Why video use "GAIN" instead "ISO" ?

Started Mar 13, 2009 | Discussions
Silverback1988 Contributing Member • Posts: 706
Why video use "GAIN" instead "ISO" ?

For sensor sensitivity, still camera using "ISO", like ISO 100, 200, etc
But camcoders using "GAIN" like 0 db, +6 db, etc

Is it just different name like, centimeter & inch, or else ?
What is the difference between those two ?

Thanks

ccs_hello Regular Member • Posts: 273
Re: Why video use "GAIN" instead "ISO" ?

"ISO" number is the calibrated "Gain". Skip that step is easy to do.

IMHO, the real reason is the camcorders are using much smaller sensor area (e.g., type-1/6" sensor), and very often, not all the sensor area are used for output. Use the standardized value will simply show: which model is poorer.

ccs_hello

Photato
Photato Senior Member • Posts: 2,845
Because of Live View.....

Nowadays Digital Cameras can as well use Gain but unfortunately they came with the baggage of legacy film and a market hostile to anything different.

In the film days you were shooting blind so the whole Camera Film System evolved around Exposure calculations. ISO, Flash Guide numbers, Light Meters, exposures tips and rules etc, etc
Video never had that that problem since they can see 'exposure' in real time.

So with FILM, ISO is/was absolutely necessary to calculate correct EXPOSURE around the system.

Now that we have instant preview there are few reasons to use ISO in modern digital.
Sure it still a bit useful in some rare cases but I can live without it.

I think is way overdue for manufacturers to start offering Gain as well as ISO and let the user decide what works best for them.

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OP Silverback1988 Contributing Member • Posts: 706
Re: Why video use "GAIN" instead "ISO" ?

ccs_hello wrote:

.... Use the standardized value will simply
show: which model is poorer.

ccs_hello
--

Do you mean 0 (zero) db in camera A IS NOT THE SAME sensitivity as camera B ?
As I know ISO 100 in DSLR A is the same sensitivity as ISO 100 in DSLR B.

Thanks for the reply.

Ajaya Contributing Member • Posts: 580
I think the Gain worked more like the Auto ISO

I remember way back I had a Hitachi 3 chip Hi 8 Video camera and I would leave it at +9 gain and under most condition the gain would not kick-in until the scene got dark. The newer digital photo cameras on auto ISO behave the same way. So I feel gain of +6 might mean auto ISO 100-400 and gain +9 may mean auto ISO 100-800. Correct me if I am wrong, I think they tried to keep it simple and got the job done!
Ajay
http://www.PreciousVideoMemories.Com

Photato
Photato Senior Member • Posts: 2,845
Re: Why video use "GAIN" instead "ISO" ?

Silverback1988 wrote:

ccs_hello wrote:

.... Use the standardized value will simply
show: which model is poorer.

ccs_hello
--

Do you mean 0 (zero) db in camera A IS NOT THE SAME sensitivity as
camera B ?
As I know ISO 100 in DSLR A is the same sensitivity as ISO 100 in
DSLR B.

That is not true. On paper ISO100 should be the same on any camera, unfortunately in practice is different.

More important however is the accuracy of the reported aperture and accumulation time. Manufactures can cheat either in ISO, Aperture or accumulation time to push the low light performance.
Most reviewers don't go as far as to check for the accuracy of those.

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Wayne Larmon Forum Pro • Posts: 10,687
The reasons for ISO rating are becoming anachronistic

Photato wrote:

Nowadays Digital Cameras can as well use Gain but unfortunately they
came with the baggage of legacy film and a market hostile to anything
different.

In the film days you were shooting blind so the whole Camera Film
System evolved around Exposure calculations. ISO, Flash Guide
numbers, Light Meters, exposures tips and rules etc, etc
Video never had that that problem since they can see 'exposure' in
real time.

So with FILM, ISO is/was absolutely necessary to calculate correct
EXPOSURE around the system.

Now that we have instant preview there are few reasons to use ISO in
modern digital.
Sure it still a bit useful in some rare cases but I can live without it.

