FITSview

Please send any comments and/or suggestions to Bill Cotton (bcotton@nrao.edu)

     This program is a viewer for astronomical images in FITS (Flexible Image transport System) format.  An image can be displayed in a number of ways including colorizing the display, zoom and scroll, etc.  In addition, celestial positions (WCS, IRAF and DSS) can be determined for locations in the image by clicking the left mouse button when the cursor is over the desired feature.  Either normal FITS images or FITS images which have been compressed using the gzip compression  (*.gz) may be read.

   The FITSview Home page is http://www.cv.nrao.edu/~bcotton/fitsview.html.


Overview

This viewer will display and manipulate astronomical images in FITS format or FITS format images which have been compressed using the gzip compression technique.  The file to view can be specified as a command line argument or using the Open item in the File menu.  Subsequent files can also be selected using the Open function.   Information about the displayed image can be obtained using the Image info item in the File menu.

   The header of a FITS file (or the text of a text file) may be previewed before deciding which image to load.  Once a file is displayed it can be manipulated and examined in a number of ways.  If the image is larger than the display, the scroll bars on the edge of the display will scroll around inside of the image.  Clicking the left mouse button in the display will result in the brightness and celestial position of the pixel under the cursor being displayed at the bottom of the Display control box.  A click on the right mouse button is similar except that a point model is fitted to the image near the selected pixel; the results are given in the Display control box.  These brightness and position displays can be logged to a text file by selecting the "Log positions" option in the file menu.

   Standard World Coordinate System (WCS) coordinates are supported as well as the astrometric plate parameters from the Digitized Sky Survey (DSS) and the IRAF CD matrix. Positions can be displayed in either equinox B1950 or J2000 if the equinox given in the image is either of these.

   The brightness and contrast of the image can be adjusted using the horizontal scroll bars  at the top of the Display control box.  Moving the slider to the right will increase the contrast or the brightness.  If the range of pixel brightness  of the portion of the image of interest is significantly smaller than the total range, contrast and brightness adjustments may be insufficient.  In this case, a limited range of pixel values can be displayed using the Pixel Range dialog box in the Options menu,  Alternately, the nonlinear option in the Options menu may display the desired range of brightness.  Blanked pixels always appear as black.

   The image can be displayed in color using one of two color schemes, Color Contour and Pseudo Flame in the Colorize menu.  Color Contour is an 8 color scheme  which gives a contouring effect and Pseudo Flame is a continuous color pseudo coloring scheme. giving the image a flame like quality.  Option Grayscale is a black and white coloring scheme.  The order of the color table (black becomes white etc.) is reversed using the Reverse item.   Brightness and contract controls also work on colorized images.  The color, contrast and brightness can be reset using the Reset item on the Colorize menu.

   When an image is initially loaded, generally the first plane in the file is displayed.  If the image contains multiple frequency or polarization planes,  other planes can be loaded using the Set Plane dialog box in the Options window.  The number and type of planes in the file can be determined using the Image Info item in the File menu.  A cube can be displayed as a movie (using the "Movie" item in the Movie menu) to show a range of planes in sequence or by selecting planes at random.

   An image can be zoomed in or out using the Zoom menu and selecting the desired magnification factor.  Zooming in (factor > 100%) is done by replicating pixels and zooming out (magnification <100%)  by displaying only a subset of the pixels.  Zooming is centered on the current scroll position controlled by the image scroll bars.  Selecting a zoom factor of 100% undoes the effects of zooming.

   Celestial positions determined from mouse clicks can be refined using the Fit Point Model option in the Position menu.  This will fit an accurate position and flux assuming a point object near the position of the last mouse click.  The results will be displayed in the lower left corner.  Clicking the right mouse button will  give the same result. The Mark Position item in the Position menu will bring up a dialog box in which the celestial coordinates of an object of interest can be entered; alternately a list of positions can be given in a file.  The corresponding location(s) on the  image will be marked.

   Two images can be compared using the Blink facility controlled by the Blink menu.  Blinking will alternately display one image and then the other.  The first image is loaded into the display and desired adjustments are made.  It is then copied into the Blink image using the Copy to blink store item in the Blink menu.  The second image is then loaded into the display and adjusted as desired.  The Blink images item on the Blink menu will then begin blinking.  The dwell time on each image can be controlled using the scroll bar in the blink dialog box.  The Quit button on the dialog box ends blinking.   If the two images have pixels coincident on the sky, the zoom and scroll used are that for the current display (the one visible before the blink starts).  If the pixels are not aligned, blinking uses the scroll, zoom and display setup for the first image that were in effect when it was copied to the Blink image and the current setup for the second (normal display) image before the blink began.  The Swap current and blink item swaps the current and blink images.

   Once an image is loaded, its display can be written to a device independent bitmap (.BMP) format file.  This file will have the color, brightness and contrast of the current display but is unaffected by zoom and scroll.  This file may then be read into other programs.  The currently displayed portion of an image can be printed using the Print item in the File menu.


Celestial Position

Celestial positions on the sky are similar to latitude and longitude used to measure position on the earth.  A celestial position consists of a "Right Ascension", usually abreviated RA,  corresponding to longitude and a "Declination", abreviated Dec, corresponding to latitude.  Declination is measured in degrees north and south of the celestial equator, the projection of the earth's equator onto the sky.  Right Ascension is measured in time units, hours, minutes and seconds of sidereal time.

   The Earth's rotation axis wobbles with a 25,000 year period due to precession which causes the apparent position of a object to change with time.  Celestial positions are therefore usually expressed in terms of the earth's orientation at a set of standard times called Equinoxes.  At the current time two standard equinoxes are in common use, B1950 or the mean positions at the beginning of 1950 AD and J2000 or position in the year 2000.  The B and J refer to the different conventions used to precess (change the positions to another time) the coordinates.


Blinking

Blinking is a technique for comparing images.  If the pixels in two images are aligned and the two are repeatedly displayed one after another, the details of the two can be compared.


Zooming

   Zooming an image on a display gives the visual impression of getting closer or further from the objects.  In this program, zooming in is done by copying the pixels and zooming out by dropping pixels.  This technique either blows up a portion of the image for easier examination or increases the region of the image that can be shown at once on the display.


Color Table

   Image displays show images by representing the value of each pixel by a color or gray shade. The correspondence between the pixel values and the color displayed is called the color table.


Scrolling

     If an image is larger than the display only a portion can be seen at once.  Scrolling is the technique of moving the image is the display so that different parts are visible.


Pixel

   A pixel is a cell in an image; its value corresponds to the brightness of the image at that position.  In astronomical images a pixel corresponds to a location on the sky.  In images with more than 2 dimensions pixels are sometimes called voxels.


Image plane

   The simplest images consist of a single two dimensional array of  pixels.  An image may contain several (or many) of these 2-D arrays or planes.  Each of the planes can be displayed as an image.  These planes may represent the same region of the sky at different frequencies of light or in different polarization states of the light.


Precession

   Precession is the wobbling of the earth's rotation axis due to the gravational field of the sun and moon.  This effect is like the wobbling of a top as it slows down.  Earth's rotational axis takes about 25,000 years for each cycle.  Since celestial coordinates are changing with precession ,they are usually referred to a standard time or equinox.  Currently used equinoxes are B1950 (beginning of the year 1950 ) and J2000 (beginning of the year 2000).


Blanked pixels

      If an image has no measured value associated with a given pixel it is said to be blanked or invalid.


gzip compression

Compressed files

      Most images or text files are compressible in that their contents can be represented using much less disk space or memory.  There are several compression techniques in common usage but FITSview can read files compressed using the gnu compression (gzip) technique.  These file can be either viewed directly or decompressed using gunzip before viewing.  There is some performance penalty reading a compressed file as it must be decompressed on the fly but there can be substantial savings in disk storage space using compressed files.  Gzip compressed files frequently have ".gz" (or similar characters) as the last part of the file name but FITSview can recognize such files by their internal signature or "magic number".


 File Menu

This menu includes a number items related to files.  Files to be viewed using the Open function or previewed using the Preview function may be either regular FITS (or text) files or these files after compression by the gzip method.  These compressed files are usually indicated by a ".gz" at the end of the file name although this is not necessary.

   Individual menu Items are:

 Open

 Preview FITS header

 Save as FITS file

 Image information

 Print

 Save BMP

 Log Positions

 Exit


Open

   This item will bring up a file browser dialog box to select the FITS file to load.  When a file is loaded, the previous image is discarded.  The title bar of the main window gives the name of the currently loaded file.

   Note: the default extension of the FITS file is *.FIT; if the files have other names then the file mask needs to be set to *.* in the file dialog box.

   If the file is not a FITS image then error messages will be displayed in dialog boxes.  Click the OK button to continue and select a valid FITS image file.

   If the FITS header does not tell the maximum and minimum values in the image then FITSview reads throught the first plane to determine these values.  If no Pixel Range is specified (both values 0) then FITSview attempt so guess the appropriate range to display.

   When the file is being loaded to the display, a box appears with a progress message and a cancel button.  If the message "WARNING: BAD PIXEL RANGE" appears then all of the pixels loaded are at one extreme of the range of displayed brightness.  This usually indicates inappropriate values in the Set  Pixel Range option in the Options menu.  This may be the result of a previous image with a very different range of pixel values.  Setting both values to zero will get the default display.


Preview

   This item will display up to about 1000 lines of the header of a selected FITS file or text file in a scroll box.  This allows deciding which image to load or reading explanatory text.  The first line of the header of a FITS header is:

SIMPLE  =                     T     /possibly some comment

An FITS image file has a line near the beginning of the form:

NAXIS1   =              nnn        /possibly some comment

where nnn is an integer larger than 0.  The size of the image is given by the NAXIS1 and NAXIS2 entries.  Information about the image may be contained in HISTORY or COMMENT lines.


