Detecting added noise (partly OT) - Page 1
Forum section: electronics / general

author: Ultrapurple
author_rank: Super Contributor
timestamp: January 14, 2019, 09:54:45 am
content: I am aware of suggestions thatFLIR has been "caught" adding noiseto thermal images (though I have not read the original work on this). I would be interested to know if this goes on in other arenas.I have a DSLR with good performance, nevertheless, its image noise looks slightly odd. I can't quantify why; it just 'feels' different from other, earlier sensors from the same manufacturer. As far as I know the same (or very similar) sensor is used in several cameras and I suspect there will also be a 'new lower noise' version launched in a while. (Traditionally, DSLR manufacturers have more or less handpicked sensors for their top of the range cameras - I'm thinking Nikon D700 / D3, with the same sensor but the D3 had better performance, which I presume is because the vastly smaller number of sales - and higher price - made it worthwhile handpicking the best sensors and/or choosing those from a 'sweet spot' on the wafer).Call me cynical if you like, but if I had made a sensor that wasmuchbetter than today's generation I would be tempted to launch New Camera Mk 1 with better performance than its predecessor, but with theabsoluteperformance limited by added noise so I could launch a Mk 2 with even better performance without having to spend anything on sensor development.Now to the real question. How do we tell if artificial noise is being added?We can assume that the firmware is not accessible so it's impossible to reverse-engineer.We can also assume that the engineers are fairly smart and won't use a short-cycle pseudo random noise generator (PRNG).But, given a large enough (thousands?) sample of images, maybe all showing an identical scene, and access to the 'raw' sensor data (ie not jpg), is it feasible to analyse the data and differentiate between fixed pattern noise, genuine random noise, and added noise?My maths isn't good enough to do the analysis but I could probably understand the basic principles if someone leads me by the hand.Is there an expert in the house?

author: Whales
author_rank: Super Contributor
timestamp: January 14, 2019, 10:52:59 am
content: Find out exactly what physical phenomena are supposed to be creating the real noise floor of the sensor. See if this noise is white, pink, dependent on other things (gamma curve? regional light/IR intensity?), etc. Try and find something that makes the noise non-linear or non-symmetric. If I coded fake noise into software I'd probably be lazy and just make it a fixed symmetric/simple amount.

author: Vipitis
author_rank: Frequent Contributor
timestamp: January 14, 2019, 02:23:54 pm
content: okay, since you quoted me. I want to backup my claims.This thread:https://www.eevblog.com/forum/thermal-imaging/flir-one-thermal-imaging-camera-teardown-and-hacks/Post #2 and #8 talk about it in a FLIR One.And this thread:https://www.eevblog.com/forum/thermal-imaging/flir-e4-thermal-imaging-camera-teardown/msg342873/#msg342873there is different kinds of noise a sensor gets. And the biggest difference in DSLRs is the image processor and not the sensor. If you compare raw images and develop them in Lightroom or C1; you can see that the same sensor is still different.There is different ways to introduce real noise to your images and you can find a great example of how it is dealt with in astrophotography here:http://deepskystacker.free.fr/english/index.htmlFake noise is probably edit from a software part of the imaging pipeline and sometimes it's even used to conserve detail to force higher jpeg standars.