When you take an exposure with INGRID the array is reset and immediately read out. This is called the pre-read image, and is stored in extention 1 of the file (rxxxxxx.fit[*,*,1]). After the exposure time has passed the array is read out again. This is called the post-read image and is stored to the extention 2 of file (rxxxxxx.fit[*,*,2]). The information useful for the observer is the difference between these two images. The ingrid_ql package provides a quick way to access this information.

This package, its documentation and the information given here have been created by Robert Greimel.

Concerning data reduction, James Geach has created his own INGRID data reduction pipeline and has kindly made it available to other INGRID users. Click here for further info.

• Open an ximtool (or another display tool) to display the data (i.e. type ximtool& or ds9&, for example).

• Start an IRAF session: open an xgterm, change to the home directory and type cl (or ncl). The prompt will change to cl>

• Type: cl> ingrid_ql. The prompt will change to in>

• Type: in>help usage, to get information about the use of the package

• Type: in>help to get a list of the available tasks.

• Type: in>help task_name to get more information on using each particular task.

Some of the most frequently used tasks are:

idedither	combine dithered images
idispframe	display frame (post-pre)
istarfocus	find focus from focusrun images
icombine	combine images
ifindron	find readout noise from two dark frames
iframediff	calculate and store post-pre
ilistdark	list dark exposure times needed
istatistics	calculate image statistics
isubtract	subtract two images

You can also download the INGRID quick look package and install it for your personal use. The information is given here.

• istarfocus can then be used to find the best focus values from the stars visible in this image. For example, if you took a focus series of 9 exposures with variable telescope focus you would then find the best focus with the following command:

  in> istarfocus r554443 nim=9

  The process to focus the telescope is also described in the INGRID users guide.

• idispframe

  Once you have taken an exposure you probably want to view it. To view an image use the idispframe task. For example:

  in>idisp r123456 1
  

  will display exposure number 123456 in frame 1 of your display tool. You can then use imexamine to examine this image as usual. All parameters for the display are also available for idispframe. Additionally if you want to subtract a sky frame from before displaying the image you can use the parameters subsky and sky.

  in>idisp r123456 1 subsky+ sky=sky_h
  

  would subtract the image "sky_h" from "r123456" before displaying. A quick and dirty way to subtract a sky image is to use an exposure from a different field as the sky image, for example:

  in>idisp r123456 1 subsky+ sky=r123455
  

• idedither

  This is another commonly used task. If you have taken a dither this tasks combines the images. You can select one of three methods with the match switch to find the offsets for combining the images:

  • match="wcs" This is the most automatic way. The wcs, generated from the telescope pointing information, is used to find the offsets between images.

  • match="pick1" This method is half automatic. The first image is displayed and you should pick a star with the 'm' key that will be visible on every following image. The task then calculates where the star should be on any image from the telescope pointing information and uses imcentroid to get the exact offset.
    
  • match="manual" This method is completely manual. Every image is displayed and you have to pick the same star on every image. The positions of the stars are then refined using imcentroid and used for calculating the image offsets.

    To reassemble a 5 point dither using the "pick1" method and storing the result in a file named "comb" use:

  in>idedither r123456,r123457,r123458,r123459,r123460 comb match="pick1"

  Of course you can also use lists to specify the input files. The following example would combine all files listed (one file per line) in the file allfiles using the telescope pointing information and put the output into a file named "allcomb":

  in>idedither @allfiles allcomb match="wcs"

Back to INGRID Homepage

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Last Updated: 5 August 2001 A. Zurita azurita@ing.iac.es