1. Reminder: Please use our affiliate links for holiday shopping!

Need some pointer on noise reduction for time lapse

Discussion in 'Astrophotography' started by tg9413, Jul 31, 2016.

  1. tg9413

    tg9413 Mu-43 Regular

    76
    Mar 12, 2014
    Hi all,
    I need some pointer to the right tools for doing noise reduction for my first time lapse try. I took about 300 frames of milky way, with 2000 iso and 15s SS with my GX7 + pana lecia 15mm. the images are alright, got enough detail to make out pretty obvious milky way and with some brushing I can get a pretty decent picture. But since I turned Long exposure NR off during shots, the noise in each frame is pretty bad, a lot of red pixels along the edge of the frame edge.

    I did some research on my own, and pretty much all the people are suggesting to do stacking for noise reduction, but all the tuts or posts I can find seems focus on stacking to get a perfect single frame out. I can't seem to find any information regarding how to get a so-called average hot spots map and apply them to all the frames in the time lapse. is it this something doable on raw or I have to export them to jpg and work form there?
    Also I probably want to do some local brushing in LR to give the milky way a more yellow/purplish looking, is there any tool I can just apply the brush to one frame and automated process across all frames as the milky way go across the sky?

    Thank you very much for the helps in advance!
     
  2. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    157
    Dec 18, 2015
    Alex S.
    Deep sky stacker supports raw files if i recall correctly, if you have already aligned your frames, you can also just bring all the raws into photoshop as layers, select them all, create a smart object from them and then set the stacking mode to median (average out pixels)
    I don't know if this is something you can do in lightroom as I don't own it

    For the hot/stuck pixels, i recommend just clone stamping from the area around them, there usually aren't too many and i found that automated processes in post-pro don't really do a good job in my opinion

    As for adding color/punch to your milkyway, you don't do this before stacking, you do it afterwards as you're only introducing another layer for error, so combine your frames first and /then/ start working on retouching ;)

    Edit: if i misunderstood your post and all those 300 images are supposed to be final results, you should have talen a dark frame (photo with lens cap on) with the same settings as the milkyway shots, these can be used to easily locate hot pixels, there might also be a way to find them using multiple frames and some blending modes in photoshop but i have no experience on that area so will leave it to others on here :)
     
  3. wjiang

    wjiang Mu-43 Hall of Famer

    What you're looking for is dark frame subtraction. You can do it after the fact to some extent, just take a series of shots with the lens cap on at the same temperature, ISO and shutter speed as the original shots. These blank shots are are dark frames, while your originals with information are the light frames. Software like DeepSkyStacker can take the dark frames and isolate the hot pixels, then remove then from your light frames.

    This sounds somewhat awful to do in a stills-oriented software like LR, as the Milky Way will be constantly moving across the frame... if the overall movement isn't too much you can probably apply the same adjustments to each file, otherwise you might have to use something like the motion features in PS:
     
  4. tg9413

    tg9413 Mu-43 Regular

    76
    Mar 12, 2014
    Thanks for the tips. It was stupid on my part that I forgot to take any dark frame that night. Guess it was at 3am and after a full day of work my brain just wasn't functioning properly. I will try to use the same SS and iso to take some darkframe now to see if I can get rid some of the major hot spots. Here is one of the shot from that night with long exposure noise reduction and some PP... hopefully I can get something similar with the ones without the NR :x
     

    Attached Files:

    • Like Like x 2
  5. AG_Alex2097

    AG_Alex2097 Mu-43 Regular

    157
    Dec 18, 2015
    Alex S.
    I'd be really interested to see you stack some of those, they already look really nice, but there is indeed a high amount of coloured noise (even with the LEN reduction), stacking is probably going to give you the best result, regardless of a dark frame or not (in my experience, dark frames are mostly useful for hot/stuck pixels rather than noise), i doubt the dark frames you have taken now will give you the same result like they would have during the shoot (it is recommended you take multiple dark frames over the course of your shoot as the output changes every time (if only a little))
    Here's a good read on all the kinds of things you can do to improve your astro shooting: Starizona's Guide to CCD Imaging

    Really like your second shot btw :)
     
  6. tg9413

    tg9413 Mu-43 Regular

    76
    Mar 12, 2014

    this is best i came up with after fiddling with different methods i dug up online to reduce noise. The image is actually quiet blurry from over processed, and it is still pretty bad around the edge of the frame, and to make things worse when the actual star are moving, you can see bunch of white spots that would just seem like a star in a still photo but totally not moving in a time lapse :rofl:
    This sure teach me a good lesson on the importance of taking dark frames :x

    Thanks guys for all the helps.
     
    • Like Like x 2