Save as

   This item will cause the currently displayed image to be written to a FITS file.  A file selection dialog box will pop up in which the desired name of the new file is to be entered.  The output file is in uncompressed form whether or not the input image is.


Image info

   This item will display information about the current image including positions, frequencies, observation dates, etc.  The dismiss button clears this display.


Print

   This item will print the currently displayed image.  The region of the image printed is that in the current display; a combination of zoom, scroll and resizing the window allows selecting an arbitrary region of the image.  The printed version gives information about the image and the location of the center and the size of the displayed region.


 Save BMP

   This item will cause the currently displayed image to be written to a device independent bitmap (BMP) format file.  A dialog box will allow selection of the directory and file name to be written.  The output file will have the color, contrast and brightness of the current display but is unaffected by scroll and zoom.


Log positions

   This will toggle the logging of brightness and position selected by a mouse button click or fitting a point model to the image.  When this is turned on, a dialog box will allow selection of the text file.  The logging file contains one line per position containing 1) the pixel location on the first three axes, 2) the celestial position of the first two axes, 3) the corresponding brightness from the image and,  4) the name of the FITS file.  Fitted positions are indicated by the subcell precision of the pixel number.


Exit

   This will terminate the program.


Options Menu

 This menu contains items that control the range of values loaded into the display and the plane in the image to be loaded.  A Reload (or Open on another file) is required for a change in these options to take affect.

  Individual menu Items are:

 Set Pixel Range

 Set Plane

 Linear Display

 Nonlinear Display

Histogram Equalization

 Flip vertically

 Reload

Toolbar


Set Pixel Range

   This item brings up a dialog box which allows setting the range of pixel values.  The range of values that are present in the image plane displayed are given in the second line.  The first value entered (labeled "min.") is the minimum pixel value to be displayed and the second ("max.") is the maximum to be displayed.  Pixel values below the minimum are set to the minimum and above the maximum are set to the maximum.  0, 0 means that FITSview should determine an appropriate range for the current image; this will cause some delay in loading the image as it has to be read an additional time to determine the pixel range.  The initial values are the previously specified values.


Set Plane

   If the image contains multiple planes (frequency, polarization etc.) the desired plane number can be specified using this item.  The dialog box will initially contain the current plane number and will tell the range of values (number of planes).  Information about the number and type of planes may be obtained from the Image info item in the File menu.


Linear Display

   This option specifies a linear mapping of image pixel values to display colors.  If a Pixel Range is specified then it is used, otherwise FITSview guesses a range based on the histogram of pixel values.


Nonlinear Display

   This option specifies a nonlinear mapping of pixel values to display colors; the mapping function is the square root of the pixel value.  This option is useful for displaying an image with a large range of pixel values and uses more levels to display low brightness than the linear mapping.  If a Pixel Range is specified then it is used, otherwise FITSview guesses a range based on the histogram of pixel values.


Histogram Equalization

   This option specifies that the histogram equalization technique be applied in the display of this image.  This technique attempts to show equal numbers of image pixels in each of the colors of the display.  This is potentially useful for images with a very large dynamic range but with most of the pixel values towards one extreme of the range or the other.  If a Pixel Range is specified, the equalization process only considers pixel values in this range.  If no range is specified FITSview picks a range it thinks is appropriate.


Flip vertically

   This option causes subsequent images loaded to be flipped top-for-bottom.  The image information display notes when this option is selected. Selecting this option toggles it on and off.  Note: this option can be VERY slow for gzip compressed files.


Reload Image

   This option causes the currently selected image to be reloaded into the display using the current set of options.  This needs to be done after any of the other options in this menu have been changed in order for these changes to take effect.

   When the file is being loaded to the display, a box appears with a progress message and a cancel button.  If the message "WARNING: BAD PIXEL RANGE" appears then all of the pixels loaded are at one extreme of the range of displayed brightness.  This usually indicates inappropriate values in the Set Pixel Range in the Options menu.  This may be the result of a previous image with a very different range of pixel values.  Setting both values to zero will get the default display.


Toolbar (Windows95/NT only)

   This option toggles the toolbar on and off. The toolbar contains buttons which provide faster access to common functions to common operations than using the menu or keyboard accelerators.  Holding the cursor in a toolbar button will cause a popup box to appear giving the function of the button.  The toolbar is only available in the Windows95/NT version of FITSview.


Overview

This viewer will display and manipulate astronomical images in FITS format or FITS format images which have been compressed using the gzip

compression technique.  The file to view can be specified as a command line argument or using the Open item in the File menu.  Subsequent files can also be selected using the Open function.   Information about the displayed image can be obtained using the Image info item in the File menu.

   The header of a FITS file (or the text of a text file) may be previewed before deciding which image to load.  Once a file is displayed it can be manipulated and examined in a number of ways.  If the image is larger than the display, the scroll bars on the edge of the display will scroll around inside of the image.  Clicking the left mouse button in the display will result in the brightness and celestial position of the pixel under the cursor being displayed at the bottom of the Display control box.  A click on the right mouse button is similar except that a point model is fitted to the image near the selected pixel; the results are given in the Display control box.  These brightness and position displays can be logged to a text file by selecting the "Log positions" option in the file menu.

