Appendix 3 - Creating CCD Windows for Imaging

  1. Vertical Binning
  2. Horizontal Binning
  3. Window Positions
  4. Window Parameters
  5. File Layout & Examples
    1. FORS.WINDOW
    2. RCA-STAN.WINDOW
    3. GEC17-PAIR2.WINDOW
    4. TEK1K_DIRECT.WINDOW
    5. TEK1K_DIRECT_CEN.WINDOW
    6. TEK1K_CEN_100.WINDOW
    7. THOMSON_F1.WINDOW
    8. THOMSON_F1_CENTRE.WINDOW
    9. THOMSON_BIN2.WINDOW
    10. THOMSON_F1_TEST.WINDOW
  6. Time Series Windows


Introduction The Telescope & Optics The Detectors
The Imaging Cameras An Imaging Cookbook The Data you Take Away
Exposure times OFFSET_RUN files CCD Windows Data Catalogs
On-line Reduction Filters Flat-fields Blank Fields Orientation Shutters

Back Contents Next

Last Contents Next

NB: Some of the following discussion is irrelevant to direct CCD imaging. However, it is all included for completeness. Of the example files, numbers 4-10 are the most directly relevant to direct imaging. 

DEFINITIONS

A window is a rectangularly bounded region anywhere inside the data digitization area which includes the physical CCD chip and typically extends beyond it by a number of rows and columns in each direction. The hardware supports single and dual windows which may be placed anywhere in the digitization area.

The current software allows only dual windows, except for time series mode where only a single window is allowed. The present program also requires  that the two windows begin on the same starting row and finish on the same  end row. This restriction may be relaxed in later software. For normal  readout mode, single windowing is simulated by defining either the left or  the right window as a single column of the bias overscan region or by  simply butting the two windows together.

For the purpose of binning the data, each window may be divided into one, two or three horizontal binning fields (summing columns). Both windows together may also be divided into one, two or three vertical binning fields (summing rows). The hardware currently requires that the vertical binning be the same for both windows, though the horizontal binning can be different.

In this appendix, we use the following terminology: A line is a single row of CCD pixels before binning and a row is a series of image data elements after binning. Pixels are individual detector elements on the CCDchip or their direct equivalent in the pre-scan or over-scan areas, BEFORE binning. Bins are the digitization or image data elements AFTER binning.  For example, one row of 193 bins with a horizontal binning factor of 2 and a vertical binning factor of 3 corresponds to 3 rows of 386 pixels each on the CCD chip. Examples of window definitions, and the resulting data frames, are given in §5 below.

 

DISPLAYING WINDOWS

The default location where OBSERVER looks for windows is given by the value of the logical name WINDOW_DIR, which is currently given by

WINDOW_DIR = ADAMLOCAL:[WINDOW.R0_0]
                           = ADAMLOCAL:[WINDOW.Q0_1A]
ADAMLOCAL = DISK$USER:[SYSDISK1.ADAMLOCAL.]

If you are logged in as OBSERVER or NIGHT then WINDOW_DIR will be defined. It is not defined if you are logged in as OBSRED.  Window files are sometimes also stored in DISK$USER:[OBSERVER], DISK$USER:[OBSERVER.WINDOW] and DISK$USER:[OBSRED], though OBSERVER must be given an explicit filename in order to read these files.

A called program PGWINDOW is provided to graphically examining these window files, when you log into the NIGHT account (your support astronomer will give you the password) on the VAX.  Before you can run it, you must set the DECW$DISPLAY logical name, using the xon script.

40a> xon aatxtr                       (replace aatxtr with the actual name
                         should be printed on the X-terminal or Sparc station)
40a> pgwindow

PROGRAM : WINDOW
Function -
To display the information contained in the .WINDOW files

PGPLOT v4.9G Copyright 1993 California Institute of Technology
Graphics device/type (? to see list, default xwindows): xwindows

Which detector [TEK]/GEC/THOMSON/RCA/UNKNOWN/quit ? TEK
What window file? (If your own specify disk as well as directory)
TEK1K_DIRECT_CEN

The ccd window you are using has been divided into
2 window(s).
--------------------------------------------------
Window number 1

this window is specified by the following pixels
X start X end Y start Y end
    366   665     366   665
X bin factor 1
Y bin factor 1
--------------------------------------------------
Window number 2
this window is specified by the following pixels
X start X end Y start Y end
  1029   1050  366     665
X bin factor 1
Y bin factor 1

As well as displaying the numerical values of the window, the program will display the window layout in a PGPLOT X-window, which should look like this example.


