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Meade Pictor XT-Series CCD Autoguider/Imagers
 Section 13: Viewing and Processing Images
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.
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.

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, then Undo.

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, as 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.

Image Information:

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).

Merge Images:

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 Menu.

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.

Blinking Images:

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.

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