   Standard World Coordinate System (WCS) coordinates are supported as well as the astrometric plate parameters from the Digitized Sky Survey (DSS) and the IRAF CD matrix. Positions can be displayed in either equinox B1950 or J2000 if the equinox given in the image is either of these.

   The brightness and contrast of the image can be adjusted using the horizonal scroll bars  at the top of the Display control box.  Moving the slider to the right will increase the contrast or the brightness.  If the range of pixel brightness  of the portion of the image of interest is significantly smaller than the total range, contrast and brightness adjustments may be insufficient.  In this case, a limited range of pixel values can be displayed using the Pixel Range dialog box in the Options menu,  Alternately, the nonlinear option in the Options menu may display the desired range of brightness.  Blanked pixels always appear as black.

   The image can be displayed in color using one of two color schemes, Color Contour and Pseudo Flame in the Colorize menu.  Color Contour is an 8 color scheme  which gives a contouring effect and Pseudo Flame is a continous color pseudo coloring scheme. giving the image a flame like quality.  Option Grayscale is a black and white coloring scheme.  The order of the color table (black becomes white etc.) is reversed using the Reverse item.   Brightness and contract controls also work on colorized images.  The color, contrast and brightness can be reset using the Reset item on the Colorize menu,

   When an image is initially loaded, generally the first plane in the file is displayed.  If the image contains multiple frequency or polarization planes,  other planes can be loaded using the Set Plane dialog box in the Options window.  The number and type of planes in the file can be determined using the Image Info item in the File menu.  A cube can be displayed as a movie (using the "Movie" item in the Movie menu) to show a range of planes in sequence or by selecting planes at random.

   An image can be zoomed in or out using the Zoom menu and selecting the desired magnification factor.  Zooming in (factor > 100%) is done by replicating pixels and zooming out (magnification <100%)  by displaying only a subset of the pixels.  Zooming is centered on the current scroll position controlled by the image scroll bars.  Selecting a zoom factor of 100% undoes the effects of zooming.

   Celestial positions determined from mouse clicks can be refined using the Fit Point Model option in the Position menu.  This will fit an accurate position and flux assuming a point object near the position of the last mouse click.  The results will be displayed in the lower left corner.  Clicking the right mouse button will  have the same result. The Mark Position item in the Position menu will bring up a dialog box in which the celestial coordinates of an object of interest can be entered; alternately a list of positions can be given in a file.  The corresponding location(s) on the image will be marked.

   Two images can be compared using the Blink facility controlled by the Blink menu.  Blinking will alternately display one image and then the other.  The first image is loaded into the display and desired adjustments are made.  It is then copied into the Blink image using the Copy to blink store item in the Blink menu.  The second image is then loaded into the display and adjusted as desired.  The Blink images item on the Blink menu will then begin blinking.  The dwell time on each image can be controlled using the scroll bar in the blink dialog box.  The Quit button on the dialog box ends blinking.   If the two images have pixels coincident on the sky, the zoom and scroll used are that for the current display (the one visible before the blink starts).  If the pixels are not aligned, blinking uses the scroll, zoom and display setup for the first image that were in effect when it was copied to the Blink image and the current setup for the second (normal display) image before the blink began.  The Swap current and blink item swaps the current and blink images.

   Once an image is loaded, its display can be written to a device independent bitmap (.BMP) format file.  This file will have the color, brightness and contrast of the current display but is unaffected by zoom and scroll.  This file may then be read into other programs.  The currently displayed portion of an image can be printed using the Print item in the File menu.


 File Menu

This menu includes a number items related to files.  Files to be viewed using the Open function or previewed using the Preview function may be either regular FITS (or text) files or these files after compression by the gzip method.  These compressed files are usually indicated by a ".gz" at the end of the file name although this is not necessary.

Open

   This item will bring up a file browser dialog box to select the FITS file to load.  When a file is loaded, the previous image is discarded.  The title bar of the main window gives the name of the currently loaded file.

   Note: the default extension of the FITS file is *.FIT; if the files have other names then the file mask needs to be set to *.* in the file dialog box.

   If the file is not a FITS image then error messages will be displayed in dialog boxes.  Click the OK button to continue and select a valid FITS image file.

   When the file is being loaded to the display, a box appears with a progress message and a cancel button.  If the message "WARNING: BAD PIXEL RANGE" appears then all of the pixels loaded are at one extreme of the range of displayed brightness.  This usually indicates inappropriate values in the Set Pixel Range option in the Options menu.  This may be the result of a previous image with a very different range of pixel values.  Setting both values to zero will get the default display.  If the FITS header does not contain the maximum and minimun values then these may have to be set using the Set Pixel Range item.

