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Bias Correction Properties
The Bias Correction Properties dialog is
used by all higher level calibration procedures that create and
apply image calibrations, including
Create Master Bias,
Express Image Calibration, and others. The
pages of this dialog provide several Bias correction methods for
removing CCD Bias effects from the raw CCD images, including using
a Master Bias frame as well as higher order overscan, underscan,
and other Bias methods. After configuring the chosen methods,
select them using the checkboxes on the Select Methods
page.
Select Methods
Select the Bias correction method(s) by checking
their box on the Select Methods page. More than 1 method can
be applied; for example, the Select Methods page below
indicates that both a Master Bias Frame and a Column
Bias correction will be applied to the raw images.
Master Bias Frame Method
Use this method to subtract a master Bias frame
from each image. The page has a single property, which selects the
master Bias frame from a file. To choose a file containing the
master Bias frame, click[...] and
select its file.
Column Bias Method
Use this method to calculate and subtract a Bias
function of row position evaluated over a range of columns. The
Column Bias Method property selects the type of column Bias
function to be used. Other parameters control the operation of the
selected method.
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Column Bias Properties
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Column Bias Method
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Selects the method used to calculate and apply the
column-direction Bias correction: The Bias is calculated in the
following ways:
1. Mean Value: Calculates the mean value
over the specified range of columns.
2. Median Value: Calculates the median
value over the specified range of columns.
3. Polynomial Fit: Calculates a polynomial
of up to 10 terms for pixels in the specified range of
columns.
4. Erase Line:Reads an erase line from the
image, which is a Bias column calculated at image acquisition time
and stored in an image column for later use.
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Fit Terms
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If method 3, Polynomial Fit is selected,
use this list to select the number of terms in the fit. For
example, use 3 terms to fit a parabola.
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Column Bias Region
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Specifies the region used for the Bias
calculation. If Column Bias Method = 1, 2, or 3 is selected,
then a region of 1 or more columns may be selected. For method 4,
the Erase Line is stored in a single column of the image
array.
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 Keyword
Range
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This selection determines how the rows are
specified for Bias measurements.
Many camera controllers save the column and row
limits of the Bias region as a header keyword. To use this
capability, enter the name of the header keyword that holds the
[column,row] endpoints of the Bias region. A typical name for this
keyword is BIASSEC.
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Min Column
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If Keyword is not selected, this gives the
minimum column number for the Bias calculation. If Column Bias
Method = Erase Line, then this specifies the only column
containing the Erase Line.
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Max Column
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If Keyword is not selected, this gives the
maximum column number for the Bias calculation.
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Row Bias Correction
Use this method to calculate and subtract a Bias
function of column position evaluated over a range of Rows. The
Row Bias Method property selects the type of row Bias
function to be used. Other parameters control the operation of the
selected method.
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Row Bias Properties
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Row Bias Method
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Selects the method used to calculate and apply the
row-direction Bias correction: The Bias is calculated in the
following ways:
1. Mean Value: Calculates the mean value
over the specified range of rows.
2. Median Value: Calculates the median
value over the specified range of rows.
3. Polynomial Fit: Calculates a polynomial
of up to 10 terms for pixels in the specified range of
rows.
4. Erase Line:Reads an erase line from the
image, which is a Bias row calculated at image acquisition time and
stored in an image row for later use.
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Fit Terms
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If method 3, Polynomial Fit is selected,
use this list to select the number of terms in the fit. For
example, use 3 terms to fit a parabola.
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Row Bias Region
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Specifies the region used for the Bias
calculation. If Row Bias Method = 1, 2, or 3 is selected,
then a region of 1 or more rows may be specified. For method 4, the
Erase Line is stored in a single row of the image array.
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Keyword
Range
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This selection determines how the rows are
specified for Bias measurements.
Many camera controllers save the column and row
limits of the Bias region as a header keyword. To use this
capability, enter the name of the header keyword that holds the
[column,row] endpoints of the Bias region. A typical name for this
keyword is BIASSEC.
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Min Row
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If Keyword is not selected, this gives the
minimum row number for the Bias calculation. If Row Bias Method
= Erase Line, then this specifies the only row containing the
Erase Line.
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Max Row
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If Keyword is not selected, this gives the
maximum row number for the Bias calculation.
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Related Topics
Create Master Bias
Create Master Bias
Create Master Flat
Create Illumination Flat
Create Pixel Flat
Express Image Calibration
Mira Pro x64 User's Guide, Copyright Ⓒ 2023 Mirametrics, Inc. All
Rights Reserved.
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