I think is way overdue for manufacturers to start offering Gain as
well as ISO and let the user decide what works best for them.

Agree. The concept of ISO ratings were needed when photographers shoot blind. For film photographers, this was always the case. For DSLR photographers, this is sometimes the case (for the cases when there isn't time to chimp the histogram before you dial in exposure compensation for the shot that counts).

But for the cases where the camera has a live histogram (preferably, in the viewfinder), the case is that you are never shooting blind. If you have a live histogram, then the most logical control would be a gain knob that you'd dial in while watching the histogram. Because a live histogram in the viewfinder pretty much assumes an EVIL camera, you'd also be judging what portions of the image are blowing out (if the scene had a high dynamic range and you needed to trade off blown highlights for shadow detail, and wanted to see how much blown highlights you can live with.)

My Canon G9 has a live histogram (on the back LCD) and a dedicated ISO dial on the top of the camera. So I can come close to this ideal if I'm shooting in manual mode (and sunlight isn't obscuring the LCD.) I can set the aperture and shutter speed that I want and then turn the ISO wheel until the histogram is what I want. From there, it would only be a small step to turn the ISO wheel into a gain trim control wheel.

But this probably won't happen until EVIL camera are more prevalent and seeing live histograms in the EVF is more common. Right now, DSLRs are the cameras that serious photographers use and no DSLR has a live histogram in the viewfinder. So "dialing in the exposure while watching the histogram" is impossible. (Yes, you can use the meter, but this only works if you use spot metering and have the spot pointed to the portion of the image that you know is the brightest. Setting this up requires more mental effort than watching a digital version of the completed image and histogram in real time. Good EVF==what you will eventually see in Light Room or PhotoShop. OVF isn't.)

I did audio before I got into photography and I was used to seeing gain trim controls. Knowing that digital cameras are entirely electronic and that digital "ISO" was really an analog gain adjustment, it grates me so have to mentally translate "gain" into "ISO." (But I can understand why photographers that started with film are more comfortable with ISO ratings. For the same reason--you want to think in the same terms you always thought of.)

This could be thought of as a good (meaning the comfortable, same old ways) versus EVIL argument. If EVIL cameras become popular, they will be disruptive in many ways (possibly needing to throw all your existing lenses away and start over, from scratch...), so I can see why the "EVIL" designation snapped into place on DPReview--because those that understand can foresee the disruptions. "May you be born in interesting times."

Wayne

Vladyslav Kosulin Senior Member • Posts: 2,362
Re: I think the Gain worked more like the Auto ISO

Most camcorders allow to lock the gain to specific value.
--
Vlad

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JoeVC Contributing Member • Posts: 703
Re: I think the Gain worked more like the Auto ISO

The term "ISO" refers to specific standards for measuring photographic film speed as determined by the International Standards Organization. Prior to ISO the term "ASA" was used in the US, and "DIN" was used in many other parts of the world.

Video formats predate the ISO organization (for instance, the NTSC - National Television Systems Committee - standard of the late 1940s, which is still used in digital cameras to this day, when output as analog composite video), and because they electronically amplify the video signal along a chain of circuitry, it became obvious to use the decibel terminology to express gain, as this was an already established electronics terminology for measuring the gain from one point in a circuit to another.

In short, "ISO" is a photosensitometry terminology, while dB is an electronics terminology.

Joe

OP Silverback1988 Contributing Member • Posts: 706
Re: I think the Gain worked more like the Auto ISO

JoeVC wrote:

In short, "ISO" is a photosensitometry terminology, while dB is an
electronics terminology.

Joe
--

Can we translate them one into another ?
Like 1 inch = 2.5 cm ?

ie. Gain 0 db = ISO 100 ?
or ISO 800 = GAIN +6 db ?

OP Silverback1988 Contributing Member • Posts: 706
Re: Why video use "GAIN" instead "ISO" ?

Photato wrote:

That is not true. On paper ISO100 should be the same on any camera,
unfortunately in practice is different.

