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Here, the processing procedure of the ART's 'first light' images will be outlined. It is by no means the best or only way to process images. It was used because it quickly produced nice results.
Firstly, all the raw images of a given object should be opened in MaxIm. If the observer has completed the procedure to get 'Master' frames in the previous lesson then the calibration process should be simply to use the ''Calibrate All'' command. MaxIm is advanced enough to know what binning has been used, the exposure time and filter in each image and therefore selects the various calibration frames to be applied to each image. It can even calibrate windowed images with the same window from a corresponding calibration frame automatically.
The observer should allow this process to complete and then he should check each image individually to make sure that the calibration has not gone wrong. The images should be clear and there should be no large shadows or artefacts if the raw data was good.
Once the observer has checked that the calibrated frames are good he should save them with filenames indicating that they are calibrated and which raw image from which they were made. Close all the images when they are renamed.
Once all the images are closed the stacking process can begin. In MaxIm, click ''Process'' and then ''Stack...'' A window should appear. Click the ''Add Files...'' button and select each file that needs to be stacked and then click ''Open''. The files should appear listed on the left of the window, classified according to their filter. Check that these assigned filters are the filters expected. The images need not be auto-calibrated since they have been calibrated manually already.
Next go to the ''Align'' tab. This is where the images get aligned before stacking. Right click on the topmost file listed on the left and select 'Reference Frame'. The method used to align the 'first light' images was the ''Manual 2 stars'' method. The ''Auto - star matching'' method should be quick and totally automated but perhaps observers would prefer not to use the computer's method.
To align images with the ''Manual 2 stars'' method select the reference frame. Choose a bright, easy to find star on the frame (not too near the edge) and label it as '1' using the blue circular cursor. The computer should calculate the centroid of the star labelled so one does not need to be too precise about labelling the very centre of the star. The scroll wheel can be used to zoom in and out to make the aligning easier. Next, select the next image in the series of images. Locate the same star as before and label it '1' as well. Repeat this process for all the images of a given object. Now return to the reference image. Find another obvious star, preferably on the far side of the frame from the star labelled '1'. Label this star '2' (''Auto next'' should have changed the cursor if the previous steps were completed properly) and continue until all the images have the same stars in them labelled '1' and '2'. The result of the alignment can be previewed. The images will be inlaid over each other in different colours. The colours should overlap very closely if the alignment was done well.
Now go to the ''Colour'' tab. The ratios of the output colour to input colour can be changed here. This allows faint details brightest in a particular filter to be highlighted. All the ART images were combined in the default 1:1:1 ratio. The 'weight' of the luminance frame can be changed too. If the luminance frame is considerably brighter than the colour frames then it would dominate the final image. To prevent this decrease the weight of the luminance image (if there is one). The stacking process can be redone as many times as is required to get the perfect image.
Regarding the default 1:1:1 ratio it may be desirable to alter this. The CCD is less sensitive to Blue and Red light than Green light which can give combined images very green or yellow appearances. Therefore imagers may want to experiment with boosting the red and blue in their images to compensate. the sensitivity of the main imaging camera can be found at the bottom of this [[http://www.starlight-xpress.co.uk/SXVF-H35-36.htm | page]].
Finally, go to the ''Combine'' tab. It has been suggested that the best method for combining 6 or fewer images is the 'Median' method which was how most of the ART images were combined. For more than 6 images the 'Sigma Clip' method has been recommended. Select the recommended method from its drop sown menu and then click ''Go''. This process may take some time. The combined image will now be displayed on screen.
The levels and curves of the three separate colour channels can still be manipulated even though they are combined. The buttons which display the ''levels'' and ''curves'' windows are located at the right of the toolbar at the top of the screen. The effects of manipulating the levels and curves can be previewed by hitting the ''Full Screen'' button before clicking ''OK''. If the changes are undesirable then ''Cancel'' can be clicked. The ''Undo'' command can undo only the most recent accepted change to the image. Since all the raw images survive the stacking process unscathed then the image can be restacked and the process can be attempted again.
Very few of MaxIm's capabilities have been utilised so far. Future imagers are encouraged to experiment with producing 'pretty pictures'. Even changing the processing order may be beneficial to image production. Some suggestions are listed below.
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