | Subtract a dark frame |
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| Scale dark frame by exposure time |
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| Optimize dark subtraction by minimal residual noise |
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Flat Field Correction |
Create master flat frame |
Combine and normalize raw flats using mean, median, sigma clip, and
min/max rejection. Note: Mira Pro and MX add more methods and options. |
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| Create a library of master flat frames based on filter. | Identify raw source files by filter type, then combine using the mean, median, sigma clipping, and other methods. |
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| Apply a single master flat frame | Divide a normalized flat field correction into the images. |
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| Apply a library of master flat frames selected by filter. | Divide a normalized flat field correction into the images matched by filter name. |
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Cosmetic Repairs (Multiple methods may be selected) |
Apply blemish mask | Correct regions of defective rows, columns, rectangles, and points based on a coordinate map. |
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| Apply pixel mask | Correct defective pixels based on a coordinate map. |
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| Apply cosmic ray filter | Identify and correct defective pixels based on neighborhood deviation. |
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Trim Images |
Crop images to specified dimensions or using a trim-section keyword from the image header. |
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Change Data Type |
Forces the output data type to a given type. Otherwise, Mira expands the data type to accommodate the precision in the processing. |
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Additional Features
- An elegant GUI allows you to save, load, and visually configure procedures by name.
- Processes a displayed image or image set, or a folder of undisplayed image files.
- "Undo" option for displayed images.
- Select of raw image files by matching a filename template, a file name list, or a keyword (e.g., IMAGETYP = 'dark') for each of the image types: bias, dark, flat, and data.
- Allows choice of pre-existing master calibration frames or creation of master frames as part of the pipeline.
- Creates and/or applies a single master dark or flat frame, or a library of master darks or flats.
- Automatic data type promotion preserves the precision of calibrated images.
- Full image header updating with processing results and notes.
- Detailed processing history added to each image. If you re-run calibration on the same images, Mira will not re-do steps that have already been performed on individual images.
- Verbose messaging option creates a text file containing a detailed log of the calibration procedure.