Blink comparators were invented to make searching photographs of sky images, taken on different nights, for novas, variable stars or planets/asteroids, more efficient. The comparator would show first one image and then the other, rapidly, and any change in the image would stand out to the user. Asteroids would appear to “jump” from one location to another. Variable stars would shrink and swell. Novas would blink in and out.
Originally complex mechanical devices using glass plates, blink comparators are now found in astronomical image processing software, such as:
GAIA – Graphical Astronomy and Image Analysis Tool.
From the webpage:
GAIA is an highly interactive image display tool but with the additional capability of being extendable to integrate other programs and to manipulate and display data-cubes. At present image analysis extensions are provided that cover the astronomically interesting areas of aperture & optimal photometry, automatic source detection, surface photometry, contouring, arbitrary region analysis, celestial coordinate readout, calibration and modification, grid overlays, blink comparison, image defect patching, polarization vector plotting and the ability to connect to resources available in Virtual Observatory catalogues and image archives, as well as the older Skycat formats.
GAIA also features tools for interactively displaying image planes from data-cubes and plotting spectra extracted from the third dimension. It can also display 3D visualisations of data-cubes using iso-surfaces and volume rendering.
It’s capabilities include:
- Image Display Capabilities
- Display of images in FITS and Starlink NDF formats.
- Panning, zooming, data range and colour table changes.
- Continuous display of the cursor position and image data value.
- Display of many images.
- Annotation, using text and line graphics (boxes, circles, polygons, lines with arrowheads, ellipses…).
- Real time pixel value table.
- Display of image planes from data cubes.
- Display of point and region spectra extracted from cubes.
- Display of images and catalogues from SAMP-aware applications.
- Selection of 2D or 3D regions using an integer mask.
- Image Analysis Capabilities
- Aperture photometry.
- Optimal photometry.
- Automated object detection.
- Extended surface photometry.
- Image patching.
- Arbitrary shaped region analysis.
- Polarization vector plotting and manipulation.
- Blink comparison of displayed images.
- Interactive position marking.
- Celestial co-ordinates readout.
- Astrometric calibration.
- Astrometric grid overlay.
- Celestial co-ordinate system selection.
- Sky co-ordinate offsets.
- Real time profiling.
- Object parameterization.
- Catalogue Capabilities
- VO capabilities
- Cone search queries
- Simple image access queries
- Skycat capabilities
- Plot positions in your field from a range of on-line catalogues (various, including HST guide stars).
- Query databases about objects in field (NED and SIMBAD).
- Display images of any region of sky (Digital Sky Survey).
- Query archives of any observations available for a region of sky (HST, NTT and CFHT).
- Display positions from local catalogues (allows selection and fine control over appearance of positions).
- 3D Cube Handling
- Display of image slices from NDF and FITS cubes.
- Continuous extraction and display of spectra.
- Collapsing, animation, detrending, filtering.
- 3D visualisation with iso-surfaces and volume rendering.
- Celestial, spectral and time coordinate handling.
- CUPID catalogues and masks
- Display catalogues in 2 or 3D
- Display selected regions of masks in 2 or 3D
With a blink comparator, when offered an image you can quickly “proof” it against an earlier image of the same scene, looking for any enhancements or changes.
Moreover, if you have drone-based photo-reconnaissance images, a tool like GAIA will give you the capability to quickly compare them to other images.
I am hopeful you will also use this as an opportunity to explore the processing of astronomical images, which is an innocent enough explanation for powerful image processing software on your computer.