The fors_img_screen_flat recipe

fors_img_screen_flat

Synopsis

Compute master screen flat frame

Description

After bias subtraction, the input flat field frames are combined using the given stack method. The combined frame is finally normalised dividing it by its large scale illumination trend. The large scale trend is obtained by applying a median filter with a large kernel. To avoid boundary effects, the median filter is applied only to the specified region.

The overscan regions, if present, are removed from the result.

Input files

DO category:               Type:       Explanation:         Required:
SCREEN_FLAT_IMG            Raw         Screen flat field    Y
MASTER_BIAS                Raw         Master bias          Y

Output files

DO category:               Data type:  Explanation:
MASTER_SCREEN_FLAT_IMG     FITS image  Master screen flat field

Constructor

cpl.Recipe("fors_img_screen_flat")

Create an object for the recipe fors_img_screen_flat.

import cpl
fors_img_screen_flat = cpl.Recipe("fors_img_screen_flat")

Parameters

fors_img_screen_flat.param.stack_method

Frames combination method (str; default: ‘average’) [default=”average”].

fors_img_screen_flat.param.minrejection

Number of lowest values to be rejected (int; default: 1) [default=1].

fors_img_screen_flat.param.maxrejection

Number of highest values to be rejected (int; default: 1) [default=1].

fors_img_screen_flat.param.klow

Low threshold in ksigma method (float; default: 3.0) [default=3.0].

fors_img_screen_flat.param.khigh

High threshold in ksigma method (float; default: 3.0) [default=3.0].

fors_img_screen_flat.param.kiter

Max number of iterations in ksigma method (int; default: 999) [default=999].

fors_img_screen_flat.param.xradius

Median filter x radius (unbinned pixels) (int; default: 50) [default=50].

fors_img_screen_flat.param.yradius

Median filter y radius (unbinned pixels) (int; default: 50) [default=50].

fors_img_screen_flat.param.degree

Degree of fitting polynomial (int; default: -1) [default=-1].

fors_img_screen_flat.param.sampling

Sampling interval for fitting (int; default: 100) [default=100].

The following code snippet shows the default settings for the available parameters.

import cpl
fors_img_screen_flat = cpl.Recipe("fors_img_screen_flat")

fors_img_screen_flat.param.stack_method = "average"
fors_img_screen_flat.param.minrejection = 1
fors_img_screen_flat.param.maxrejection = 1
fors_img_screen_flat.param.klow = 3.0
fors_img_screen_flat.param.khigh = 3.0
fors_img_screen_flat.param.kiter = 999
fors_img_screen_flat.param.xradius = 50
fors_img_screen_flat.param.yradius = 50
fors_img_screen_flat.param.degree = -1
fors_img_screen_flat.param.sampling = 100

You may also set or overwrite some or all parameters by the recipe parameter param, as shown in the following example:

import cpl
fors_img_screen_flat = cpl.Recipe("fors_img_screen_flat")
[...]
res = fors_img_screen_flat( ..., param = {"stack_method":"average", "minrejection":1})

See also

cpl.Recipe for more information about the recipe object.

Bug reports

Please report any problems to Jonas M. Larsen. Alternatively, you may send a report to the ESO User Support Department.