Blink Comparator app for iPhone and iPad

Blink Comparator is an app dedicated to Amateur Astronomers who like to take pictures of the Night Sky. It allows to compare two images of the same area taken at different times, to see if there are changes,  highlighted by the blinking of any object (star, asteroid, etc.) that only appears in one of the images or that  changed position or brightness between a shot and the other.
 
After shooting pictures of stars clusters, nebulae, galaxies and so on, often you would check if there are changes compared to the “normal" appearance of the photographed area.
 To do it, usually you have to search for a picture (or map) of the same area and check brightness and location of each object.
Unless you have a blink comparator that, alternating the vision of two shots obtained at different times, allows to detect and highlight changes or transient phenomena (comets, variable stars, novae and supernovae, asteroids etc.). In the comparator, the sample image and the reference are shown alternately after being aligned with each other. If an object is present in only one of the pictures,  it blinks and can be easily found and marked. Instead, if an object has changed position between two consecutive shots, during the animation it bounces back and forth, showing the path traveled.
The app  allows you to carry in your pocket this simple tool, using it  even during the shooting sessions for live checking.
 
With "Blink Comparator" you can:
 
- load pictures from the local Photo Gallery or from Dropbox;
- easily align the two images: just mark the same three stars on each picture and press a button:  the sample image is rotated, resized and moved to overlap the reference picture
- set blinking time interval
- zoom and pan the animation to frame a specific area or to examine in detail the images
- insert a mark to highlight an object
- add a label to describe  subject,  date and time of shooting etc.
- save animations as short movies  in your local Photo Gallery
- save movies converted to negative too