“Andromeda’s Core using HDR Negative. 30Hrs total exposures”

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This is an image of the high dynamic range of the Andromeda Galaxy.
But it is said to be a negative HDR.
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In fact, it is not entirely negative. Only partial.
The clearer parts of the Andromeda Galaxy are darker and the darker parts are clearer.
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This is an HDR image shot in many different color ranges and is made in this format.
This is one of the tricks used to make visible parts that cannot be seen in visible light.