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Canon-Nebulosity Tutorial for Beginners - page 8 / 9





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the guess through all the frames. If you see a frame that has star movement, an airplane or a satellite, you can press “Shift + left click” to skip the frame. Time to take a break or mow the lawn or pull the weeds out of the garden as the laptop will now be doing some serious number crunching. When the stacking is finished, a window will appear and as before, name your object such as “TrifidStacked.” Be sure that it is being saved in the same “Trifid” folder. Press “Save.”

Now it’s time to bring out the detail. Under the “Image” menu, select “Adjust Color Background (offset)”. Don’t play with the sliders. Just click “DONE.” Again, this will require some number crunching so take another break.

Under the “Image” menu, select “Digital Development (DDP).” Our goal is an image that will be easy to process with PhotoShop or similar programs. At this point, we still have two problems:

  • 1.

    The midtones are too dark relative to the rest of the image; that is, the image needs gamma correction.

  • 2.

    Depending on whether they were stretched earlier, the pixel values may not use the full range (0 to 65, 535) of a 16-bit TIFF image.

A quick way to address both of these problems is called digital development. This is a combination of gamma correction and unsharp masking (sharpening). Digital development was invented by Kunihiko Okano. It is a rather quick algorithm to do what would otherwise be a multi-step process. In Nebulosity, the digital development algorithm usually works well with DSLR images. Just go to Digital Development (DDP), and let the algorithm do its work. We have had good results by simply pressing “Done.” Although the defaults are usually reasonable, you can further improve the image by adjusting the sliders; experiment with them.

Caution! Due to a bug in some Nebulosity programs, the sliders continue to sense movement after you release the mouse button. This can lead to confusing results. Immediately after moving a slider, do not move the mouse while the hourglass cursor in being displayed.

Now for a time-saving tip. Before selecting “Levels/Power Stretch in the next step, with the mouse, left click and hold down to crop a small portion of your image. During the Levels/Power Stretch, processing will only affect the cropped portion. At this point you probably don’t quite have a finished image. You can do some more stretching using the “Levels/Power Stretch” function. Under the “Image” menu, select “Levels/Power Stretch”. Some imagers suggest sliding the bottom slider left until you get a value of about 80. The middle slider should be moved about ¼ or 1/3 left. Finally, move the top slider to the apex of the histogram. This is where you can bring out additional detail and is the last step before post processing in a photo editing program such as “Microsoft Picture It!” or PhotoShop.

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