overscan in the middle of the image
kanaan wrote on Apr 08, 2008
Hi there,
short story: how do I tell the overscan fitting routine to only use a part of a single column? it seems that it is ok with the single column but it then wants to fit to the ENTIRE column.
long story:
I have a set of weird images without overscan region. It seems the bias level is going up and down during the night. I realized there is one bad column on this chip which is just bias. So I decided to use it as overscan:
ecl> lpar ccdproc
images = "@flatlist" List of CCD images to correct
(output = "") List of output CCD images
(ccdtype = "") CCD image type to correct
(max_cache = 0) Maximum image caching memory (in Mbytes)
(noproc = no) List processing steps only?\n
(fixpix = no) Fix bad CCD lines and columns?
(overscan = yes) Apply overscan strip correction?
(trim = no) Trim the image?
(zerocor = yes) Apply zero level correction?
(darkcor = no) Apply dark count correction?
(flatcor = no) Apply flat field correction?
(illumcor = no) Apply illumination correction?
(fringecor = no) Apply fringe correction?
(readcor = no) Convert zero level image to readout correction?
(scancor = no) Convert flat field image to scan correction?\n
(readaxis = "line") Read out axis (column|line)
(fixfile = "") File describing the bad lines and columns
(biassec = "[179:179,230:500]") Overscan strip image section
(trimsec = "") Trim data section
(zero = "../d5apr10/Dark.fits") Zero level calibration image
(dark = "") Dark count calibration image
(flat = "../f5apr10/Flat.fits") Flat field images
(illum = "") Illumination correction images
(fringe = "") Fringe correction images
(minreplace = 1.) Minimum flat field value
(scantype = "shortscan") Scan type (shortscan|longscan)
(nscan = 1) Number of short scan lines\n
(interactive = yes) Fit overscan interactively?
(function = "legendre") Fitting function
(order = 1) Number of polynomial terms or spline pieces
(sample = "*") Sample points to fit
(naverage = 1) Number of sample points to combine
(niterate = 1) Number of rejection iterations
(low_reject = 3.) Low sigma rejection factor
(high_reject = 3.) High sigma rejection factor
(grow = 0.) Rejection growing radius
(mode = "ql")
see, the Y section goes from 230 to 500, below 230 the column is ok.
well, all sounds fine, however, when I run ccdproc it is actually fitting the entire column. I turned interactive to YES and I can see the plot being made all the way from 1 to 512, and it is not just the plot, it is the fit too. The fitted function (a constant = lengendre order 1) shown as a dashed line is in the middle of the plot. Basically I get a step for the data and a horizontal line in the middle of the step.
any suggestions welcome, thanks,
Antonio
short story: how do I tell the overscan fitting routine to only use a part of a single column? it seems that it is ok with the single column but it then wants to fit to the ENTIRE column.
long story:
I have a set of weird images without overscan region. It seems the bias level is going up and down during the night. I realized there is one bad column on this chip which is just bias. So I decided to use it as overscan:
ecl> lpar ccdproc
images = "@flatlist" List of CCD images to correct
(output = "") List of output CCD images
(ccdtype = "") CCD image type to correct
(max_cache = 0) Maximum image caching memory (in Mbytes)
(noproc = no) List processing steps only?\n
(fixpix = no) Fix bad CCD lines and columns?
(overscan = yes) Apply overscan strip correction?
(trim = no) Trim the image?
(zerocor = yes) Apply zero level correction?
(darkcor = no) Apply dark count correction?
(flatcor = no) Apply flat field correction?
(illumcor = no) Apply illumination correction?
(fringecor = no) Apply fringe correction?
(readcor = no) Convert zero level image to readout correction?
(scancor = no) Convert flat field image to scan correction?\n
(readaxis = "line") Read out axis (column|line)
(fixfile = "") File describing the bad lines and columns
(biassec = "[179:179,230:500]") Overscan strip image section
(trimsec = "") Trim data section
(zero = "../d5apr10/Dark.fits") Zero level calibration image
(dark = "") Dark count calibration image
(flat = "../f5apr10/Flat.fits") Flat field images
(illum = "") Illumination correction images
(fringe = "") Fringe correction images
(minreplace = 1.) Minimum flat field value
(scantype = "shortscan") Scan type (shortscan|longscan)
(nscan = 1) Number of short scan lines\n
(interactive = yes) Fit overscan interactively?
(function = "legendre") Fitting function
(order = 1) Number of polynomial terms or spline pieces
(sample = "*") Sample points to fit
(naverage = 1) Number of sample points to combine
(niterate = 1) Number of rejection iterations
(low_reject = 3.) Low sigma rejection factor
(high_reject = 3.) High sigma rejection factor
(grow = 0.) Rejection growing radius
(mode = "ql")
see, the Y section goes from 230 to 500, below 230 the column is ok.
well, all sounds fine, however, when I run ccdproc it is actually fitting the entire column. I turned interactive to YES and I can see the plot being made all the way from 1 to 512, and it is not just the plot, it is the fit too. The fitted function (a constant = lengendre order 1) shown as a dashed line is in the middle of the plot. Basically I get a step for the data and a horizontal line in the middle of the step.
any suggestions welcome, thanks,
Antonio
Francisco Valdes wrote on Apr 08, 2008
Hello Antonio,
I'm afraid that the way an "overscan" is defined and used by ccdproc is the entire column matched to the data. You can put in an image section but the second part of the section is ignored. So your options are to determine the bias value separately and either subtract it (the constant) with imarith/imexpr or replace the entire column you are using right now by that value with imreplace and a section.
Let me know if you want more suggestions.
Yours,
Frank Valdes
I'm afraid that the way an "overscan" is defined and used by ccdproc is the entire column matched to the data. You can put in an image section but the second part of the section is ignored. So your options are to determine the bias value separately and either subtract it (the constant) with imarith/imexpr or replace the entire column you are using right now by that value with imreplace and a section.
Let me know if you want more suggestions.
Yours,
Frank Valdes
Last post on Apr 08, 2008