What about dual gain

Started Jul 17, 2018 | Questions
Deursen Regular Member • Posts: 209
What about dual gain
1

Maybe a stupid question, but what is the dual gain doing for picture quality.

At ISO 640 a second amp is used to increase low ISO performance. Since the noise is coming from the sensor this also means that the noise is amplified more is suppose.

What is the best strategy to use when shooting around ISO 640? Say ISO is 400 would it be best to manually switch to ISO 640 to let the camera switch to the second gain amplifier? Or keep ISO below 640 and do post processing?

I read about it and saw the comments about bit depths, but what would be the best strategy?

 Deursen's gear list:Deursen's gear list
Sony a7 II Sony a7R III Sony 135mm F2.8 (T4.5) STF Sony FE 55mm F1.8 Zeiss Batis 85mm F1.8 +3 more
ANSWER:
This question has not been answered yet.
slstr Senior Member • Posts: 1,031
Re: What about dual gain
1

Deursen wrote:

Maybe a stupid question, but what is the dual gain doing for picture quality.

Assuming A7r2,A9, A7r3 etc.. Lower read noise at ISO 640 compared to ISO 100, and you pay with lower full well capacity resulting in less engineering dynamic range than at iso 100 .. as long as I am not overexposing important highlights this is a trade I am willing to make.

A7S was introduced earlier and switches at higher ISO, here are some details regarding the dual gain technology .. http://www.photonstophotos.net/GeneralTopics/Sensors_&_Raw/Sony_A7S_DR-Pix_Read_Noise.htm

At ISO 640 a second amp is used to increase low ISO performance. Since the noise is coming from the sensor this also means that the noise is amplified more is suppose.

Hi gain mode at iso 640 and above gets you lower read noise.

What is the best strategy to use when shooting around ISO 640? Say ISO is 400 would it be best to manually switch to ISO 640 to let the camera switch to the second gain amplifier? Or keep ISO below 640 and do post processing?

ISO 400 on A7R2, A9, A7R3, A7iii is suboptimal, use ISO100 to protect highlights or ISO640 to minimize read noise.

I read about it and saw the comments about bit depths, but what would be the best strategy?

For details i recommend reading these posts by Jim Kasson (his blog is a great resource.)

https://www.dpreview.com/forums/post/59077711

https://blog.kasson.com/the-last-word/cruising-with-the-sony-a7rii-exposure-strategy/

In my case ISO 640 is great for indoors or post-sunset pictures (street/event/conerts etc.. ) when I am mostly limited in shutter speed by subject movement and want to keep shutter speed higher than 1/160s or so ..

At ISO 640 the lower bit depth some shutter and/or drive modes makes very little difference, so when in at ISO 640 or higher I don't worry about bit depth.

In some (rare) cases the use of lossy compressed vs uncompressed lossless raw can make a difference
https://www.dpreview.com/articles/6144418951/what-difference-does-it-make-sony-uncompressed-raw

https://www.dpreview.com/forums/thread/4299737

I have seen these compression artifacts in my work when using compressed raw and for instance backlit faces/limbs/edges against brighter background, these hi contrast transitions can result in visible artifacts when i push shadow detail .. It's not something I worry about as the solution is easy. Either use uncompressed raw to prevent, or digital tool in post processing, such as http://aggregate.org/DIT/KARWY/

What camera(s) do you have in mind ? there are slight differences between A7x and A9 cameras as to what bit depth they have in different shutter and drive modes etc..

 slstr's gear list:slstr's gear list
Sony a7S Sony a7 II Sony a7R II Sony a9 Sony E 30mm F3.5 Macro +12 more
Entropy512 Veteran Member • Posts: 4,819
Re: What about dual gain
2

Deursen wrote:

Maybe a stupid question, but what is the dual gain doing for picture quality.

At ISO 640 a second amp is used to increase low ISO performance. Since the noise is coming from the sensor this also means that the noise is amplified more is suppose.

What is the best strategy to use when shooting around ISO 640? Say ISO is 400 would it be best to manually switch to ISO 640 to let the camera switch to the second gain amplifier? Or keep ISO below 640 and do post processing?

I read about it and saw the comments about bit depths, but what would be the best strategy?

It's not quite a second amp - it's actually, if I recall correctly, that a capacitor is put into parallel with the photosite to increase FWC at low ISO.  However, this capacitor increases noise.  (It's just that you get higher DR at ISO100 despite the extra noise because of the significant increase in FWC provides more benefit than the drawback.

Above 640, the capacitor is removed.  FWC is reduced significantly, but read noise is reduced by even more.

-- hide signature --

Context is key. If I have quoted someone else's post when replying, please do not reply to something I say without reading text that I have quoted, and understanding the reason the quote function exists.

 Entropy512's gear list:Entropy512's gear list
Sony a6000 Pentax K-5 Pentax K-01 Sony a6300 Canon EF 85mm F1.8 USM +5 more
JimKasson
JimKasson Forum Pro • Posts: 28,999
Re: What about dual gain
3

Entropy512 wrote:

Deursen wrote:

Maybe a stupid question, but what is the dual gain doing for picture quality.

