UKH

A couple of nights ago I went to Llanddwyn Island, just off the Isle of Anglesey to capture images of the Milky Way and Perseids meteors.

I had a great night with my Panasonic GH5 and Lowa 7.5mm manual prime lens. I have included two sample shots of the night which show the Hot Pixels in the dark areas. I tried to experiment with ISO Invariance to see if this would help. I don't have any Dark Frames for the simple reason that I forgot to take any. The shots may be a bit soft. It was a very windy night with a lot of sea spray in the air and I forgot my lens cloth. Doh!

I would be grateful for any help, tips advice or software that will help me to eliminate the Hot Pixels

Shot one was taken at ISO 5000

Shot two was taken at ISO 800

Both images were edited in Lightroom 5. Yep the old version because I'm a cheapskate and won't pay monthly for Lightroom.

https://www.flickr.com/photos/the1lemming/51378396366/in/dateposted-public/

https://www.flickr.com/photos/the1lemming/51377632042/in/dateposted-public/

Nice shots!

I take it these are single shots rather than stacked? I’d just use the clone stamp tool, and a bit of patience. I’m sure there are other ways too.

There are other techniques (practical and software based) that will help to eliminate hot pixels without using dark frames, such as dithering and cosmetic correction. Both require multiple exposures though, and different software than just lightroom.

Hot pixels vary somewhat over time, but not quickly, so you should be able to take a dark frame now and use it with an image taken a few days ago. Make sure all the camera settings are the same and that the camera temperature is about the same. The dark frame will increase noise a bit, but you can mitigate that a bit by stacking (averaging) say 8 dark frames before subtracting it from the image. Sadly, the Panasonic sensor seems pretty poor for hot pixels at anything resembling long exposures.

Is there an in-camera function for removing them? Olympus ones have it.

That’s why I love my Olympus - loads of magic features 🤣

nice images. 

id agree with dark frames too. Affinity offers a great stacking tool if you want to part with a few quick for that, plus many other features that Lightroom does (though a bit of getting used too) 

if you time it right, you can get it for around £30 

The tools I use for astrophotography are all free and are...

Astrophotographytool (APT) - for collecting subs, controlling the camera, making sure focus is spot on etc

Deepskystacker (DSS) - for checking each sub, registering and stacking

GIMP - free version of photoshop - probably not as functional but it's good enough for me. 

If you're simply shooting a load of photos manually then shoot in RAW and you can dispense with APT (or equivalent).  Do try to collect a load of dark frames at the same temp, ISO and exposure time as your light frames. they'll make all the difference. 

If the dark frame issues are based on your sensor, no reason you couldn't take them now. For my sciency stuff I use ImageJ (or Fiji - Fiji Is Just ImageJ) - lots of fantastic plug-ins.

For a hot pixel you could use the median of the surrounding pixels (but that would need a dark frame) 

Lemming's GH5 does have such a function, but you have to enable it BEFORE you take the picture, not several days after

For what Lemming wanted to do (in this case) you don't needs any AP tools. You can average several darks using 'normal blend' and then subtract the result from the original image with a 'difference blend'. The fancier tools earn their keep when you start doing 'proper' stacking, but that's a different ball-game (need a tracker* for a start).

* OK, I know. You don't strictly speaking. You can stack untracked images, but that comes with it's own set of non-trivial complications.

You need to spray them with a hot pixel extinguisher. They're difficult to find, and charged with cold pixels...

Luckily for you, I have a spare one that I'm willing to sell to you for only £150. Let me know. 

Yes, but I don't like noise reduction. I want my images now. NOW I TELL YOU. 😀

Here's a stacked image with me going crazy on the spot removal tool.

https://www.flickr.com/photos/the1lemming/51383944617/in/dateposted-public/

Yeah the Panasonic G9 has it, basically takes a dark frame shot of the equal exposure and subtracts any hot pixels from the initial exposure, well that’s how I imagine it works !

It’s a bit of a pain when you are stood out in the cold but seems to work.

The best way to deal with hot pixels is to announce that you have discovered a new star.

I have found 3 supernovae, 5 planets and a dozen asteroids in the last 6 months and didn't even need to buy a telescope.

It's generally better to shoot without using the 'Long Exposure NR' mode, take some dark frames separately (typically once it starts getting light), stack them into a 'master dark' and then apply that to each of the light frames before stacking the light frames. It results in less overall noise (for a given number of frames) and it means you can use your precious time in the dark (and cold) to get more useful light frames (and reduce noise by another factor of 1.4). Not a massive difference, but it all helps.