[PentaxPoke]

We have all heard about "exposing to the right" in order to increase signal to noise on the sensor. I thought I would run a demonstration of how this can be used to reduce high ISO noise without using noise reduction software, and without reducing detail.

Here is the setup:

k20d, ISO 6400
3 exposures: EV-1, EV0, EV+1
No NR of any type
Shot in RAW, converted to jpeg on "Natural" and "Highest Quality" (be careful of download size)

The EV-1 was "pushed" +1 to get to EV0. The EV+1 shot was "pulled" down to EV0. Compare all the shots. You will see that the noise in the EV+1 "pulled" is significantly lower than the other two. You could make the case to just set the camera to ISO 3200, but I am just trying to illustrate the improved signal to noise of exposing to the right using 1EV steps (because it is convenient)
Expose Right to reduce ISO noise test - a set on Flickr

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Last edited by PentaxPoke; 05-13-2008 at 12:24 AM.

[BBear]

indeed good results...

can you clarfy what/how the "pushes" work?

[PentaxPoke]

Sure. I used steps of 1EV because it was convenient. I simply did a 3-shot 1EV exposure bracket. Then I opened the Pentax Photo Lab. I turned off all noise reduction and set the white balance to "tungsten". On the EV0 shot I simply converted to jpeg. On the EV-1 shot I slid the "sensitivity" slider to the right 1EV, then converted to jpeg. On the EV+1 shot I slid the slider by -1EV and converted. The sensitivity slider changes the effective exposure of the shot.

As I mentioned, you wouldn't do what I did to reduce noise in a general sense. In other words you wouldn't necessarily bump up the EV by 1 on the camera and then pull it back down again in PP. In that case you would be better off just dropping ISO in the camera by 1 stop. The point of the test is that underexposure is bad for noise. "Exposing to the right" is a good guideline to reduce noise at any ISO. As you can see in the "worst" case, it is better to overexpose and correct downward than underexpose and correct the other way. The only "catch" is that you don't want to go so far right that you clip off the desireable highlights. That is easy to check though if you set your LCD to display the histogram as well as the "blinkies."

[bymy141]

We have all heard about "exposing to the right" in order to increase signal to noise on the sensor. I thought I would run a demonstration of how this can be used to reduce high ISO noise without using noise reduction software, and without reducing detail.

Here is the setup:

k20d, ISO 6400
3 exposures: EV-1, EV0, EV+1
No NR of any type
Shot in RAW, converted to jpeg on "Natural" and "Highest Quality" (be careful of download size)

The EV-1 was "pushed" +1 to get to EV0. The EV+1 shot was "pulled" down to EV0. Compare all the shots. You will see that the noise in the EV+1 "pulled" is significantly lower than the other two. You could make the case to just set the camera to ISO 3200, but I am just trying to illustrate the improved signal to noise of exposing to the right using 1EV steps (because it is convenient)
Expose Right to reduce ISO noise test - a set on Flickr

We have had this discussion before and I still believe you are fooling yourself, assuming that you what to shoot with ISO 3200 to have a faster shutter speed.

It is true that dark areas show much more noise than light areas.
The signal there is lower, therefore the signal to noise ratio is worse.

However.... let me try and explain.

There are only 3 parameters to influence your exposure:
1. Lens opening / aperture
2. Shutter speed
3. ISO value (more or less amplifying the sensor signal)

The EV value is influencing the metering mechanism of your camera.

So, what it does at EV -1 and ISO 3200 and a maximum lens opening (I assume) is; it will half your shutter speed.
Was having a faster shutter speed not the reason to shoot at ISO 3200 in the first place? Now, you have just undone that.

You might as well remain at the same shutter speed (half that is) and aperture, with no EV change a lower the ISO value to 1600 for lower noise.
You will have less noise as well and you will have 1 stop more dynamic range to work with!

- Bert

[pentagor]

I absolutely agree with Bert! You have three parameters, which define the exposure. With aperture you control the DOF, the shutter speed is chosen on behalf of you subject speed etc. and ISO is the last parameter, which is preferred to stay as low as possible, because of noise it produces (well the ISO doesn't produce noise, but you know what I mean).
So what you have done at ISO 6400 with EV 1+, you could do at ISO 3200 and EV 0.

[PentaxPoke]

So what you have done at ISO 6400 with EV 1+, you could do at ISO 3200 and EV 0.

I understand that. Did you read my posts? That is why I made that exact point above (twice). I also understand exposure. For the third time: I chose that ISO and that EV number because it was convenient and easy to demonstrate the effect of exposure on noise at a given ISO.

My point was simply that underexposure is bad for noise. Not all new DSLR owners are aware of this. At some point the photographer needs to make a decision about the exposure. Unless you just pointed your camera at a grey card, there are still decisions you have to make about what is the proper exposure. My point is simply don't underexpose! If anything, shift to the right.

[jonboy]

And blow out your highlights? No thanks, that's not for me.

[bymy141]

I understand that. Did you read my posts? That is why I made that exact point above (twice). I also understand exposure. For the third time: I chose that ISO and that EV number because it was convenient and easy to demonstrate the effect of exposure on noise at a given ISO.

My point was simply that underexposure is bad for noise. Not all new DSLR owners are aware of this. At some point the photographer needs to make a decision about the exposure. Unless you just pointed your camera at a grey card, there are still decisions you have to make about what is the proper exposure. My point is simply don't underexpose! If anything, shift to the right.

Point taken.
I misinterpreted your post and was under the impression by the demonstration method used that you advised people to overexpose using the EV method in high ISO usage.
The matter that remains to be solved is: right exposure with ISO versus over exposure with ISO x 2. Results may be non linear.
I do not have a K20D, but did try and test this with my K10D.