Preview

   This item will display up to about 1000 lines of the header of a selected FITS file or text file in a scroll box.  This allows deciding which image to load or reading explanatory text.  The first line of the header of a FITS header is:

SIMPLE  =                     T     /possibly some comment

An FITS image file has a line near the beginning of the form:

NAXIS1   =              nnn        /possibly some comment

where nnn is an integer larger than 0.  The size of the image is given by the NAXIS1 and NAXIS2 entries.  Information about the image may be contained in HISTORY or COMMENT lines.

Save as

   This item will cause the currently displayed image to be written to a FITS file.  A file selection dialog box will pop up in which the desired name of the new file is to be entered.  The output file is in uncompressed form whether or not the input image is.

Image info

   This item will display information about the current image including positions, frequencies, observation dates, etc.  The dismiss button clears this display.

Print

   This item will print the currently displayed image.  The current brightness, contrast and color are used although the color table is reversed as this usually gives much better results.  The region of the image printed is that in the current display; a combination of zoom, scroll and resizing the window allows selecting an arbitrary region of the image.  The printed version gives information about the image and the location of the center and the size of the displayed region.

Save BMP

   This item will cause the currently displayed image to be written to a device independent bitmap (BMP) format file.  A dialog box will allow selection of the directory and file name to be written.  The output file will have the color, contrast and brightness of the current display but is unaffected by scroll and zoom.

Log positions

   This will toggle the logging of brightnesses and positions selected by a mouse button click or fitting a point model to the image.  When this is turned on, a dialog box will allow selection of the text file.  The logging file contains one line per position containing 1) the pixel location on the first three axes, 2) the celestial position of the first two axes, 3) the corresponding brightness from the image and,  4) the name of the FITS file.  Fitted positions are indicated by the subcell precision of the pixel number.

Exit

   This will terminate the program.


Options menu

This menu contains items that control the range of values loaded into the display and the plane in the image loaded.  A Reload (or Open on another file) is required for a change in these options to take affect.

Set Pixel Range

   This item brings up a dialog box which allows setting the range of pixel values.  The range of values that are present in the image plane displayed are given in the second line.  The first value entered (labeled "min.") is the minimum pixel value to be displayed and the second ("max.") is the maximum to be displayed.  Pixel values below the minimum are set to the minimum and above the maximum are set to the maximum.  0, 0 means use the full range in the image.  The initial values are those used to load the current display.

   If the FITS file does not contain the actual maximum and minimum values the defaults may be a very poor guess.  In this case load the image and use the Set Pixel Range option to set the range of values to be loaded to the range displayed in the Pixel range box.

Set Plane

   If the image contains multiple planes (frequency, polarization etc.) the desired plane number can be specified using this item.  The dialog box will initially contain the current plane number and will tell the range of values (number of planes).  Information about the number and type of planes may be obtained from the Image info item in the File menu.

Linear display

   This option specifies a linear mapping of image pixel values to display colors.

Nonlinear display

   This option specifies a nonlinear mapping of pixel values to display colors; the mapping function is the square root of the pixel value.  This option is useful for displaying an image with a large range of pixel values and uses more levels to display low brightness than the linear mapping.

Flip vertically

   This option causes subsequent images loaded to be flipped top-for-bottom.  The image information display notes when this option is selected. Selecting this option toggles it on and off.  Note: this option can be VERY slow for gzip compressed files.

Reload

   This option causes the currently selected image to be reloaded into the display using the current set of options.  This needs to be done after any of the other options in this menu have been changed in order for these changes to take effect.

   When the file is being loaded to the display, a box appears with a progress message and a cancel button.  If the message "WARNING: BAD PIXEL RANGE" appears then all of the pixels loaded are at one extreme of the range of displayed brightness.  This usually indicates inappropriate values in the Set Pixel Range in the Options menu.  This may be the result of a previous image with a very different range of pixel values.  Setting both values to zero will get the default display.


Zoom menu

This menu controls zooming of the image.

25%

   This will reduce the size of the displayed image to 1/4 of its normal size by discarding 3 out of 4 rows and columns.

50%

   This will reduce the size of the displayed image to 1/2 of its normal size by discarding alternate rows and columns.

100%

   Resets the zoom to its initial setting.

200%


 Position Menu

This menu contains functions related to celestial positions .

Set Equinox

   This option allows specifying the equinox (B1950 or J2000) of the celestial

coordinates displayed or entered.  Thus, if the image is in J2000 coordinates and

you have a position in B1950, clicking on the B1950 button in the Set Equinox dialog

box will cause positions displayed after a mouse click in the image to be equinox

B1950.  Furthermore, the position specified to Mark Position will be B1950.  See the

'Image Info'  box in the File menu to determine the equinox of the image.

   The dialog box invoked by this menu item has three options: 1) use the equinox of

the image (default), 2) equinox J2000 and 3) equinox B1950.  Note, if the image does

not specify the equinox then this selection has no effect.

Fit Point Model

   Fit a point model near the position of the last pixel selected by the cursor using the left mouse button.  The result of the fit is shown in display control box.  If the values given are the result of a fit, the bottom line of the display will read "fitted".  If for some reason the fit fails the bottom line will read "fit failed!".  This function can be simplified by clicking the right mouse button which will also cause a fit to be attempted at the selected position.