At ISO 640 a second amp is used to increase low ISO performance. Since the noise is coming from the sensor this also means that the noise is amplified more is suppose.

What is the best strategy to use when shooting around ISO 640? Say ISO is 400 would it be best to manually switch to ISO 640 to let the camera switch to the second gain amplifier? Or keep ISO below 640 and do post processing?

I read about it and saw the comments about bit depths, but what would be the best strategy?

It's not quite a second amp - it's actually, if I recall correctly, that a capacitor is put into parallel with the photosite to increase FWC at low ISO. However, this capacitor increases noise. (It's just that you get higher DR at ISO100 despite the extra noise because of the significant increase in FWC provides more benefit than the drawback.

Good explanation. A point of clarification. When the capacitor is in place, the read noise in volts is not materially affected, but, since the conversion gain (voltage divided by charge) is lowered when the cap is in parallel with the photodiode, the read noise in electrons is worse.

Above 640, the capacitor is removed. FWC is reduced significantly, but read noise

in electrons (input-referred read noise).

is reduced by even more.

Jim

-- hide signature --
 JimKasson's gear list:JimKasson's gear list
Nikon D5 Sony a7 III Nikon Z7 Fujifilm GFX 100 Sony a7R IV +2 more
sabin_csl Forum Member • Posts: 69
Re: What about dual gain

Deursen wrote:

Maybe a stupid question, but what is the dual gain doing for picture quality.

At iso 640 you get better DR and that improve the quality of the pictures from 640 and up,as oppose to sony not implementing it. The noise will still increase as you go higher in the iso range.

You don't have to stress or think about it, maybe if you shoot at iso 400 500 and think that you need to increase the exposure in post even just the shadow you might want to go to 640 and overexpose a little and that gives you a little cleaner shadow. But tipically don't even think about it. Just know that it's a better quality at the end than it would have been without it

(unknown member) Senior Member • Posts: 8,068
Re: What about dual gain
1

Do you always shoot at ISO 100 or ISO 640 and do the rest in post for your work? Just curious what is the best practical use.

sabin_csl Forum Member • Posts: 69
Re: What about dual gain

Deursen wrote

At ISO 640 a second amp is used to increase low ISO performance.

You mean HIGH ISO performance. The second stage is used to give you better quality at higher iso than without it.

Personally I don't care about ISO. Just when I am around 400 I go to 640 and over expose a little. Because the way I shoot I usually get the shadow up more in post, because I mainly shoot people. And if I overexpose like 0.3 or even 0.7 ev from 400 or 500 to 640 keeping the aperture and sjutter speed the same I found out that I have better shadow, I mean the noise is lower in the shadows after edit. And I can easily recover from raw that small over exposure even in the highlights I normally don't notice any difference.

I care more about the pose, expression, the right moment, light and shaddow,  focus etc then I care about ISO.

JimKasson
JimKasson Forum Pro • Posts: 28,999
Re: What about dual gain

BBQue wrote:

Do you always shoot at ISO 100 or ISO 640 and do the rest in post for your work? Just curious what is the best practical use.

Not always. More often than not, though.

Take a look at this:

https://blog.kasson.com/d850/d850-exposure-strategy-manual-settings/

If you scale the ISO setting by 2/3 of a stop, that works for the a7RIII.

Jim

-- hide signature --
 JimKasson's gear list:JimKasson's gear list
Nikon D5 Sony a7 III Nikon Z7 Fujifilm GFX 100 Sony a7R IV +2 more
JimKasson
JimKasson Forum Pro • Posts: 28,999
Re: What about dual gain

sabin_csl wrote:

Deursen wrote

At ISO 640 a second amp is used to increase low ISO performance.

You mean HIGH ISO performance. The second stage is used to give you better quality at higher iso than without it.

There is no second stage.

That's already been pointed out.

https://www.dpreview.com/forums/post/61385233

Personally I don't care about ISO. Just when I am around 400 I go to 640 and over expose a little. Because the way I shoot I usually get the shadow up more in post, because I mainly shoot people. And if I overexpose like 0.3 or even 0.7 ev from 400 or 500 to 640 keeping the aperture and sjutter speed the same I found out that I have better shadow, I mean the noise is lower in the shadows after edit. And I can easily recover from raw that small over exposure even in the highlights I normally don't notice any difference.

I care more about the pose, expression, the right moment, light and shaddow, focus etc then I care about ISO.

-- hide signature --
 JimKasson's gear list:JimKasson's gear list
Nikon D5 Sony a7 III Nikon Z7 Fujifilm GFX 100 Sony a7R IV +2 more
(unknown member) Senior Member • Posts: 8,068
Re: What about dual gain
1

JimKasson wrote:

BBQue wrote:

Do you always shoot at ISO 100 or ISO 640 and do the rest in post for your work? Just curious what is the best practical use.

Not always. More often than not, though.

Take a look at this:

https://blog.kasson.com/d850/d850-exposure-strategy-manual-settings/

If you scale the ISO setting by 2/3 of a stop, that works for the a7RIII.

Jim

Many thanks !!!!!!!

