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