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Noise and colour banding in night photography help

Discussion in 'Photography & Video' started by Psilonaught, 16 Jan 2006.

  1. Psilonaught

    Mobster

    Joined: 20 Oct 2002

    Posts: 3,978

    Location: London Town

    I finally got some time to take my kit out for some night photography, and went to the South Bank last night - it was a full moon and I was pretty happy with my results (will post them in a seperate thread).

    The problem is that post RAW processing is showing quite a lot of noise and worse, some blotchiess and colour banding in the sky.

    The noise I can fix in Noiseware but the banding looks bad in some of them and will almost certainly be rejected by istock :(

    I always shoot ISO 100 and I have noticed the same noise and banding at 4sec and 30sec, so exposure time seems to make no difference

    I've tried playing around with CS2 RAW settings and luminous smoothing set to 99% seems to help but not much.

    The original raw image when viewed in the preview pane (pre-processing) doesn't seem to exhibit the same noise and banding??

    Any tips, suggestions??
     
  2. jhmaeng

    Wise Guy

    Joined: 6 May 2004

    Posts: 2,060

    Location: London, UK

    Banding tends to show up more when you push the exposure up in post. Did you expose to the right (well, the exposure you wanted anyway) when you actually took the shot, or are you doing the exp. comp in post?
     
  3. Psilonaught

    Mobster

    Joined: 20 Oct 2002

    Posts: 3,978

    Location: London Town

    on most of the shots I underexposed in the shot, and increased slightly in CS2. I also cooled down most of the images to reduce the orange glow from junk light in the clouds

    Are you saying that using post processing to increase exposure can cause these issues?
     
  4. hoodmeister

    Hitman

    Joined: 18 Sep 2005

    Posts: 932

    Location: Cardiff

    It can highlight the issues, yes.

    Try increasing the exposure of your shots in the field ;)
     
  5. jhmaeng

    Wise Guy

    Joined: 6 May 2004

    Posts: 2,060

    Location: London, UK

    Yup, if you push exposure of a night-time shot more than about +0.5ev, you are going to see whatever artifacts it generates even more clearly (and banding is one of them). That's why it's important to expose well in the first place, and this normally means setting your camera to about +1.0ev when you take the shot. You can normally overexpose in this way during the night because you're unlikely to get any clipping when the overall environment is so dark.
     
  6. Psilonaught

    Mobster

    Joined: 20 Oct 2002

    Posts: 3,978

    Location: London Town

    ok will take another look at the RAW images tonight and play around with the ones with higher exposures.

    Don't worry, I always bracket night shots, and I have a copy of each at a higher exposure ;)
     
  7. hoodmeister

    Hitman

    Joined: 18 Sep 2005

    Posts: 932

    Location: Cardiff

    Consider having a play with centre // spot metering with them, too.
     
  8. Psilonaught

    Mobster

    Joined: 20 Oct 2002

    Posts: 3,978

    Location: London Town

    guys what about mirror lock-up? Should I always be doing this when out at night with my tripod? Normally I set the camera to 10sec delay, focus, click and wait for the exposure.

    Thanks
     
  9. Cuchulain

    Sgarrista

    Joined: 28 Dec 2004

    Posts: 7,627

    Location: Derry

    For night shots I always use mirror lockup as I read (whether it's true or not is a different matter) that the mirror flicking back could move the camera slightly.
     
  10. Psilonaught

    Mobster

    Joined: 20 Oct 2002

    Posts: 3,978

    Location: London Town

    I found some more info about this on istock forum

    CCDs on most cameras will overheat and get qwirky grain problems on long exposures in low very light.

    the camera retains MORE information in the right side of the histogram than the left side. The rightmost one-third or one-quarter contains something like 3/4 or more of the image information. So you want to make sure that your mountain range is weighted to the right side, in effect. The histogram should look lopsided to the right side. Your subject, hopefully, should be as much as possible on the lighter side of middle tones


    interesting. Looks like my mistake was to use a high F stop and hence longer exposure, when in fact i should have been using a low F stop and shorter exposure.

    I also need to overexpose night images so the graph is right-sided
     
    Last edited: 16 Jan 2006
  11. jhmaeng

    Wise Guy

    Joined: 6 May 2004

    Posts: 2,060

    Location: London, UK

    But really, I'm not aware of any recent D-SLRs having problems with night exposures associated with overheating sensors.

    You need a reasonably small aperture in order to make sure everything remains sharp. Most people do ~30secs on a good tripod without any problems. Also, you should use lower ISO (unless you're trying to freeze action) because noise is particularly evident on darker colours.

    So in short, during the night: High-ish f-stop (enough to bring everything in focus), shutter time doesn't matter (up to a reasonable limit) and ISO should be as low as possible. As you said, the image should be exposed to the right.
     
  12. Psilonaught

    Mobster

    Joined: 20 Oct 2002

    Posts: 3,978

    Location: London Town

    yep that all makes sense - I did everything right apart from the over exposure part :rolleyes:

    WIll post the pics when I get home