User's Guide to IRCAL

Table of Contents

Summary Table
Quick start
Instrument Characteristics
Software Overview
Data File Info
Filters, Grisms, Polarimeter
Nodding and Dithering Scripts
Observing Procedures and Tips
Technical Details

Mt. Hamilton Homepage

IRCAL Image Display - ircaldisplay

ircaldisplay is a Tcl/Tk wrapper around and IDL gui that creates four windows upon startup: ircaldisp, Image Browser, Radial Profile, and Foc Fit.

ircaldisp | Image Browser | Radial Profile | Foc Fit


Click for a full-sized image.

The ircaldisp window will, by default, automatically display the most recent IRCAL exposure. File and Object names are displayed at the top of the window. If the fwhm calculator is selected in the Image Browser, the Strehl measurement will be displayed next to the filename.

The File menu has two options: Show Header and ReadFits. Show Header will display the FITS header for the currently displayed image. ReadFits will let you select and display any FITS file.

The ColorMap menu has a selection of color maps for the display: Default, Grayscale, Stern Special, and Red Temperature. Any IDL colormap can be loaded with the XLoadCT option.

The Axes menu allows you to choose either No Axes, Pixels, or Arcseconds for the displayed images axes.

The Scaling menu allows you to change the scaling of the image display. Choices are, Full Range, Min Max, Log, SigDisp, SigDisp (zoomed region only), and HistEq. HistEq is histogram equilisation of the image. SigDisp displays 1 sigma around the mean of the image. If you wish do display a different sigma around the mean (e.g. 12 sigma) you can do that through the Image Browser window.

Below the image display is a readout of the x-y position and pixel value of the cursor position.

There are three modes of interacting with the image display: Recenter, Zoom, and Unzoom. Recenter will put the clicked pixel at the center of the image display. Zoom will zoom in around the clicked pixel. Unzoom will zoom out around the clicked pixel.

The FullImage button will display the full image in the gui.

Image Browser

Click for a full-sized image.

Radial Profile Plot from FWHM calculator
Click for a full-sized image.

This is the main window for image display and manipulation. Labeled buttons perform that function when pressed. The radio buttons to the left of the labeled buttons determine which functions are automatically done when a new image is displayed. Radio buttons that are on are depressed and red in color.

The newest button at the top of the window will display the most recent IRCAL image. In the parentheses will be the most recent image number or unknown if no image has been taken since ircaldisplay was started.

The Display Image # button allows you display the image of your choice. Enter the desired image number in the box to the right. You may also increment or decrement the image number to be displayed by using the up and down arrows on the right.

The Subtract Image # button enables the subtraction of an image from the displayed image. Enter the desired image number to be subtracted in the box to the right. You may also increment or decrement the image number to be subtracted by using the up and down arrows on the right.

The full range button displays the current image over the entire range of pixel values, scaling the color map accordingly.

The sigdisp button displays the current image over a range of pixel values x sigma around the mean. Default is 12 sigma, but can be changed in the box to the right. Commonly used values are 1, 3, and 5 sigma in addition to the default.

The minmax button displays the current image over the range of pixels specified in the boxes to the right.

The stats button displays the mean and standard deviation of the image pixel values.

The fwhm button calculates the FWHM, centroid, and estimates the Strehl of a source in the image. The measurements are displayed in the xterm window from which you started ircaldisplay in following format (for example):

  xcen  ycen     peak(g/r)      xfwhm yfwhm npfwhm 
  128.3 125.6   8495. /  8319.   1.84  1.79  2.09  

  flux    sky      strehl
 65544.     3.0  0.80 / 0.78
The x and y centroid from a gaussian fit of the object are xcen and ycen.
The peak flux of the source is calculated two ways: the peak of the gaussian fit (g) and the measured peak of the object (r).
xfwhm and yfwhm are the x and y FWHM calculated from a gaussian fit to the object.
npfwhm is the FWHM calculated directly from the number of pixels above half the peak value.
The total flux of the star is total (sky subtracted) counts inside the photometry aperture.
The sky flux displayed is the average per pixel as measured in the sky aperture.
The estimated Strehl is calculated two ways, based on the two peak measurements: Strehl=peak/flux/0.162. Note that this Strehl is only a valid approximation when using the K-band filter.

In automatic mode, the algorithm finds the FWHM around the peak pixel in the image (note: sometimes this will find a bad pixel or cosmic ray, not a real object). In manual mode you will click on the fwhm button then click on the source in the image. Two circles will be overlaid on the image around the source, one showing the FWHM fitting region and another for the photometry calculation region. The radii for these two functions can be set using the Image Browser - Config - Configure menu (see below). The radial profile and FWHM fit will be displayed in the Radial Profile window. Please note that the Strehl calculation is only accurate for K-band images.

The Move Tel button allows you to move the telescope by clicking on the image. This is particularly useful for positioning an object on the array. Click on Move Tel, then click on the object, then click the position you wish to object to be. The telescope should move the proper distance and direction to put the target on the desired position on the chip.

The two IDL buttons allow IDL commands to be executed. Enter the command in the dialog box and press the IDL button to send it. The currently displayed image is called img in the IDL session and you can manipulate the image using regular IDL commands.

The reset IDL button sends an IDL retall command in case the Image Browser gives an IDL error or gets confused on which display window is which. This is a good general fix to most problems that the Image Browser occasionally exhibits.

The hardcopy button sends the currently displayed image in the ircaldisplay window to the shane printer in the 3-m control room.

The focfit, focval, and focfit init are used for focusing IRCAL and image sharpening. The focfit program fits a parabola to the Strehl of each image at various focus values and prints the best focus value. In addition, focfit displays a zoomed view of the image around the point source being measured. The focval entry box is the focus (or image sharpening mode) value. The focfit init button initializes the focus fitting program using the focval entry and Strehl of the current image as the first data point. The focfit button adds new data points (Strehl and focval entry) to the parabola fitting program. The following procedure is typically used for focusing IRCAL with focfit:

  1. Determine the proper exposure time so that the white light internal calibration source does not saturate IRCAL, but still gives high signal-to-noise. Typically one uses the Br-Gamma filter.
  2. Check the auto fwhm checkbox in the image browser window.
  3. Take an exposure with IRCAL.
  4. Enter the current IRCAL focus position in the focval entrybox.
  5. Push the focfit init button.
  6. Change IRCAL focus (IRCamFocus window in AO software)
  7. Take an exposure with IRCAL.
  8. Enter the current IRCAL focus position in the focval entrybox.
  9. Push the focfit button.
  10. Repeat previous 4 steps until you get a good focus. After 3 focus positions a plot will be displayed in the IDL 31 window and the best focus estimate will be printed.
Use a similar procedure for image sharpening to get the best possible strehl and internal alignment.

Image Browser - Config Menu

Click for full-sized image.

The Config menu has two selections: Configure and Update newest file. Update newest file simply looks in the current data directory for the most recent file and displays it. Configure brings up a window where you can change the data path, the parameters (fwhm radius and photometry radii) for the FWHM/Strehl estimating routine, and if the new image always zooms to fill the display window.

Elinor Gates
Last modified: Thu Mar 1 10:09:05 PST 2007