Mark Position

   This option lets you mark a particular celestial position in the current image. Selecting this option brings up a dialog box into which the desired celestial position is entered; optionally, the name of a text file can be given with a list of positions.  The selected positions are marked in the displayed image by a cross whose inner positions are not shown so as not to obscure the image.  The cross is marked in the display by replacing the previous values with that of the brightest pixel in the image.  These markers will persist until the display is reloaded with the same or another image and will appear if the image is printed.  Note that the cross may not be visible on some reduced zoom displays as the marked pixels may not be among those shown.

When the desired values are entered into this dialog box, the "OK" button will proceed to mark the image and set the scroll to center the last position marked.  The "cancel" button dismisses the box without marking any positions and the "Help" button asks for this explanation.

   The size of the cross can be controlled by the two values in the line labeled "size".  The first of these is the "inner" size of the cross or the distance from the center in pixels in which the cross is not marked.  The second value is the "outer" size or the distance in pixels from the center over which the cross appears.

   If multiple positions are to be marked they can be entered in a text file prepared by a text editor (e.g. EDIT).   Each line of this file should have an entry of the form:

RA:h RA:m RAs  Dec:d Dec:m Dec:s inner outer

where RA:h, RA:m, RA:s are the hours, minutes and seconds of the Right Ascension and Dec:d, Dec:m, and Dec:s are the degrees (with -sign if in the south), minutes, and seconds of the Declination.  Inner and outer are the inner and outer sizes of the marking cross in pixels.  An example is:

  12 34 23.7898  -15 23 45.634 3 10

   To select a file containing positions, hit the "file" button for a directory browser to specify the text file.  If there are positions in the file that are out of the image then the number of these positions are reported and the remainder marked.

Lookup Position

   If the current FITS file directory contains a special index, this item allows specifying

a celestial position and FITSview will determine which image (if any) contains that

position, load the image, and center the display on that position.  The equinox of the

position can be specified using the 'Set Equinox' option in this menu.  Once the

desired position is entered in the dialog, the 'Lookup' button will cause FITSview to

attempt to find and load the desired image.  The cancel button dismisses the dialog

with no change to the current image.

   The index file in the FITS file directory should have name 'findex.txt' and obey the

following guidelines.

line 1:

   This line must specify the equinox of the image field centers e.g.

equinox 1950.0

Only B1950 (1950.0) and J2000 (2000.0) are supported.

lines 2...:

   These lines give the name of the file, the central position, the half width (degrees) in

RA and Declination and a priority number.  The file containing the specified position

with the highest priority number is the one selected.  Comments may be given by

putting an '!' in the first column.  The entry is free format (an entry must be confined to

a single line) and the structure of a file entry is:

filename hh mm ss.s dd mm ss.s hw.ra hw.dec priority

Examples follow:

! These images are from the long lost Summarian clay tablets

! name       RA            Dec     Delta_RA   Delta_dec priority

sky.fit      11 23 56.234 82 17 56.7 1.87       .25        1

south.fit.gz 17 23 54.1  74 4 53     3.65        1         2

   Note: the half width in RA is half the number of cells in RA times the cell spacing divided by the cosine of the declination to account for the converging lines of RA towards the poles.


Blink menu

This menu controls blinking.

Copy to blink store

   Copies the current image and its current display state to the Blink image.  The currently displayed image will then disappear.

Blink images

   This will bring up a dialog control box and start blinking the images.  The dwell time is controlled using a scroll bar and the Quit button terminates  blinking.  The title bar of the main window gives the name of the currently displayed file.  When blinking stops, the current image is displayed.  If the images have aligned pixels on the sky (the only case that makes sense) then the zoom and scroll of the blink image is forced to that of the current.  Otherwise, the zoom and scroll are those set for each of the images and there may be no correspondence between the pixels of the two images.

Swap current and blink

   This will swap the current and blink images.  This allows changing the color table of the blink image or examining values or positions in the image.


 Movie menu

Movie

   This will bring up a dialog box which controls displaying planes in a movie-like fashion where the display is periodically updated with the next plane.  Planes can be shown as movies or selected manually using the scroll bar.  The current plane is indicated by the location of the slider in the scroll bar and the text lines under it giving the plane number and the value along this axis in the cube.  The values of zoom, scroll, pixel range, and color map in effect when the Movie item is selected will be used for all displays.

   The movie function is controlled by the values in the text boxes labeled "planes" (the start plane for the movie), "to" (the final plane for the movie), and "Dwell (sec)" (the dwell time on each frame in seconds).  These values may be modified by clicking on the box and typeing in new values. The movie is started using the "Play" button and can be stopped prematurely by the "Stop" button.  The movie proceeds through the selected range once.  NB: the speed of the movie may be slower than indicated by the "Dwell" value if it takes longer than this to load the next plane from the disk.

   The displayed plane can be controlled manually using the scroll bar.  The selected plane will remain displayed until another plane is selected.

