Dual gain sensors (Dual Native ISO) - reducing noise at high ISOs

Ring-billed gull (left) and Foster's tern (right) photographed using my Z6iii camera

I am not well-versed in electronics and do not have a good understanding of the word "gain" as it applies to digital photo sensors.  So I have had to do some research on this to understand what exactly gain is and what a dual-gain sensor is.  

The voltage produced by electronic sensors that convert light into electricity is very low, and that's at a sensor's native ISO.  As ISO increases, those voltages become even lower.  The problem with high ISOs is that the background electronic noise that exists starts to interfere with the generated values produced, especially in shadows, which results in this thing we call noise.  I have written about this before (click here to see good examples on noise).

Gain is related to noise - the higher the ISO, the greater the need to boost the signal.  Boosting the signal (gain) results in brighter images (underexposed images from native ISO can be brightened by increasing the voltage - this is gain, the higher the ISO, the greater the gain).    All sensor data involves gain, but it is at a minimum level at native ISO (often an ISO of 100, but not always).  There is standard image processing that takes place at this level, and it is applied to every ISO boost thereafter.  The problem is that, as ISO increases, the signal becomes corrupted due to background noise.  Wouldn't it be nice is cameras had a way of processing the image at settings dedicated to those higher ISOs?

As it turns out, this is what a dual-gain sensor is all about.  At base and lower ISO levels, the camera's electronics process the information in one particular way.  However, when the ISO reaches a higher value, the camera switches the processing to a different circuit that helps to reduce noise.  A dual-gain sensor uses two different circuits to process the image, which one depends on the ISO.  In my Nikon Z6iii, the circuit switches over at an ISO of 800.  Before that, it uses the base process, at or above that, it engages the secondary system.  The result is less noise at high ISOs.

800% views of bird beaks from above image.  Notice there is less noise on the right.

Dual-gain sensors are relatively new.  For Nikon, cameras like the D850, D780, and D7500 use dual-gain technology.  All the Z series cameras use it.  Where the second circuit kicks in differs; for example, the D850 switches at an ISO of 400, while the D780 switches at 800.  It is worth your while to look into where the ISO switch is, as I can get less noise at 800 than I do at 640, or in the above shot, 500.  I will use an ISO of 800 more often.

Keep in mind that native ISO, or just above it, is a better choice for reducing noise.  But, if you need to use high shutter speeds in dim light, use an ISO that takes advantage of that second circuit, if your camera has one.

How do you know what cameras have dual-gain circuitry, and what ISO marks the transition?  I recommend doing a Google search using something like this:

Does my [camera name] have a dual gain sensor?  At what ISO does the second circuit engage?

I put this in Google (using Nikon Z6iii for camera name) and got this response:

Yes, the Nikon Z6 III features a dual-gain sensor. The second conversion gain circuit engages at ISO 800. [1]

Try it, you may be able to get better control over the noise issues you were having.

Thanks for reading.

Eric Svendsen     www.ericspix.com

Comments

Post a Comment

Popular posts from this blog

Harjit Bahia - Science teacher and colleague from Garibaldi died August 2, 2024

Image
You will be missed Mr. Bahia.  You made a difference and we are sad you are gone. I keep in loose contact with my fellow retired teachers from Garibaldi Secondary School.  I talked with my long-time friend, Mike Lynch, today, and discovered that Hargit died over the summer.  Unbeknownst to him, he had an underlying heart condition and passed away after working out on his treadmill.  The date was August 2, 2024. I was shocked to hear this.  He was only 49 years old, turning 50 some 3 months later.  It was a shock to everyone, for he was loved by all who knew him.  As a teacher, Mr. Bahia was kind and fun.  He contributed to students in many ways and was always available to help those in need.   For myself, I knew him as a fellow science teacher and taught in the adjoining room to him.  He was always available to help, share ideas, and work together.  Easy to approach, I found that I could talk to him about anything and appreciat...
Read more

The hard workers aboard the Ruby Princess

Image
A worker cleaning the Grand Hall at 3:00 in the morning I salute the hard working men and women of the cruise line industry.  They come from all over the world, each one looking to find work, possibly a career, and to help both themselves and their families have better lives.  It isn't easy, and many have to work long hours and are isolated from the passengers and passenger-areas aboard the ships.  They don't partake of the luxuries experienced by the guests and have a limited amount of free time.  But most of them wouldn't trade it for any other job they have ever had. I was photographing the Grand Hall aboard the Ruby Princess early in the morning before the place was crowded with guests.  While there, I met a gentleman cleaning floors and took some shots of him, asking permission first.  I also got quite a few photos of the hall itself without people; I used my 14-30 mm ultra-wide angle lens on a full-frame camera to get the three-story plaza in my viewf...
Read more

My longsuffering search for the Western Meadowlark

Image
Am I going to disturb a species I am photographing enough to negatively affect its relationship with the ecosystem?  This is an important ethical question that needs to be asked when looking to photograph a particular species.  And it's one that I don't think we do nearly often enough. I recognize the desire to capture remarkable images; I have been in search of premium photos the bulk of my adult life.  There is the personal connection - just the joy associated with doing something well and the praise we seek when others recognize it.  There is the professional connection - doing something as part of a job, assignment, or class.  Then there is the financial connection - the hope to win a contest, publish an image, or sell prints.   These are all worthy goals in their own right, but none of them should be the reason behind disturbing a species, especially ones that are endangered or are at a critical period in their life cycle.  Essentially it boi...
Read more