1 | Introduction
2 | The Basic Process
3 | Image Processing Programs
4 | Artifacts
5 | Related Links
Common ‘artifacts’ that you may find in WISE images
Some of the images downloaded directly from the WISE archive will have obvious ‘artifacts’ or ‘defects’. These are parts of the image that do not accurately show what is actually out in space, but instead are created by the telescope’s optics or detectors. They’re typically found in or near very bright objects. There are many types of artifacts, but for the purposes of making color pictures there are 3 that are the most important to be aware of. Removing these artifacts from the images typically involves advanced image processing techniques that we won’t explain here, but it’s often helpful to be able to recognize them:
These will appear as dark holes in the middle of bright objects. They’re created when certain pixels in the detector ‘overflow’ with too many photons. Think of them as places where the object was so bright that it overwhelmed the camera. An easy amateur fix for these is to ‘paint’ in white pixels to fill in the holes.
These will appear as bright spots surrounded by dark halos. They’re places where the camera had not yet recovered from the previous picture it took. The pixels in that part of the camera were still ‘warm’ from a bright object that hit the detector in the same spot during the previous image.
These will look like little rings. They often appear multiple times in one image, always in the same position relative to nearby bright stars. The brightness of the ghost varies with the parent star, but the size of the ghost does not. They’re caused by internal reflections inside the space telescope.
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