Examining the colors of stars and experimenting with different ways to portray this information.
The first photo is a star field in Pisces with the camera intentionally defocused. It's easier to see the color of dots than of very small points.
But a faint blue star looks rather gray/low saturation. Same for a yellow, orange, or red star.
Is there a way to artificially make all these star-color-dots the same brightness?
Yes, if you process the image in HSV color space instead of RGB color space.
https://en.wikipedia.org/wiki/HSL_and_HSV
https://en.wikipedia.org/wiki/RGB_color_model
The second photo is a re-processing of the first photo in HSV color space. I only manipulated the V (value) layer, which controls the brightness (not hue or saturation) of pixels. Below a certain threshold I set V = 0 to make it a black background and suppress the display of barely detected stars that are very noisy/grainy. Above that threshold I set V = 65% of max brightness.
Now all the star dots are the same brightness and it's easier to compare color between them. (But you have discarded brightness information, which makes it difficult to compare this image to a star atlas that shows brightness as different size dots.)
I can capture even more star 'color' information in the near infrared.
The third photo is a monochrome near IR image of the same star field.
But how can I compare this IR image to my color image?
The fourth image overlays the IR image with the color (visible light) image, but with a slight offset. You can see that blue stars tend to have rather faint IR images and the redder stars have brighter IR images. I have also put a green circle around a faint red star that has a very bright IR image. Looking at a star atlas, that is Z Piscium, which is a carbon star...very red to our eyes, and quite bright in IR.
https://www.wikidata.org/wiki/Q6170710
What other data visualization methods could I use to show star color?
#Stars #Astrophysics #Color #Spectrum #Infrared #Monochrome #Photography #Science #Art
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