Lunar animations: Aligning images
in [DSP]
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From: Clay on 28 Dec 2009 11:21 On Dec 26, 10:57 am, Rune Allnor <all...(a)tele.ntnu.no> wrote: > Hi all. > > The past few days the moon has been unusually visible (that is, > visible for an unusally long consecutive time), so that the change > in phase is clearly visible over the course of a few hours. > > The idea occured to me that it ought to be possible to take a number > of images of the moon, with a few hours interval, and assemble some > sort of animation of the lunar cycle from these images. > > For this to work, one would need to align the individual images > to some reference image frame. My telescope is of the 'terrestial' > type, which means the tripod is oriented with respect to the horizon, > not the earth's axis of rotation, which causes all kinds of alignment > problems. Since such a sequence of images by necessity must be > taken over the course of considerable time (at least hours and days, > preferably weeks, probably months and years), one can not rely on > fixed references or constant system settings. > > So there will be a considerable amount of fiddling required > to align the images. > > What I have in mind is something like: > > 1) Take the image > 2) Adjust brightness > 3) Apply a Canny edge detector > 4) Use the edge image to find translation/scale/rotation parameters > relative to an overall reference frame > 5) Scale/rotate/translate original image according to parameters > from step 4) > 6) Crop/resample the original image to a reference resolution > 7) Insert into to existing sequence of images > 8) (Re)generate animation > > The difficult steps here are items 4) and 5), first finding scale and > rotation parameters and then scaling and rotating each individual > image reative to the reference. > > Do anyone know how to do these kinds of things? I do *not* have > access to any image processing software packages. Since there > are less than 40 clear-weather winter nights per year and the moon > is below the horizon in summer, most of the fun of this project would > be to implement the algorithms... > > Rune Related to your problem but not the solutions for making movies is RegiStax. This freeware is used by many astrophotographers for stacking images to create clean images. Essentailly one takes tens to hundreds of images of a single subject. And the then program sorts them by image detail content (uses Fourier Transform), aligns (translates and rotates) the images and then puts then on top of each other so as to reduce noise. When doing planetary astrophotography, one often uses a webcam to collects thousands of frames. Yes you record a movie of the planet. Since you need high magnification (200 to 1000x is not unusual) the atmospheric jitter is quite apparent. But most of the time the planet appears stationary for each 1/60 sec. exposure. But during some of the exposures the image jumps quite a bit. So RegiStax works well to sort these images and create a good final. I thought you would like to try to image the moon and combine them. Clay |