I can see that.
Canon EOS 30D's ISO 100 is ISO 125 actually.
But it's rather a defect for certain product, am I correct ?
which I like this kind of defect, not the other around.

More important however is the accuracy of the reported aperture and
accumulation time. Manufactures can cheat either in ISO, Aperture or
accumulation time to push the low light performance.
Most reviewers don't go as far as to check for the accuracy of those.

Yes, Unfortunately.
But as I know, dpreview check for the ISO.

MikeAusA200 Senior Member • Posts: 2,057
Re: Why video use "GAIN" instead "ISO" ?

A digital sensor has a sensitivity to light that cannot be changed.

To produce a digital output that has the same response at less light, the camera amplifies the output from the sensor - this GAIN can be delivered in the analogue or the digital part of the chain.

ISO is still used for this change in gain for historic reasons.

A doubling in ISO means a gain of +6db.

JoeVC Contributing Member • Posts: 703
Re: I think the Gain worked more like the Auto ISO

Silverback1988 wrote:

JoeVC wrote:

In short, "ISO" is a photosensitometry terminology, while dB is an
electronics terminology.

Joe
--

Can we translate them one into another ?
Like 1 inch = 2.5 cm ?

ie. Gain 0 db = ISO 100 ?
or ISO 800 = GAIN +6 db ?

Mike is correct when he stated:
"A doubling in ISO means a gain of +6db. "

However, dB by itself is a unitless terminology. Which is why, in audio signals, a third term was appended onto the phrase, hence "dBv" or "dBm", etc., which implied how many volts was referenced at 0dB.

I don't think there's an easy equivalent to 0dB as an ISO figure when refering to film sensitivity; although I haven't delved into the depths of the ISO standard itself, either.

Joe

ccs_hello Regular Member • Posts: 273
Re: Why video use

Let me try to describe it again:

ISO value is an attempt to standardize the sensitivity figure of merit. It is kind of based on absolute scale.

In real life, the calibration is not absolute and can be fuzzy at times. That's why people noticed that a brand X/model Y's ISO 100 is really ISO125... Close enough is good enough

Also note that high sensitivity does not guarantee the noise will not be low. A brand X/model Y's ISO 1600 can be extremely noisy/unusable than another brand/model's.

dB as the method to express gain is always on a relative scale. Low signal to begin with from the image sensor even with extra high gain does not mean the image system is going to be a high ISO and usable camera/digicam.

ccs_hello

Lacol Senior Member • Posts: 1,298
Why are railroad tracks the width of two horses butts ?

video uses gain and digital photography uses iso for historical reasons, period.

When the first dlsr's appeared, they had two be as similar as possible to their film counterparts, or the very conservative film slr user base would never have adopted them. To make it easier for film users to transpose their photographic experience and knowledge to digital, they had to see concepts they were familiar with, like aperture, shutter speed, and yes, iso.

OP Silverback1988 Contributing Member • Posts: 706
Re: Why video use "GAIN" instead "ISO" ?

MikeAusA200 wrote:

A digital sensor has a sensitivity to light that cannot be changed.

To produce a digital output that has the same response at less light,
the camera amplifies the output from the sensor - this GAIN can be
delivered in the analogue or the digital part of the chain.

ISO is still used for this change in gain for historic reasons.

So, the DSLR's ISO is actually GAIN that translated into ISO ?

A doubling in ISO means a gain of +6db.

Yes.
I have camcorders with 2 different brands.
Brand A is 1 stop more sensitive than Brand B at 0 db, and so on,
at +6 db : Brand A still 1 stop apart from Brand B.
1 stop is huge enough.

Is there any standard for gain 0 ?
ie. Gain 0 is ISO 400 ?

Thanks for the answer Mike.

OP Silverback1988 Contributing Member • Posts: 706
I have already measured my camcorders' GAIN

JoeVC wrote:

Mike is correct when he stated:
"A doubling in ISO means a gain of +6db. "

Yes.

However, dB by itself is a unitless terminology. Which is why, in
audio signals, a third term was appended onto the phrase, hence "dBv"
or "dBm", etc., which implied how many volts was referenced at 0dB.

I don't think there's an easy equivalent to 0dB as an ISO figure when
refering to film sensitivity; although I haven't delved into the
depths of the ISO standard itself, either.

I have 5 camcorders with 2 different brands, and I have measured them,
Brand A's gain 0 db is ISO 400, ---> gain +6 db = ISO 800
Brand B's gain 0 db is ISO 200, ---> gain +6 db = ISO 400
the level of noise is just the same at same db.

Brand A's previous model has the same sensitivity as Brand A camcorder, gain 0 db is ISO 400.

When the light is dim, the Brand B give up first.

Unlike ISO, GAIN is rather confusing the user.
They will think gain +6 db is the same sensitivity, no matter brand or model.

And yes, like the other poster has said,
it will hide the inferior model from the other models.

Joe
--

Charlie Self Veteran Member • Posts: 3,924
Re: I have already measured my camcorders' GAIN

Silverback1988 wrote:

JoeVC wrote:

Mike is correct when he stated:
"A doubling in ISO means a gain of +6db. "

Yes.

However, dB by itself is a unitless terminology. Which is why, in
audio signals, a third term was appended onto the phrase, hence "dBv"
or "dBm", etc., which implied how many volts was referenced at 0dB.

I don't think there's an easy equivalent to 0dB as an ISO figure when
refering to film sensitivity; although I haven't delved into the
depths of the ISO standard itself, either.

I have 5 camcorders with 2 different brands, and I have measured them,
Brand A's gain 0 db is ISO 400, ---> gain +6 db = ISO 800
Brand B's gain 0 db is ISO 200, ---> gain +6 db = ISO 400
the level of noise is just the same at same db.

Brand A's previous model has the same sensitivity as Brand A
camcorder, gain 0 db is ISO 400.

When the light is dim, the Brand B give up first.

Unlike ISO, GAIN is rather confusing the user.
They will think gain +6 db is the same sensitivity, no matter brand
or model.

And yes, like the other poster has said,
it will hide the inferior model from the other models.

Your last two comments answer your original question: there's no only no reason to replace ISO with gain, but every reason to remain with ISO. It is not confusing, ISO 100 means the same from brand to brand (allowing for sample variations from brand-to-brand), and ISO doesn't become a shadow hiding the good/bad quality of the camera.

-- hide signature --
Wayne Larmon Forum Pro • Posts: 10,687
Re: Why are railroad tracks the width of two horses butts ?

Lacol wrote:

video uses gain and digital photography uses iso for historical
reasons, period.

When the first dlsr's appeared, they had two be as similar as
possible to their film counterparts, or the very conservative film
slr user base would never have adopted them. To make it easier for
film users to transpose their photographic experience and knowledge
to digital, they had to see concepts they were familiar with, like
aperture, shutter speed, and yes, iso.

I agree with you, but I think that by now most photographers have made the switch to digital and now know the difference. Film cameras had two parameters that need fine adjustment for every shot (unless you are shooting in a studio (or on a tripod) with controlled lighting): shutter speed and aperture. Digital cameras have three: shutter speed, aperture, and ISO (or gain). It is high time for manufacturers to put dedicated ISO dials on the exterior of camera bodies (like I already have on my Canon G9.)

EVIL cameras will add white balance to the mix (becasue you will be able to see if the camera's white balance differs from the actual scene in the EVF), so EVIL cameras should also have dedicated WB controls. (Yes, you can adjust WB on RAW files in PP, but if you can nail WB (along with exposure) in the field, this removes some of the rationale from needing to always shoot RAW.)

You can't move forward while clinging to the past.

Wayne

harrygilbert Senior Member • Posts: 2,799
Re: Why video use "GAIN" instead "ISO" ?

Because ISO (previously ASA in America) was an objective measurement of FILM, while in electronics, gain is a measure of the ability of a circuit (often an amplifier) to increase the power or amplitude of a signal

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