Roland Schulz Contributing Member • Posts: 716
Re: What about dual gain
1

JimKasson wrote:

There is no second stage.

That's already been pointed out.

https://www.dpreview.com/forums/post/61385233

Single stage/parallel cap dual iso was yesterday.

Maybe this also helps:
http://image-sensors-world.blogspot.com/2012/07/omnivision-dual-conversion-gain-and-fd.html

 Roland Schulz's gear list:Roland Schulz's gear list
Nikon D3 Sony a6500
JimKasson
JimKasson Forum Pro • Posts: 28,999
Re: What about dual gain
1

Roland Schulz wrote:

JimKasson wrote:

There is no second stage.

That's already been pointed out.

https://www.dpreview.com/forums/post/61385233

Single stage/parallel cap dual iso was yesterday.

Maybe this also helps:
http://image-sensors-world.blogspot.com/2012/07/omnivision-dual-conversion-gain-and-fd.html

Are you saying that the a7xIII cameras use that circuit arrangement? That would be at variance with what I have thought for years. If so, how do you know that? If not, how is that relevant to the present conversation?

Jim

-- hide signature --
 JimKasson's gear list:JimKasson's gear list
Nikon D5 Sony a7 III Nikon Z7 Fujifilm GFX 100 Sony a7R IV +2 more
Roland Schulz Contributing Member • Posts: 716
Re: What about dual gain
1

I guess none of us here around "really knows" what´s going on on current Sony sensors.

The "dual amp" gain stage is nothing really new these days.
"I" don´t really "know" what´s used on Sony´s sensors, but I hardly think anybody here does. On the other side to me this looks advanced to the former plain switched capacitor design. I guess Sony uses the more advanced technology.

Information:
http://www.andor.com/learning-academy/dual-amplifier-dynamic-range-scmos-dynamic-range

Programmable gain in 2010:
http://image-sensors-world.blogspot.com/2010/11/cmosis-develops-dual-gain-readout-hdr.html

Dual Gain combination to HDR in ARRI Alexa:
https://www.newsshooter.com/2018/02/02/a-look-back-at-the-history-of-the-arri-alexa/

Further, "I" expect the Sony a6500 sensor to be even triple gain. Connecting that camera in videomode to a waveform monitor gives the observer (of the noisefloor) the hint that there are gain steps at ISO500 and ISO2000.
I don´t see the behaviour on the a7M3. There I only see a diffference at ISO640.

For some here it´s interesting to understand technology - so for these it´s relevant.

 Roland Schulz's gear list:Roland Schulz's gear list
Nikon D3 Sony a6500
slstr Senior Member • Posts: 1,031
Re: What about dual gain
1

Roland Schulz wrote:

I guess none of us here around "really knows" what´s going on on current Sony sensors.

The "dual amp" gain stage is nothing really new these days.
"I" don´t really "know" what´s used on Sony´s sensors, but I hardly think anybody here does.

Here is one hint at what might be used

https://www.imaging-resource.com/news/2013/03/01/aptina-sony-agree-to-cross-license-patent-portfolios

On the other side to me this looks advanced to the former plain switched capacitor design. I guess Sony uses the more advanced technology.

Information:
http://www.andor.com/learning-academy/dual-amplifier-dynamic-range-scmos-dynamic-range

Programmable gain in 2010:
http://image-sensors-world.blogspot.com/2010/11/cmosis-develops-dual-gain-readout-hdr.html

Dual Gain combination to HDR in ARRI Alexa:
https://www.newsshooter.com/2018/02/02/a-look-back-at-the-history-of-the-arri-alexa/

Interesting links, thanks.

Further, "I" expect the Sony a6500 sensor to be even triple gain. Connecting that camera in videomode to a waveform monitor gives the observer (of the noisefloor) the hint that there are gain steps at ISO500 and ISO2000.

Interesting that you see the hint at ISO 500 for video, considering switching is at ISO 320 for RAW photo output. http://www.photonstophotos.net/Charts/PDR.htm#Sony%20ILCE-6500

We've seen similar for A7S in "picture mode", that switches to hi gain at ISO2000 when using mechanical shutter, and at ISO1600 when using (12-bit precision) fully electronic shutter aka. silent shutter for pictures.

For reference here are Jim's test results https://blog.kasson.com/the-last-word/sony-a7s-read-noise-in-silent-mode-2/

Have you excluded the possibility that the noise floor difference you observe on a6500 at ISO 2000 on video output is caused by in camera post processing (i.e. filtering, noise reduction etc..) ?

Based on RAW output I have not heard reports of anyone noticing a third "gain bump" around ISO 2000 for any a6x00 cameras. http://www.photonstophotos.net/Charts/PDR.htm#Sony%20ILCE-6000,Sony%20ILCE-6300,Sony%20ILCE-6500

I don´t see the behaviour on the a7M3. There I only see a diffference at ISO640.

For some here it´s interesting to understand technology - so for these it´s relevant.

 slstr's gear list:slstr's gear list
Sony a7S Sony a7 II Sony a7R II Sony a9 Sony E 30mm F3.5 Macro +12 more
Keyboard shortcuts:
FForum MMy threads