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I opened a FITs image data from TIRSPEC (NIR imaging) (an HgCdTe infrared imaging sensor) on DS9 and I saw that some of the bright stars have black patches at the center (negative values).

Can you please explain what this means?

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    $\begingroup$ I've got an answer prepared, but before I post, I'd like some more details. What is the source of the sky image? What telescope? What imaging technology (cmos, CCD, something made by NASA?) Also why do you tag "star-formation"? This has nothing to do with DS9 (that just displays the image) And everything to do with the telescope and imaging technology, so please tell us more about that. $\endgroup$
    – James K
    Oct 29, 2022 at 11:54
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    $\begingroup$ It's the data from TIRSPEC (NIR imaging). CCDs have been used to image. $\endgroup$
    – Rian
    Oct 31, 2022 at 9:11
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    $\begingroup$ Assuming it's this TIRSPEC, it's a Hawaii1K HgCdTe detector, not a CCD. $\endgroup$ Oct 31, 2022 at 12:46
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    $\begingroup$ My guess would be that the centers of the stars saturated the detector, and something in the post-processing translated that to negative counts. $\endgroup$ Oct 31, 2022 at 12:47
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    $\begingroup$ Yes you get the same thing with JWST images, it seems to be a feature of HgCdTe technology that it returns zero or negative values when oversaturated. $\endgroup$
    – James K
    Oct 31, 2022 at 17:49

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