Menu Bar Options

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File

Load FITS

Launches a dialog box that allows you to choose a FITS file, specifying:

• FITS extension
• column list
• Whether to auto-scale the data (this affects the displayed colours but not the image values themselves). If you select this option you can choose to plot the histograms used to find the mode.
• a label for the tab, used as a prefix for the column label in the fits file, if any. (If not specified, a label is constructed based on the FITS header which tries to distinguish the new tabs from those previously loaded.)

If autoscale is not selected, after the file has been opened, Ximview launches the Adjust scaling dialog box. To display the full range on each newly-loaded image, clear the "range" text box and click Accept. To set all images to the same scale, choose the settings you want and click accept. Otherwise, click Clear tab choice then select one image, choose the settings, Accept. The dialog re-appears until scales are set for all the images.

Load image file

Reads an image file in any of the formats known to IDL, e.g. PNG, BMP etc. NB: as with Load FITS, the image must have the same size as the currently-loaded images. As a result, this option is not very useful but is included for development purposes.

New logfile

Starts a new log file. The choices are to:

• overwrite the old log file
• make a file with a new sequence number, i.e. named "ximview_n.log" where n is a unique number
• Named...: you specify a filename via a pop-up box.

Write PNG

Dumps the currently-visible image area and scale bar to a PNG file. A pop-up requests the file name.

NB under DirectColor the output image will be greyscale.

Reset

Makes the image window sensitive to cursor motions and re-enables panning, in case either of these have been turned off accidentally.

Exit

Ends Ximview.

Display

Adjust Scaling

Launches a dialog box that allows you to change all the scaling options:

Choose Tabs

If there are multiple tabs, check the boxes for the tabs you want to adjust.

Make current

Check the box for one tab to set the input values (and values for info such as the full data range) to those currently set for this tab.

Colour table

Choose from the list. If Colour handling is set to "Same for all" (the default), this will be applied to all tabs (excluding RGB tabs), unlike the other options. See below for comments on each table.

Transfer Function

Choose from the list of transfer functions.

Wrap colour table?

No

image intensities outside the range set in Data range for scaling are displayed as the minimum or maximum colour.

Full

gives a cyclic mapping between image intensity and TV colour: pixels with intensities within the scaling range are unaffected, but pixels outside the range map to a (multiply) cycled colour instead of saturating.

Bright end only

as for Full but only for intensities above the maximum of the scaling range. (Recommended).

Full data range

For information. The units used here are adjusted to scale the image maximum intensity into the range [1, 1000) units, e.g. if the peak on the map is 0.123 K it will be reported as 123. mK. Specify the range in the same units (mK in this case).

Mode and Estimated rms

For information. Same units as the data range. These values are only available if auto-scale has been run.

Plot histogram on autoscale?

If this box is checked before auto-scale is run, a histogram of the values around zero is shown with the derived mode marked (also the parabolic fit used to derive the mode). This allows you to check that the value is sensible.

Data range for scaling

Specify the image intensities that map to the faintest and brightest displayed colours (excluding wrapping).

Beta for Asinh scaling

Sets the break between quasi-linear and quasi- logarithmic scaling (see transfer functions).

Effective zero level

Set to your best guess of the image intensity level corresponding to true zero. The reported values are not altered, but this is used by the Asinh scaling function, the red-black-blue colour scale, and the preserve colour option for RGB images.

Along the bottom of the box are the following buttons:

Clear tab choice

Unsets all the tab selection checkboxes.

Autoscale

Applies the auto-scale algorithm to the "current" image. The other tabs are automatically unselected as a reminder that the values returned depend on the particular image. The image is not scaled right away; instead the suggested values of the data range, zero level and β are filled in (along with the Full data range, mode, and rms if not previously set).

Note: this may take a few seconds the first time it is run. It is quicker to auto-scale HEALPix maps on input.

The suggested values will be overwritten if you make another tab current, but can be recovered instantly by clicking Autoscale a second time.

Accept

Applies the chosen scaling parameters to the selected tabs.

Cancel

Don't change any scaling (but the full data range, mode, and rms are recorded if auto-scale has been run).

Auto-scale all tabs

Each image is auto-scaled. It just goes ahead and applies the scaling, there is no request for confirmation.

Colour table

Select your prefered colour table:

Rainbow

Default on startup. Garish but gives good discrimination between levels.

Heat

Black-red-orange-white. Rather low contrast

Blue-yellow-white

Supposed to be a "colour-blind friendly" scale in that it should look the same to the 5-10% of the male population with red-green colour-blindness.

Greyscale

Actually gives better contrast than "Heat", especially at low intensities.

