PictorView XT allows you to view and process numerous types of images, including
BMP, FITS, PCX, TIFF, and GIF. The software can read most images in these
formats, and convert between them using the File, Save As command.
|IMPORTANT NOTICE! Never use a telescope or spotting scope to look at the Sun! Observing the Sun, even for the shortest fraction of a second, will cause irreversible damage to your eye as well as physical damage to the telescope or spotting scope itself. |
There are also numerous image processing functions available for any openimage file. All image processing functions can be accessed by selecting
Image from the top level menu. These functions can be divided into the areas
of calibration / cleanup and transformations.
Note that all image processing commands can be reversed by selecting Edit,
Calibration and cleanup functions:
Cleanup functions are generally performed on an image taken from the Pictor
XT camera. Their purpose is to provide a better picture of the object being
imaged. Most of the functions involve calibration frames. The cleanup functions
available are: Subtract Bias Frame, Subtract Dark Frame, and Divide Flat
Field. Each of these functions will prompt for a file name,
shown in the window.
After selecting the file, the operation selected will be performed, and
the transformed image will automatically be displayed. Note that the calibration
file does not have to the same type as the source file. For more information
on the types of calibrations available and their purpose, see the CCD Tutorial.
Note that you should not subtract a bias frame and a dark frame since the
dark frame has the bias frame information in it as well. See the section
on taking images, and the Imaging Tips section for more information.
Editing background and range can also bring out hidden image detail. This
can be done through the menu pick or by pressing the arrow keys.
Scaling and Histogram functions:
These are the most powerful of the image processing functions available
within PictorView XT, including scaling, histogram equalization, posterization,
and brightness and contrast. This
windowis accessed through the Image Scaling Tool on the toolbar or the Image Scaling
option under the Image Menu.
The green area graph shows the distribution of pixels; the histogram; of
the image. The X axis is the color, from black to white, and the y axis
shows the number of pixel of that particular shade of grey are in the image.
The green line shows the scaling of the image; what you see on the screen.
Linear is the default, and other options are logarithmic, dynamic, and exponential.
Moving the red cursors will chop off parts of the image data; for example
if all the histogram data was together like the example, but there were
some sharp peaks off to the side, these would probably be anomalous data,
and could be chopped off by moving the red cursor past them. The brightness
function will uniformly increase the brightness of the image, and contrast
will increase or decrease the dynamic range of the image.
The Image Information dialog is discussed in more detail in the Imaging
Tips section; it is mentioned here because it is always a good idea to record
basic information about the image being processed. PictorView XT supports
the standard FITS information, and also lets the user save this information
when working with other file formats as well. (This is done by placing the
information in a .txt file with the same name as the image file). This function
is accessed from the Image Menu or the clipboard icon on the toolbar.
The fields for height, width, bits per pixel, scale factor, zero offset,
date and time, exposure, and camera temperature are automatically filled
out when the image is created using PictorView XT. Location, Observer, Telescope
and Equipment are also filled out automatically if you entered this information
in the Set User Preferences window. (for imported images this information
may not be available).
The merge images function allows the user to merge two images into one in
a variety of different ways. This function is available under the Image
The image file to combine is the file to be added to the current file. Note
that the image file to be added does not have to be the same file type as
the current image (i.e. you can add a GIF to a BMP). The types of combinations
available will produce different results. The type you will probably use
most is Median Combine or Average; as this will prevent the image from becoming
too bright as it could with a straight Add combination. The x and y offset
is the distance to move the new image from the 0,0 point of the old one.
For most images, this will be 0,0, unless the new image is offset from the
old one. If this is the case, open the new image file normally, then look
at the two images side by side. Look for a point that is known on both images.
Get the coordinates for the point on both images (remember the coordinates
are shown on the bottom status bar). Subtract the old coordinates from the
new coordinates and enter the results in the x and y offset fields here.
The scaling factors are the amount of weight to give one image over the
other one; usually this will be 1 to 1.
This is not really processing, but more of a discovery tool. The idea is
to take an exposure of an area or an object, then compare it to an earlier
exposure by blinking them rapidly. Since the exposures may not be identical,
an offset may be needed. During the blinking, any differences between the
objects will stand out, thereby providing the chance to discover such things
as comets, asteroids, and supernovae. This function is accessed from the
Image Menu or the blinking icon on the toolbar. The X and Y offsets allow
you to adjust the blink image to align perfectly with the current image.
This can be done while blinking, and will make any differences between the
two images stand out.