We have been working to reduce the number of false-positive detections from magic in GPC1 images.

We spent several days this past week improving the static mask, and this has had an important effect on improving the quality of the magic analysis. Unfortunately, it is not a complete or sufficient solution.

The following images illustrate the effects which are triggering magic false positives:

The first two images show the streaks identified by magic in an example image:

The image on the right shows the locations of features detected by magic. The green regions are the actual contributing pixels while the black bands show the determined boundaries of the full streak (a streak may only be detected in a small number of segments). The image on the left shows a greyscale jpeg of the full exposure, rotated and cropped to match the streak detection image on the right.

First, there is only a single real satellite streak in this image, and it is easily detected. However, there are many false positives. It is clear from their orientation along the camera rows and/or columns that most of the false streaks are due to artifacts in the image associated with the camera structures. A closer examination reveals several types of artifacts. Three regions are marked in the greyscale image. Below, we show some images to illustrates these effects more closely:

1) tiltystreak artifacts:

2) glints:

3) Other structures:

These two images illustrate two types of artifacts: persistent charge and glow structures. The image on the right is the raw image used in the analysis above. The image on the left shows the same pixel region for a different image, in this case one of a number of short g-band exposures used to improve the static masking. This illustrates the challenge of masking the glow / dark structures in these images: The glow structures change significantly from image to image.