   The "Quit" button exits movie mode and resumes the normal display.  The "Help" button requests this information.


 Colorize menu

This menu controls the colorizing of the image which is intrinsically monochromatic.  The brightness and contrast controls will modify the color schemes.

Color Contour

   This scheme uses a small number of colors to represent the image.  This gives a color contour effect.

Pseudo Flame

   This scheme uses a continous set of colors and intensities to represent the image with a pseudo coloring scheme giving the image a flame like quality.

Grayscale

   This function uses shades of gray to represent the image.

Reverse colors

   This function reverses the order of the color table causing black to become white etc.

Reset colors

   This resets the colors to shades of gray and resets the brightness and contrast controls.


 Help menu

This menu controls informative displays about the program.

Help

   Invokes the windows Help facility to display this information about the program.

About

The usual copyright notice as well as indications of the available memory and system resources.


 Display control

The display control box contains scroll bars to control the brightness and contrast of the displayed image and information about pixels selected in the image.  Initially, this box is at the left hand side of the image display and occupies a section of the display which is not used for displaying the current image. This box may be moved, allowing the entire area in the FITSview window to be used for displaying an image.  Resizing the FITSview window will cause the display control box to return to its initial configuration.


 Image position

   The celestial position and brightness of a given pixel can be determined by clicking the left mouse button when the cursor is on the desired position in the image display.  The results are shown at the bottom of the Display control.  A more accurate position may be obtained for small objects using the Fit Point Model item in the Position menu or by using the right mouse button to select the pixel. The initial position for the fitting must be within one pixel of the local maximum (or minimum) being fitted.


 Image scrolling      If the displayed image is larger than the display area there will be scroll bars on the display area.  These scroll bars can be used to move the visible area around on the image.


 Image enhancement

   The horizional scroll bars in the Display control box set the brightness and contrast of the image.  Moving the slider towards the right will increase brightness or contrast.  The scroll bars are labeled "Brightness" and "Contrast" and the value in parentheses are relative values between 0 and 255.


Zoom
Zoom menu

This menu controls zooming of the image.

Individual menu Items are:

 25%

 50%

 100%

 200%

 400%

 800%

 1600%


25%

   This will reduce the size of the displayed image to 1/4 of its normal size by discarding 3 out of 4 rows and columns.


50%

   This will reduce the size of the displayed image to 1/2 of its normal size by discarding alternate rows and columns.


100%

   Resets the zoom to its initial setting.


200%

   Each column and row of the image is repeated to make the image appear twice its natural size,


400%

   The image is made to appear 4 times normal size


800%

   The image is made to appear eight times normal size.


1600%

   The image is made to appear sixteen times normal size.


Position Menu

This menu contains functions related to celestial positions .

Individual menu items:

 SetEquinox

 Fit Point Model

 Mark_Position

 Lookup Position


Set Equinox

This option allows specifying the equinox (B1950 or J2000) of the celestial coordinates displayed or entered.  Thus, if the image is in J2000 coordinates and you have a position in B1950, clicking on the B1950 button in the Set Equinox dialog box will cause positions displayed after a mouse click in the image to be equinox B1950.  Furthermore, the position specified to Mark Position will be B1950.  See the 'Image Info'  box in the File menu to determine the equinox of the image.   The dialog box invoked by this menu item has three options: 1) use the equinox of the image (default), 2) equinox J2000 and 3) equinox B1950.  Note, if the image does not specify the equinox then this selection has no effect.


Fit Point Model

  Fit a point model near the position of the last pixel selected by the cursor using the left mouse button.  The result of the fit is shown in display control box.  If the values given are the result of a fit, the bottom line of the display will read "fitted".  If for some reason the fit fails the bottom line will read "fit failed!".  This function can be simplified by clicking the right mouse button which will also cause a fit to be attempted at the selected position.


Mark Position

  This option lets you mark a particular celestial position in the current image. Selecting this option brings up a dialog box into which the desired celestial position is entered; optionally, the name of a text file can be given with a list of positions.  The selected positions are marked in the displayed image by a cross whose inner positions are not shown so as not to obscure the image.  The cross is marked in the display by replacing the previous values with that of the brightest pixel in the image.  These markers will persist until the display is reloaded with the same or another image and will appear if the image is printed.  Note that the cross may not be visible on some reduced zoom displays as the marked pixels may not be among those shown.

When the desired values are entered into this dialog box, the "OK" button will proceed to mark the image and set the scroll to center the last position marked.  The "cancel" button dismisses the box without marking any positions and the "Help" button asks for this explanation.

   The size of the cross can be controlled by the two values in the line labeled "size".  The first of these is the "inner" size of the cross or the distance from the center in pixels in which the cross is not marked.  The second value is the "outer" size or the distance in pixels from the center over which the cross appears.

