Digitsl noise and ‘hot pixels’

Guest2 · 30 Apr 2022 at 22:49

Is this correct?

The jpg photos most likely were processed in camera for noise reduction.

The raw photos, being relatively unprocessed in camera, would need some sort of noise reduction in software.

Long exposure photos produce quite a bit of digital noise and "hot pixels" that needs to be addressed in software.

Even brand new cameras produce this type of digital noise, so it's not a defect with your camera.

Red, Green, and Purple Dots in My RAW Photos: Canon EOS 7D / 10D - 90D Talk Forum: Digital Photography Review

Expert news, reviews and videos of the latest digital cameras, lenses, accessories, and phones. Get answers to your questions in our photography forums.

www.dpreview.com

Viewing RAW data I see two red and one green pixel on most photos (but not all) opening on Win10 photo viewer they are not seen - I expect as they’re automatically processed and removed.

Example below is a snip of a RAW pic.

Buddy · 2 May 2022 at 12:23

Did you increase the exposure in post for an under-exposed image? You can get these sort of artefacts with a noisy image if you did this.

Either expose to the right and make sure you avoid clipping of highlight or use software like Denoise in post to reduce noise.

I've found various issues with windows photo viewer. You need to make sure your colour profile from camera through to software is the same throughout.

Guest2 · 3 May 2022 at 17:46

Buddy said:
Did you increase the exposure in post for an under-exposed image? You can get these sort of artefacts with a noisy image if you did this.

Either expose to the right and make sure you avoid clipping of highlight or use software like Denoise in post to reduce noise.

I've found various issues with windows photo viewer. You need to make sure your colour profile from camera through to software is the same throughout.

Ive looked again and the same pixels appear on all photos, just harder to see on lower ISO and brighter photos.
This is 800ISO, 1000% zoom on a RAW image

No post processing of exposure is being carried out. How do I check colour profile from camera to software?

Thanks

Kenai · 3 May 2022 at 18:04

Are you getting this on all images or only long exposures?

Typically 'hot pixels' will only show on long exposures (due to the sensor getting hot).

If it's on all pictures, it's more likely 'stuck pixels' which will consistently show up as a particular colour - they sometimes go away in time, new ones might appear. They're a relatively common occurrence though - depending on the camera it may even have some settings to automatically map them out in camera.

Guest2 · 3 May 2022 at 20:05

Kenai said:
Are you getting this on all images or only long exposures?

Typically 'hot pixels' will only show on long exposures (due to the sensor getting hot).

If it's on all pictures, it's more likely 'stuck pixels' which will consistently show up as a particular colour - they sometimes go away in time, new ones might appear. They're a relatively common occurrence though - depending on the camera it may even have some settings to automatically map them out in camera.

All pictures, just the lower ISO ones its harder to see them as they are more faint.
Camera is a Canon EOS 550D

Kenai · 3 May 2022 at 20:21

A quick google suggests there's a process you can try that may eliminate them, I won't recommend any specific sites as I don't know Canon gear all that well to know which is best.

Google 'eos 550D stuck pixels' and there's all sorts of links about some sort of 'manual cleaning' operation in the camera menu that can be used to try and alleviate the problem.

Failing that, what software are you using to process the RAW images? You may be able to map them out there.

Guest2 · 3 May 2022 at 23:20

Kenai said:
A quick google suggests there's a process you can try that may eliminate them, I won't recommend any specific sites as I don't know Canon gear all that well to know which is best.

Google 'eos 550D stuck pixels' and there's all sorts of links about some sort of 'manual cleaning' operation in the camera menu that can be used to try and alleviate the problem.

Failing that, what software are you using to process the RAW images? You may be able to map them out there.

I found some info and ran a manual clean but simply selecting manual clean and leaving it for 5 minutes before powering off. It seems to have help a bit but will test more tomrrow, thanks.
When I went into Jessops they instantly said "The sensor is faulty" I find it hard to believe though, what being so much information online about digital noise, hot pixels, remapping pixels and the like.
I'm just using 'fastrawviewer' to open images. In Win10 photos the red pixels do not appear to guess its running some sort of 'dust and scratches' removal process similar to what is in Photoshop. Using Photoshop, that filter can easily remove them but wanted to confirm its not the sensor.

Astrophotography but be nightmare, taking super long exposure shots would probably pick up these red/green/blue pixles instead "wow, i've found a new planet..." nope, just another hot pixel instead of a sun!