So, where are the stars?

In my pre­vi­ous rant about dynam­ic expo­sure in Elite Dan­ger­ous (which hon­est­ly applies to any oth­er space game made to date), I made a rough cal­cu­la­tion to pre­dict the bright­ness of stars as they should real­is­ti­cal­ly appear in pho­tos tak­en in out­er space. My pre­dic­tion was, that,

  • for an illu­mi­na­tion of sim­i­lar strength to that on earth,
  • if the sun­lit parts are prop­er­ly exposed,
  • and with an angu­lar res­o­lu­tion of about 2 arc min­utes per pixel,

then the pix­el-val­ue of a promi­nent star should be in the order of 1 to 3 (out of 255, in 8‑bit sRGB encod­ing). Since then I was curi­ous to find some real world val­i­da­tion for that fact, and it seems I have now found it.


The pho­to above was tak­en from here, and is of such an excep­tion­al qual­i­ty that it can be bright­ened by more than 100 times with­out show­ing any vis­i­ble bloom or glare effects. Now, where are the stars? Where indeed, just add about +11 EV (and sub­tract the slight black level):

ISS_and_Endeavour_EV+11In the orig­i­nal pho­to, the pix­el val­ue of the bright­est stars are in the 20%-range; how­ev­er that pho­to has a crazy res­o­lu­tion where a sin­gle pix­el is like­ly to rep­re­sent much less than one arc sec­ond. If the pho­to is down­scaled to web res­o­lu­tion (as shown above), then the RGB val­ues of stars indeed turn out to be around 5 (out of 255).

And while I am at it, check out these amaz­ing videos of space walk footage tak­en with a real cam­era, which con­tains count­less exam­ples of real-world (or real-space?) illu­mi­na­tion situations!

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