   If multiple positions are to be marked they can be entered in a text file prepared by a text editor (e.g. EDIT).   Each line of this file should have an entry of the form:

RA:h RA:m RAs  Dec:d Dec:m Dec:s inner outer

where RA:h, RA:m, RA:s are the hours, minutes and seconds of the Right Ascension and Dec:d, Dec:m, and Dec:s are the degrees (with -sign if in the south), minutes, and seconds of the Declination.  Inner and outer are the inner and outer sizes of the marking cross in pixels.  An example is:

  12 34 23.7898  -15 23 45.634 3 10

   To select a file containing positions, hit the "file" button for a directory browser to specify the text file.  If there are positions in the file that are out of the image then the number of these positions are reported and the remainder marked.


Lookup Position

   If the current FITS file directory contains a special index, this item allows specifying a celestial position and FITSview will determine which image (if any) contains that position, load the image, and center the display on that position.  The equinox of the position can be specified using the 'Set Equinox' option in this menu.  Once the desired position is entered in the dialog, the 'Lookup' button will cause FITSview to attempt to find and load the desired image.  The cancel button dismisses the dialog with no change to the current image.  The index file in the FITS file directory should have name 'findex.txt' and obey the following guidelines.

line 1:

   This line must specify the equinox of the image field centers e.g. equinox 1950.0

Only B1950 (1950.0) and J2000 (2000.0) are supported.

lines 2...:

   These lines give the name of the file, the central position, the half width (degrees) in RA and Declination and a priority number.  The file containing the specified position with the highest priority number is the one selected.  Comments may be given by putting an '!' in the first column.  The entry is free format (an entry must be confined to a single line) and the structure of a file entry is:filename hh mm ss.s dd mm ss.s hw.ra hw.dec priority

Examples follow:

! These images are from the long lost Summarian clay tablets

! name       RA            Dec     Delta_RA   Delta_dec priority

sky.fit      11 23 56.234 82 17 56.7 1.87       .25        1

south.fit.gz 17 23 54.1  74 4 53     3.65        1         2

   Note: the half width in RA is half the number of cells in RA times the cell spacing divided by the cosine of the declination to account for the converging lines of RA towards the poles.


Movie
 Movie Menu

Movie

   This will bring up a dialog box which controls displaying planes in a movie-like fashion where the display is periodically updated with the next plane.  Planes can be shown as movies or selected manually using the scroll bar.  The current plane is indicated by the location of the slider in the scroll bar and the text lines under it giving the plane number and the value along this axis in the cube.  The values of zoom, scroll, pixel range, and color map in effect when the Movie item is selected will be used for all displays.

   The movie function is controlled by the values in the text boxes labeled "planes" (the start plane for the movie), "to" (the final plane for the movie), and "Dwell (sec)" (the dwell time on each frame in seconds).  These values may be modified by clicking on the box and typing in new values. The movie is started using the "Play" button and can be stopped prematurely by the "Stop" button.  The movie proceeds through the selected range once.  NB: the speed of the movie may be slower than indicated by the "Dwell" value if it takes longer than this to load the next plane from the disk.

   The displayed plane can be controlled manually using the scroll bar.  The selected plane will remain displayed until another plane is selected.

   The "Quit" button exits movie mode and resumes the normal display.  The "Help" button requests this information.


Color
 Colorize menu

This menu controls the colorizing of the image which is intrinsically monochromatic.  The brightness and contrast controls will modify the color schemes by modifying the color table

Color Contour

   This scheme uses a small number of colors to represent the image.  This gives a color contour effect.

Pseudo Flame

   This scheme uses a continous set of colors and intensities to represent the image with a pseudo coloring scheme giving the image a flame like quality.

Grayscale

   This function uses shades of gray to represent the image.

Reverse colors

   This function reverses the order of the color table causing black to become white etc.

Reset colors

   This resets the colors to shades of gray and resets the brightness and contrast controls.


Help
 Help menu

This menu controls informative displays about the program.

Help

   Invokes the windows Help facility to display this information about the program.

About

The usual copyright notice as well as indications of the available memory and system resources.


 Display control

The display control box contains scroll bars to control the brightness and contrast of the displayed image and information about pixels selected in the image.  Initially, this box is at the left hand side of the image display and occupies a section of the display which is not used for displaying the current image. This box may be moved, allowing the entire area in the FITSview window to be used for displaying an image.  Resizing the FITSview window will cause the display control box to return to its initial configuration.


 Image position

   The celestial position and brightness of a given pixel can be determined by clicking the left mouse button when the cursor is on the desired position in the image display.  The results are shown at the bottom of the Display control.  A more accurate position may be obtained for small objects using the Fit Point Model item in the Position menu or by using the right mouse button to select the pixel. The initial position for the fitting must be within one pixel of the local maximum (or minimum) being fitted.


Image scrolling

If the displayed image is larger than the display area there will be scroll bars on the display area.  These scroll bars can be used to move the visible area around on the image.


 Image enhancement

   The horizional scroll bars in the Display control box set the brightness and contrast of the image.  Moving the slider towards the right will increase brightness or contrast.  The scroll bars are labeled "Brightness" and "Contrast" and the value in parentheses are relative values between 0 and 255.