1.Vertical binning

Vertical binning means combining CCD rows. If the whole frame is to be binned in the same way, there is a single vertical binning field called the middle field. It is also possible to split the CCD window into two or three sub-windows (binning fields), with different binning factors.

If there are two vertical binning fields, the first is called the first  field and the second the middle field. These may have different  vertical binning factors.  If there are three vertical fields, they are called the first, middle and third  fields. The third field will have the same binning factor as the first.  The vertical binning field possibilities are:

Single vertical binning field
middle field binning factor n
 
Two vertical binning fields
first field binning factor n
middle field
binning factor m
 
Three vertical binning fields
first field binning factor n
middle
field & binning factor m
last
field binning factor n

2.Horizontal binning

Horizontal binning means combining CCD columns. If there is only one horizontal field in the window, it is called the centre field

If there are two horizontal fields, the first is called the left field and the second the centre field - this may have a different horizontal binning factor from the left field.

If there are three horizontal fields, the first field is called the left field, the second is called the centre field and the third is called the right field.  The right field will have the same horizontal binning factor as the left field. Thus for each window, there are three possibilities for horizontal binning:

Single horizontal binning field
centre field binning factor p
 
Two horizontal binning fields
left field binning factor p
centre field binning factor q
 
Three horizontal binning fields
left field binning factor p
centre field binning factor q
right field binning factor p

3.Window positions

Each window is positioned horizontally by specifying the number of pixels after the reference column. This number is allowed to be negative by a small amount.  DO NOT OVERLAP THE WINDOWS, since the software cannot cope with this.

The reference column is nominally the ``left'' edge of the chip, and is column 1 for all GEC CCDs (i.e.\ the first data column). For the RCA chip, there is currently an error of 8 columns, because the extension of the readout register is three pixels rather than eleven for the GEC chips. This will be corrected in a future version of the microcode by allowing the readout register overhang to be specified by a hardware command.) For now, the reference column for the RCA chip is column -7, where column 1 is again the first data column.

Both windows must start at the same row, and the vertical position is  specified by the number of pixel lines after the reference line  (which is always the first row of the chip, i.e. line 1).

 

 

 

 

 

 

 

 

 

 

 

4.Window parameters 

The following tables show the definitions of the `parameters' used in window definition files

 
Vertical Parameters
CCD-LTW Lines to window. (0 = nominal start of CCD chip)
CCD-NVF Number of vertical fields. (1 , 2 or 3)
CCD-LPBM Lines per bin in middle or only field
CCD-NBMF Number of image (data) rows in middle or only field
CCD-LPBF Lines per bin in the first field of two or three fields
CCD-NBFF Number of image (data) rows in the first field of 2 or 3
Left Window Horizontal Parameters
CCD-PTLW Pixels to left (first) window. (0 = nominal edge)           
CCD-NFLW Number of fields in left window. (1, 2 or 3)
CCD-BCLW Number of bins in centre or only field of left window
CCD-PCLW Pixels per bin in centre or only field of left window
CCD-BLLW Number of bins in left field of left window
CCD-PLLW Pixels per bin in left field of left window
CCD-BRLW Number of bins in right field of left window
Right Window Horizontal Parameters
CCD-PTRW Pixels to right (second) window                                     
CCD-NFRW Number of fields in right window
CCD-BCRW Number of bins in centre or only field of right window
CCD-PCRW Pixels per bin in centre or only field of right window
CCD-BLRW Number of bins in left field of right window
CCD-PLRW Pixels per bin in left field of right window
CCD-BRRW Number of bins in right field of right window

 

5.File layout & Examples

The window should be defined in an ASCII file with extension  .WINDOW. The default locations are the directories pointed to by the logical name WINDOWS_DIR (see above).  The general layout of existing (successful) definition files should be  followed. See the examples below, and note that the numeric fields of the .WINDOW files end in column 30.