These are crops from dark parts of 4 pictures taken in my study: 1600 + Ev, 800, 800+1Ev, 400 ISO.
In order to compare the images side by side properly, I lowered the "over exposed" images with 1 EV in Lightroom before exporting.

See here the results for ISO 1600 +1Ev versus ISO 800:

ISO 1600 +1EV in camera, -1EV in Lightroom (nr off)
Attachment 12142
versus ISO 800, no EV compensation (nr off):
Attachment 12145

and for ISO 800 +1Ev versus ISO 400:

ISO 800+1EV in camera, -1EV in Lightroom (nr off)
Attachment 12144
versus ISO 400, no EV compensation (nr off):
Attachment 12147

Looking at the results (magnified), I guess the lower ISO results are the better ones.

- Bert

[PentaxPoke]

And blow out your highlights? No thanks, that's not for me.

Who said blow highlights? Certainly not me! Did I blow the highlights in this example? No. Did you read my post above regarding highlights? Post #3. Seriously, it is basic forum etiquette to actually read a thread before commenting. There is a whole wide range between underexposure and blowing highlights.

Thanks for the pics bymy. Those provide a useful comparison. I think we agree on the following:

1) Lower ISO in the camera is always better.
2) For any given ISO, underexposure leads to noise.

Point 2 is the point I was trying to make. It is old news to people with alot of DSLR experience, but this forum is about helping people, and I wanted to give a simple example to make the point to people new to DSLR's. The pictures we see where people are complaining about noise and asking "what do I do" are usually underexposed. Is'nt it amazing how low the noise is at ISO6400 when not underexposed? There is a wide contrast in the images. From deep black to bright white, and it was still possible to keep the highlights and shadows within the DR of the k20d.

[Film2Digital]

Thanks PxP.
Most times when shooting indoor sports you Need the
highest ISO you can find to get close to the necessary shutter speed.
The K10D's ISO 1600 isn't really enough so you make do.
ISO 800 (as per bymy's example) isn't anywhere high enough.
Hand-held, lower light, fast-moving shots require high ISO settings.

[Outlaw]

Who said blow highlights? Certainly not me! Did I blow the highlights in this example? No. Did you read my post above regarding highlights? Post #3. Seriously, it is basic forum etiquette to actually read a thread before commenting. There is a whole wide range between underexposure and blowing highlights.

Thanks for the pics bymy. Those provide a useful comparison. I think we agree on the following:

1) Lower ISO in the camera is always better.
2) For any given ISO, underexposure leads to noise.

Point 2 is the point I was trying to make. It is old news to people with alot of DSLR experience, but this forum is about helping people, and I wanted to give a simple example to make the point to people new to DSLR's. The pictures we see where people are complaining about noise and asking "what do I do" are usually underexposed. Is'nt it amazing how low the noise is at ISO6400 when not underexposed? There is a wide contrast in the images. From deep black to bright white, and it was still possible to keep the highlights and shadows within the DR of the k20d.

Thanks PentaxPoke (& Bert),

I am still struggling with ISO vs Exposure and trying to "get it right" in lower light situations.

So if I read correctly, what you have posted, if higher ISO is needed, then make sure to increase the exposure to compensate for noise and this will allow a faster shuuter?.

I am sure you made it clear, I just want to be sure I understood you properly.

I guess practice is needed to get the levels right, just gotta find the time

[jbinpg]

I did some shooting in daylight at ISO 3200 the other day. Impressive results after post-processing. One shot can be seen here:

King Rat on Flickr - Photo Sharing!

[PentaxPoke]

Nice job jbinpg. You know, we should start a Pentax Forums Album filled will all the great shots people here are taking with thier Pentax cameras at "unuseable" iso (according to popphoto). What are these reviewers thinking?

Outlaw, there is a tradeoff between the noise and shutter speed. Of course if we want to increase the exposure, we either have to decrease shutter speed or increase aperture. I was really not trying to say anything more profound than this:

underexposure=more noise.

So at any ISO you choose, you will get less noise if you expose to the high end of the dynamic range of your camera instead of the low end. Some argue that the best way to choose exposure for a DSLR (as opposed to film) is to expose just to the point before clipping the highlights. In other words, to the right. This is easy to do by turning on the "blinking" in the lcd preview. The common reference on this is here:
Expose Right

Everything is a tradeoff, but the bottom line is that
exposing right=less noise
exposing left=more noise but faster shutter or larger DOF

[Outlaw]

Nice job jbinpg. You know, we should start a Pentax Forums Album filled will all the great shots people here are taking with thier Pentax cameras at "unuseable" iso (according to popphoto). What are these reviewers thinking?

Outlaw, there is a tradeoff between the noise and shutter speed. Of course if we want to increase the exposure, we either have to decrease shutter speed or increase aperture. I was really not trying to say anything more profound than this:

underexposure=more noise.

So at any ISO you choose, you will get less noise if you expose to the high end of the dynamic range of your camera instead of the low end. Some argue that the best way to choose exposure for a DSLR (as opposed to film) is to expose just to the point before clipping the highlights. In other words, to the right. This is easy to do by turning on the "blinking" in the lcd preview. The common reference on this is here:
Expose Right

Everything is a tradeoff, but the bottom line is that
exposing right=less noise
exposing left=more noise but faster shutter or larger DOF

Thanks for that, I appreciate the clarification. Will try this on the weekend - I have the feeling a new world will open up

[PentaxPoke]

Thanks Outlaw. Good luck, and post some of your tests for us to see!