Image file (window)¶
This preview window is used to display the content of an external image file.
Activating the dialog¶
The dialog can be activated:
from the main menu:
.
When a file is opened, the program checks its content and decides which kind of preview window will be activated. Each file is presented in a separate window.
Dialog controls¶

Preview window for CCD image files¶
(1) The CCD image is displayed in the preview area. It is possible to switch between positive and negative style in the “Preferences” dialog.
(2) When you place a cursor over an image, the coordinates and the pixel value is displayed in the status bar.
(3) You can zoom the preview in and out by means of the zoom icons on the toolbar. The actual magnification is shown here.
(4) The local menu bar provides following functions:
Menu File:
Open - open another file, this is an equivalent to selection
from the main window.Save as - save the image to a file in FITS format. To export the image in one of common raster image formats, use the ‘Export’.
Export - export the image to a file in one of common raster image formats, currently the PNG and JPEG formats are supported. It is possible to adjust the size of the resulting image.
Show properties - display the further details about the file. Full header preview is available in separate window.
Close - close this window
Menu View:
Rulers - turn on/off the rules that are shown on the top and left side of the preview area
Pseudo-color image - switch between rendering of pixel intensities in pseudo-color scale and a gray scale.
Menu Image:
Horizontal flip - flip image from left to right
Vertical flip - flip image from top to bottom
Menu Tools:
Gray scale - show a gray scale or a pseudo-color scale on the right side of the dialog.
Quick photometry - show the Quick photometry tool - explained below.
Profile - show the Profile tool - explained below.
Histogram - show the histogram and statistics.
Quick Photometry tool¶
The Quick Photometry tool is a tool which computes basic photometric properties of an object on a frame. The main goal of this tool is to provide an estimation of the FWHM value (the important input parameter of the photometry process).
Because this tool does simplified version of aperture photometry, the results are informative only and shouldn’t be used elsewhere. Also, it doesn’t require a proper calibration to be performed first.
To activate the tool, select
from the local menu. A new panel on the right side of the preview window appears.
Quick photometry tool¶
Using the left mouse button, click on the image (1), close to an object. The program automatically finds the nearest local maximum, so you don’t need to be accurate. The computation stars automatically and the results are displayed the the right panel (2).
The following object parameters are presented:
Center - coordinates of the local maximum.
Max - pixel value in local maximum
Background - mean background level, computed as a robust mean of pixels in the sky annulus.
Noise - background noise level, computed as a standard deviation of pixels in the sky annulus.
FWHM - object’s width, computed full width at half maximum.
Aperture - aperture radius used for computing the object’s signal.
Signal - object’s signal, sum of pixels in the aperture, mean background level is subtracted.
S/N ratio - signal to background noise ratio, displayed in decibels: SNR = 10.log(S/N).
(3) Several dimensions are presented in the image area.
Two blue circles show the annulus which is used to estimate the background properties.
A red circle shows the object’s average FWHM.
A green circle shows the size of the aperture.
It is also possible to change some parameters:
(4) Aperture radius in pixels
(5) Inner radius of the sky annulus in pixels
(6) Outer radius of the sky annulus in pixels
Profile tool¶
The Profile tool is used to check the shape of objects. It shows a curve of pixels values along a line.
To activate the tool, select
from the local menu. A new panel on the bottom of the preview window appears.
Profile tool¶
Using the left mouse button, draw a line on the image (1), crossing the center of an object. The profile is drawn in the graph (2). You can adjust the graph style (3). The following parameters are displayed in the information box (4):
Min - minimum pixel value.
Max - maximum pixel value
Mean - mean pixel value of pixels in the profile.
St. dev. - standard deviation of pixels in the profile.
Histogram tool¶
The Histogram tool shows a histogram of pixel values and some related statistics.
To activate the tool, select
from the local menu. A new panel on the bottom of the preview window appears.
Histogram tool¶
The histogram is shown in the left part (1) of the tool. The following parameters are displayed in the text area on its right side (2):
Min - minimum pixel value
Max - maximum pixel value
Mean - mean pixel value of all pixels
St. dev. - standard deviation of all pixels
See also