5.1.  FORS.WINDOW

CCD-WINS= 'FORS    '                    / WINDOW NAME
CCD-LTW =                   -8          / LINES TO WINDOW
CCD-NVF =                    1          / NUMBER OF VERTICAL FIELDS
CCD-NBFM=                  584          / NUMBER OF BINS IN MIDDLE FIELD
CCD-LPBM=                    1          / LINES PER BIN IN MIDDLE FIELD
CCD-PTLW=                   -1          / PIXELS TO LEFT WINDOW
CCD-NFLW=                    1          / NUMBER OF FIELDS IN LEFT WINDOW
CCD-BCLW=                    1          / NO. OF BINS IN C. FIELD OF L. WNDW
CCD-PCLW=                    1          / PIXELS PER BIN CENTER FIELD L. WNDW
CCD-PTRW=                   74          / PIXELS TO RIGHT WINDOW
CCD-NFRW=                    1          / NUMBER OF FIELDS IN RIGHT WINDOW
CCD-BCRW=                  256          / NO. OF BINS IN C. FIELD OF R. WNDW
CCD-PCRW=                    1          / PIXELS PER BIN C. FIELD R. WNDW
END  

The final data frame recorded on disk will contain 256 columns x 584 rows. Rows 1-8 sample the bias overscan region. The figure below shows the location of this window on the GEC chip. Note that windows for the GEC chip start at column PTLW or PTRW +1.

5.2.  RCA_STAN.WINDOW

CCD-WINS= 'RCA_STAN    '                / RCA CHIP - STANDARDS AREA
CCD-LTW =                  171          / LINES TO WINDOW
CCD-NVF =                    1          / NUMBER OF VERTICAL FIELDS
CCD-NBFM=                  170          / NUMBER OF BINS IN MIDDLE FIELD
CCD-LPBM=                    1          / LINES PER BIN IN MIDDLE FIELD
CCD-PTLW=                   92          / PIXELS TO LEFT WINDOW
CCD-NFLW=                    1          / NUMBER OF FIELDS IN LEFT WINDOW
CCD-BCLW=                  170          / NO. OF BINS IN C. FIELD OF L. WNDW
CCD-PCLW=                    1          / PIXELS PER BIN CENTER FIELD L. WNDW
CCD-PTRW=                  319          / PIXELS TO RIGHT WINDOW
CCD-NFRW=                    1          / NUMBER OF FIELDS IN RIGHT WINDOW
CCD-BCRW=                   30          / NO. OF BINS IN C. FIELD OF R. WNDW
CCD-PCRW=                    1          / PIXELS PER BIN C. FIELD R. WNDW
END                     

This is a double window, used for observing standard stars when imaging with the RCA CCD. The left window covers 170 x 170 pixels near the centre of the chip, while the right window covers the bias overscan region. The final data frame will have 200 columns x 170 rows, with the data in columns 1-170. The starting column on the RCA chip is currently defined as PTLW or PTRW + 9.

5.3. GEC17-PAIR2.WINDOW

CCD-WINS= 'GEC17-PAIR2 '                / WINDOW NAME
LTW     =                   -8          / LINES TO WINDOW
NFL     =                    1          / NUMBER OF VERTICAL FIELDS
NBFM    =                  584          / NUMBER OF BINS IN MIDDLE FIELD
LPBM    =                    1          / LINES PER BIN IN MIDDLE FIELD
PTLW    =                  160          / PIXELS TO LEFT WINDOW
NFLW    =                    1          / NUMBER OF FIELDS IN LEFT WINDOW
NBFCLW  =                   10          / NO. OF BINS IN C. FIELD OF L. WNDW
PPBCLW  =                    2          / PIXELS PER BIN CENTER FIELD L. WNDW
PTRW    =                  210          / PIXELS TO RIGHT WINDOW
NFRW    =                    1          / NUMBER OF FIELDS IN RIGHT WINDOW
NBFCRW  =                   10          / NO. OF BINS IN C. FIELD OF R. WNDW
PPBCRW  =                    2          / PIXELS PER BIN C. FIELD R. WNDW
END         

This defines a pair of windows on the GEC chip, with the data double-binned in columns in each window. The final data frame will have 20 columns x 584 rows, where rows 9-584 have useful data and rows 1-8 sample the bias overscan region. Columns 1-10 have data from the left window and columns 11-20 data from the right window.

