Open this dialog using the from the Process > Calibration Menu or the 
button on the Animation Pane.
Combine Image Set
The Combine Image Set command combines the members of a displayed Image Set into a single new image. Several statistical methods are available for combining the images and for adjusting ("normalizing") them to a common reference value (see Image Combining Methods).Normalization is used to adjust the images to a common statistical value when using any combining method that rejects bad data such as the mean, rank, and alpha methods. Statistical methods for computing the normalization values are discussed in Image Region Statistics. This command is often used following image registration. The related Combine Files command works with images in files, rather than displayed in memory.
Open this dialog using the from the Process > Calibration Menu or the button on the Animation Pane.
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Properties of the Combine Image Set Command |
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Profile |
Selects the parameter profile for this command. |
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Method |
This list box selects the type of processing used to combine the image values. These are described in Image Combining Methods. If the combining method takes Properties, these are presented in 1 or 2 fields to the right of the Method selection box. Some methods have no Properties, so no fields are visible. For example, in the picture above, the Mean - Sigma Clipped method uses 2 Properties: the upper number of sigmas to clip ("High sigma") and the lower number of sigmas to clip ("Low sigma"). |
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Image Normalization |
This control group specifies whether the images are adjusted (normalized) to a common statistical value before being combined. If normalization is not set to "none", then the[Normalization Statistic] button opens the Region Statistics dialog. In this dialog you specify how the normalization is to be computed, including the target statistic and the region over which it is calculated. See the discussion below. |
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[Normalization Statistic] |
Click this button to open the Region Statistics dialog for selecting normalization properties. |
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Pixel Type |
Select a Pixel Type for the output image that can accommodate the increased signal and dynamic range of the combined images. For example, if combining a large number of 16-bit integer type images it is usually prudent to set the Pixel Type of the output image to 32 bit real. |
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Check this box to update the exposure time in the output image so that it is characteristic of the exposure time of an equivalent single image. This can be used to maintain the image flux, or the value of signal per unit time. This option also updates the mid-time of the exposure based on the weighted combination of the mid-times of all the combined images. The mid-time is saved in the keywords DATE-MID and TIME-MID, which can be used by the photometry tools. |
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Check this box to normalize the combined image to a reference value of 1.0. The Normalization settings are used to compute and apply the scaling. Use this setting when using the command to create a flat field correction frame (see the Apply Flat Field method). |
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Check this box to list detailed messages about the combining process. |
Normalization is used to adjust the images to a common statistical value when using any combining method that rejects bad data. This is essential when using a combining method that performs rejection of bad data, such as the Sigma Clipping, Min/Max or Median methods.
Choose the normalization operation, Scale, Offset, or None, according to the nature of the difference between the images being combined.
If the pixel values differ because of an additive offset, like variations in the CCD bias offset, select Offset.
If the images differ because of a scale factor, as caused by differences in illumination or exposure time, select Scale.
The None setting disables normalization.
This part of the combining procedure works like to the Normalize Image command.
Math Commands, Combine Files, Normalize Image, Image Set, Image Combining Methods, Image Region Statistics, Region Statistics, Register Images, Profiles
Adjust Exposure time