Red-black-blue

Designed for images where the signal may have either sign, e.g. Stokes parameters Q, U, and V, velocity maps, or CMB maps. The intensity that maps to the zero level is set to black, negative intensities are coded red to white, and positive intensities are coded blue to white. The scaling to white is the same on both sides, so if the range is lopsided, e.g. −1 to 10, only one side will reach white.

Cyclic

Constant saturation and intensity and hue cycling through 360°. Suitable for displaying phase or polarization angle.

Colour handling

Choose:

• Same for all: (Default) Same colour scale for all tabs, except tabs displaying 3-colour images (RGB or HSV), which always have their own scale. NB: For TrueColor displays this requires re-drawing all screens when the scale is changed, which may take a few seconds.
• Separate on each tab: Each tab has its own colour table.

Set view centre

Enter the position for the view centre in one of the following systems:

• image pixels (x and y pixel coordinates)
• HEALPix pixel number in either RING or NESTED order.
• Longitude and latitude in degrees (in the native coordinate system of the image).

The view centre is defined as being the centre of a a pixel. You get the nearest pixel to the demanded position.

Long/Lat is not yet enabled for butterfly projections.

Restore default screen size

Returns the Ximview window to its initial size (512 × 512 pixel image window).

Tabs

Blink Setup

Launches a dialog box with a checkbox matrix allowing you to specify which tab appears at which point in the sequence. The matrix can be cleared with the Clear sequence button.

You can also specific the blink period (per tab, not total) in seconds, and choose to omit the scale bar, which can be distracting if it differs between images.

Click the Done button to start blinking immediately. Otherwise click Cancel.

Red-Green-Blue

Launches a dialog box with a checkbox matrix allowing you to assign any images already loaded to the red, green and blue channels of a new image (a new tab is created for it). Two colour scaling options are available:

Saturate to white

objects that are saturated (ie displaying the maximum colour value) in all three channels will display as white. In this case the intensity scaling for each channel is unchanged when the RGB image is created. If the scaling of any channel is changed on the original tab, the RGB image will change to match, but only when the underlying pixmap is updated, e.g. on a change of zoom or significant panning. In the latter case the RGB image may be updated in some regions but not others, leading to odd-looking results.

Preserve colour for saturated pixels

uses the SDSS algorithm of Lupton et al. (2004), see Preserve colour.

Polarization

Options for displaying polarization information based on images already loaded. A dialog box allows you to select two channels representing one pair of

1. Stokes parameters Q and U
2. Polarized intensity and angle
3. Fractional polarization and angle.

In each case you can also choose a third channel representing total intensity (Stokes I).

At present there is only one option:

Colour

Makes a new tab. For two channels you get a Hue-Value (HV) image where hue (colour) represents polarization angle and value (brightness) represents polarized intensity (or fractional polarization for option 3).

For three channels you get a hue-saturation-value (HSV) plot where hue is angle, saturation is fractional polarization and value is Stokes I. Saturation is a linear scaling of fractional polarization from zero to a maximum you set in the dialog box. For both HV and HSV the channel mapped to "value" uses the same scaling as already set on its original tab, if available. For option (1) HV plots, the value (pol intensity) is calculated on the fly and you get linear scaling from zero to a maximum set in the dialog box.

Delete tab

Delete current tab

does just that, right away.

Specify

select from a list (includes a cancel option).

Analysis

Imstats

Box

Select to use a square or rectangular box around the marked point to define the region for statistical analysis (Default).

Region of interest

Select the region to analyse using the IDL CW_DEFROI routine: options of polygon, point, rectangle and circle. Several such regions can be defined before finishing; the union of all will be used. NB: the position readout on the CW_DEFROI window is meaningless (but the readout on the Ximview window works as usual).

Set box size

in pixels. Enter one number for a square box, two for a rectangle.

Peakfit

Find extremum

Default. Finds the largest maximum or minimum in the search box.

Find maximum

Does that, ignores minima.

Find minimum

Does that, ignores maxima.

Set box size

Enter size of square box in pixels.

Clear mark

Unsets the current marked point and removes the graphics marker.

Set image properties

A dialog box allows you to select a tab, see the current value of the property in question, and set a new value. These properties are used to check for image compatibility for certain options, currently only polarization display.

Polarization

You can choose from a list of possible polarization products.

Frequency

You can choose from the list of frequencies already loaded, or enter a new value. The value is a text string, e.g. "K band" "408 MHz" etc.

Help

Help

Launches this help browser, or displays a plain text version in IDL versions before 6.2.

Release Notes

Displays list of changes for each version of Ximview.

About

Displays Ximview credits.