5.4. TEK1K_DIRECT.WINDOW

CCD-WINS= 'TEK1K_DIRECT'                / Window name.
CCD-LTW = 0 / CCD chip lines to window 
CCD-NVF = 1 / Number of vertical binning fields 
CCD-LPBM= 1 / No vertical binning 
CCD-NBFM= 1024 / Number of rows 
CCD-PTLW= 0 / CCD pixels to left window 
CCD-NFLW= 1 / No. horiz. binning fields in L.window 
CCD-PCLW= 1 / No horizontal binning in left window 
CCD-BCLW= 1028 / Number of columns in left window 
CCD-PTRW= 1028 / CCD pixels to right window 
CCD-NFRW= 1 / No. horiz. binning fields in R.window 
CCD-PCRW= 1 / No horizontal binning in right window 
CCD-BCRW= 22 / Number of columns in right window 
END 

A full sized window  (1028x1024) with a bias overscan (22x1024)


 
 
 
 
 
 
 
 
 

5.5. TEK1K_DIRECT_CEN

CCD-WINS= 'TEK1K_DIRECT_CEN'            / Window name.
CCD-LTW =                  365          / CCD chip lines to window              
CCD-NVF =                    1          / Number of vertical binning fields     
CCD-LPBM=                    1          / No vertical binning                   
CCD-NBFM=                  300          / Number of rows                        
CCD-PTLW=                  365          / CCD pixels to left window             
CCD-NFLW=                    1          / No. horiz. binning fields in L.window 
CCD-PCLW=                    1          / No horizontal binning in left window  
CCD-BCLW=                  300          / Number of columns in left window      
CCD-PTRW=                 1028          / CCD pixels to right window            
CCD-NFRW=                    1          / No. horiz. binning fields in R.window 
CCD-PCRW=                    1          / No horizontal binning in right window 
CCD-BCRW=                   22          / Number of columns in right window     
END

A 300x300 pixel window in the centre of the TEK CCD, with a 22x300 pixel bias overscan


 
 
 
 
 
 
 
 
 

5.6. TEK1K_CEN_100

CCD-WINS= 'TEK1K_CEN_100'               / Window name.
CCD-LTW = 450 / CCD chip lines to window 
CCD-NVF = 1 / Number of vertical binning fields 
CCD-LPBM= 1 / No vertical binning 
CCD-NBFM= 100 / Number of rows 
CCD-PTLW= 450 / CCD pixels to left window 
CCD-NFLW= 1 / No. horiz. binning fields in L.window 
CCD-PCLW= 1 / No horizontal binning in left window 
CCD-BCLW= 100 / Number of columns in left window 
CCD-PTRW= 1028 / CCD pixels to right window 
CCD-NFRW= 1 / No. horiz. binning fields in R.window 
CCD-PCRW= 1 / No horizontal binning in right window 
CCD-BCRW= 0 / Number of columns in right window 
END 

A 100x100 pixel window in the centre of the TEK chip, with a 1x100 pixel overscan.


 
 
 
 
 
 
 
 
 

5.7. THOMSON_F1

CCD-WINS= 'THOMSON_F1'                 / Window name.
CCD-LTW =                    0          / CCD chip lines to window              
CCD-NVF =                    1          / Number of vertical binning fields     
CCD-LPBM=                    1          / No vertical binning                   
CCD-NBFM=                 1024          / Number of rows                        
CCD-PTLW=                    0          / CCD pixels to left window             
CCD-NFLW=                    1          / No. horiz. binning fields in L.window 
CCD-PCLW=                    1          / No horizontal binning in left window  
CCD-BCLW=                 1024          / Number of columns in left window      
CCD-PTRW=                 1024          / CCD pixels to right window            
CCD-NFRW=                    1          / No. horiz. binning fields in R.window 
CCD-PCRW=                    1          / No horizontal binning in right window 
CCD-BCRW=                   40          / Number of columns in right window     
END

