Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Measuring resolution by counting pixels

  • Please log in to reply
No replies to this topic

#1 Rickster

Rickster

    Apollo

  • *****
  • topic starter
  • Posts: 1,108
  • Joined: 09 Jun 2008
  • Loc: NC Kansas Bortle 3 SQM 21.8+

Posted 26 March 2020 - 01:07 PM

It occurred to me that I should be able to use pixels as a ruler, since I know the pixel scale (either from astrometry or from astronomy tools).  But I ran into problems.  It seems that something in my display is interpolating pixels such that when I zoom in, I never get to a level where I see individual pixels, unlike previous setups which would let me pixel peek by zooming in.  This is my home computer which is a Dell with an integrated 4k video card feeding a 50in 4k monitor. 

 

After exploring some options. I found that if I converted the image to TIF and viewed it in Windows Photo Viewer, the pixels were visible on screen.  Then I could snip the image off the screen and retain the pixelation.   This process looses clarity, but it is still good enough to get an idea.  Below is a snip of the M87 jet as an example.  The pixel scale is 0.27 arcsecond/pixel.  If rounded to 1/4 arcsecond/pixel for easy math, the jet width is about 2 arcseconds, depending on where you draw the boundary.  This compares favorably with published values. 

 

Note:  I trust posting this is in compliance with the rules in that I haven't post processed the image.  I have only zoomed in to the pixel level. If anyone has a better way to do this, please speak up.  The full image with details is located here https://www.cloudyni...ery/?p=10066727

Attached Thumbnails

  • snip m87.jpg

Edited by Rickster, 26 March 2020 - 01:09 PM.

  • mashirts and bdyer22 like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics