Noise reduction by INCREASING ISO

FM Forum Rules
Canon SLRs, primes, and zooms lenses reviews

FM Forums \| Canon-mount SLRs \| Join Upload & Sell	Search Used
1 2 end

Archive 2004 · Noise reduction by INCREASING ISO

gfiksel
Offline
Upload & Sell: On

p.2 #1 · Noise reduction by INCREASING ISO

sfowler wrote:
I agree with Mike B. this is the concept of exposing right. There are several articles about this topic and a very good one can be found on Roger Cavanagh's website. There is also an interview I read with the developers of Adobe Camera Raw who explain why this works. It is because half of the entire dynamic range information of a photograph comes from the right 1/5 of the historgram. Therefore, if you expose right as far as you can without blowing the highlights and then adjust EC in development you will increase dynamic range and decrease noise. I highly recommend looking up articles on this topic.

Stephen
Stephen,

I totally agree with what you are saying and I am very well familiar with those articles.

I am afraid of sounding like a broken record but frequently you just can't increase the available litght level. What is interesting in the given case that the concept works even when you are exposing more to the right by increasing the ISO, which is usually associated with the noise growth.

Feb 29, 2004 at 09:09 PM

MikeBinOKlahom
Offline
Upload & Sell: Off

p.2 #2 · Noise reduction by INCREASING ISO

Here is a link to the Roger Cavanagh article Stephen mentioned:

http://www.rogercavanagh.com/helpinfo/28_exposeright.htm

The comments that said this could result in blown highlights are correct--So you can't use this technique in a photo which is pushing the right side of the histogram already.

This technique DOES effectively amount to increasing exposure time that you'd normally use for the ISO in question. So it may not be appropriate for action shots.

I don't have a 1-series camera yet (waiting patiently on my 1Ds from Adorama--Sigh), but seems like the audio file feature on the high-end cameras would be a good place for verbal note-taking on what you've done, including how much overexposure. Ideally, I'd be such a skilled photographer that I'd be able to deduce this from studying the RAW the image, and often I can, but I'd rather KNOW. :-)

Feb 29, 2004 at 09:12 PM

enrico
Offline
Upload & Sell: Off

p.2 #3 · Noise reduction by INCREASING ISO

Just a thought:
I think that there is always some sort of noise reduction in camera (it's the manufacturer know-how) and probably with higher ISO it is more aggressive, probably at the expence of something else (details likely). That could explain why the strange procedure seems to work (otherwise the S/N ratio should be invariated, since overexposing one stop and at the same time doubling the ISO setting would mean that the same amount of light reach the sensor).

Feb 29, 2004 at 10:53 PM

Nate Fabro
Offline
Upload & Sell: Off

p.2 #4 · Noise reduction by INCREASING ISO

This is merley a consequence of "exposing to the right." While it works to control noise, in the real world I would hope we are taking pictures of things with a bit more dynamic range than a grey card. When you have a lot of dynamic range in the picture, you probably will not be able to do this without blowing the highlights.

Mar 01, 2004 at 01:49 AM

Jeff
Offline
Dedicated FM
Upload & Sell: On

p.2 #5 · Noise reduction by INCREASING ISO

Interesting. I'd like to see as one of your grey card examples a shot at 800 ISO, overexposed by one stop, then brought back. Also, maybe doing such a test on a color swatch card (with grey scale) might be more informative as to actual real-world results (as far as exposure issues with highlights go).

Mar 01, 2004 at 06:53 AM

coolmib
Offline
Upload & Sell: Off

p.2 #6 · Noise reduction by INCREASING ISO

I'm wondering if this phoenomenon applies to D60. Any one tried?

Also, for the grey card, the histogram is in the dead center, a +1 over exposure won't push the curve off chart. But in real life, a +1 over could wash out the high light ...

Mar 01, 2004 at 08:24 AM

Kyle Yates
Offline
Dedicated FM
Upload & Sell: Off

p.2 #7 · Noise reduction by INCREASING ISO

This sort of technique has been used in the "Traditional Wet Darkroom" for years and was known as "Pushing / Pulling".

You would either deliberately over / under expose the original film shot on the camera and then in the development process you would then increase / decrease the developement time. You could do this either when the film itself was being developed -- not usually good unless the whole roll was under / over exposed, or at printing time which gave you the maximum flexibility. Of course you didn't have Photoshop Layers then.

The principles ares similar for digital -- but if you want good analysis read some of the older photographic texts on "Pushing / Pulling". It's still valid for digital as "Noise" is equivalent to Grain.

Yes it DOES work in a D60 or any other camera where you can either manually set the exposure / aperture or dial in exposure compensation.

Mar 01, 2004 at 09:48 AM

gfiksel
Offline
Upload & Sell: On

p.2 #8 · Noise reduction by INCREASING ISO

Even in a real life pushing +1 still leaves enough padding on the right due to a large dynamic range of the sensor.
As far as other cameras, I guess, it depends on the noise vs. ISO curve. But, it's digital, costs nothing to try

Mar 01, 2004 at 12:58 PM

gfiksel
Offline
Upload & Sell: On

p.2 #9 · Noise reduction by INCREASING ISO

Thanks, Kyle. Very interesting notion.

Mar 01, 2004 at 12:58 PM

David Savkovic
Offline
Upload & Sell: Off

p.2 #10 · Noise reduction by INCREASING ISO

I like this info. I am going to try it with my D100 and 1D.

Mar 02, 2004 at 10:19 PM

Peter
Offline
Upload & Sell: Off

p.2 #11 · Noise reduction by INCREASING ISO

Hi Guys- I think I can lay claim to first describing this technique. I discovered it using the kodak 720X which has a very large DR with up to 2 stops recoverable "blown" highlights. I also noticed that ISO noise did not increase as fast as Iso steps, and for very high Iso shooting with this incredibly clean sensor, like 2400 and up, I demonstrated that you get cleaner files "pushing" the exposure by up to 1 stop, and "pulling" the exposure back in the Raw converter, than by fully exposing without overexposing at the 1 stop lower ISO. I coined "push-pull" for this and you'll see it in Golbraith's Kodak forum going back well before even Reichman wrote about it. It also works with the 14N, and should with any DSLR as long as the DR is there to recover the details. I liken this to Dolby tape hiss reduction where in order to increase the S/N ration, you add noise and saturate the dynamic range then remove the Dolby noise in the playback. Anyway, it's worth trying, and nobody is getting rich on it, so what the heck. Best....Peter

Mar 02, 2004 at 11:00 PM

1 2 end
FM Forums \| Canon-mount SLRs \| Join Upload & Sell 1 2 end