A 1024x1024 pixel window (the ful chip) and a 40x1024 pixel overscan region


 
 
 
 
 
 
 
 
 

5.8. THOMSON_F1_CENTRE

CCD-WINS= 'THOMSON_F1_CENTRE'           / Window name.
CCD-LTW =                  363          / CCD chip lines to window              
CCD-NVF =                    1          / Number of vertical binning fields     
CCD-LPBM=                    1          / No vertical binning                   
CCD-NBFM=                  300          / Number of rows                        
CCD-PTLW=                  363          / CCD pixels to left window             
CCD-NFLW=                    1          / No. horiz. binning fields in L.window 
CCD-PCLW=                    1          / No horizontal binning in left window  
CCD-BCLW=                  300          / Number of columns in left window      
CCD-PTRW=                 1024          / CCD pixels to right window            
CCD-NFRW=                    1          / No. horiz. binning fields in R.window 
CCD-PCRW=                    1          / No horizontal binning in right window 
CCD-BCRW=                   40          / Number of columns in right window     
END

A 300x300 pixel window centred in the centre of the chip, with a 40x300 pixel overscan region.


 
 
 
 
 
 
 
 
 

5.9. THOMSON_BIN2

CCD-WINS= 'THOMSON_BIN2'                / Window name.
CCD-LTW = 1 / CCD chip lines to window 
CCD-NVF = 1 / Number of vertical binning fields 
CCD-LPBM= 2 / Vertical binning factor 
CCD-NBFM= 512 / Number of (binned) rows 
CCD-PTLW= 7 / CCD pixels to left window 
CCD-NFLW= 1 / No. horiz. binning fields in L.window 
CCD-PCLW= 2 / Horizontal binning factor - left windo 
CCD-BCLW= 1 / Number of binned columns in left windo 
CCD-PTRW= 9 / CCD pixels to right window 
CCD-NFRW= 1 / No. horiz. binning fields in R.window 
CCD-PCRW= 2 / Horizontal binning factor - right wind 
CCD-BCRW= 511 / Number of binned columns in right wind 
END 

A  512x512 bin window (binned in X and Y - 2 pixels per bin), offset by 8 pixels in the X direction.


 
 
 
 
 
 
 
 
 

5.10 THOMSON_F1_TEST.WINDOW

CCD-WINS= 'THOMSON_F1_TEST'             / Window name.
CCD-LTW =                    0          / CCD chip lines to window              
CCD-NVF =                    1          / Number of vertical binning fields     
CCD-LPBM=                    1          / No vertical binning                   
CCD-NBFM=                 1024          / Number of rows                        
CCD-PTLW=                  500          / CCD pixels to left window             
CCD-NFLW=                    1          / No. horiz. binning fields in L.window 
CCD-PCLW=                    1          / No horizontal binning in left window  
CCD-BCLW=                   10          / Number of columns in left window      
CCD-PTRW=                  510          / CCD pixels to right window            
CCD-NFRW=                    1          / No. horiz. binning fields in R.window 
CCD-PCRW=                    1          / No horizontal binning in right window 
CCD-BCRW=                    1          / Number of columns in right window     
END

This 10 x 1024 pixel window is for making short test observations with the Thomson CCD. Its usual shape prevents the `fast readout' mode from saturating the readout register (by binning many otherwise unsaturated pixels into the readout register). Use it to test levels of flat field exposures.

6.Time-Series Exposures and Windows

Time Series Mode is a special CCD readout mode which uses charge sguffling techniques to continuously observe with and read from an AAO CCD, to create a data cube with a time axis. It is mostly used for spectroscopy. A discussion of its use on the RGO can be found in the RGO Manual Section 6.3.

 


Introduction The Telescope & Optics The Detectors
The Imaging Cameras An Imaging Cookbook The Data you Take Away
Exposure times OFFSET_RUN files CCD Windows Data Catalogs
On-line Reduction Filters Flat-fields Blank Fields Orientation Shutters

Back Contents Next

Last Contents Next

This Page maintained by : Chris Tinney (cgt@aaoepp.aao.gov.au)
This Page last updated:  8 Mar 1996, by Chris Tinney