Why bother with ISO? We don't need to!

[DocFrankenstein]

I was thinking...

ISO settings are not hardware changes, it's program changes.

When shooting in low light:

If one wants good image quality, he would stay with ISO 100 and aperture wide open, select the lowest acceptable shutter speed for his lens and conditions and shoot raw.

Then, one would come home and post process these dark images until they look good. Sure, it would increase the noise, but I imagine it would give better results because of the manual controls.

[RichardtheSane]

I'm not convinced.

I shoot concerts, and I know that if I were to shoot ISO 100 1/125th second F2.8 at a venue where I would normally shoot ISO 1600 then I would come away with useless images.

Go and try it.

but I imagine it would give better results because of the manual controls.
I'm not sure what you mean here

[DocFrankenstein]

I'm not convinced.

I shoot concerts, and I know that if I were to shoot ISO 100 1/125th second F2.8 at a venue where I would normally shoot ISO 1600 then I would come away with useless images.
Do you do post processing like curves and stuff?

This is purely theoretical BTW
:P

[DocFrankenstein]

Are you saying the whole idea is bogus or are you replying to someone suggesting you buy a Zenitar lens? :?

[RichardtheSane]

I do post processing, with concert shots to get the best out of them I have to.

I adjust the exposure compensation in capture one, and can adjust the curves there. I can then adjust the cures in photoshop.

But if you have either blown the highlights or killed the shadow detail then post processing will do nothing to save it. The sensor has a limitation on what it can capture, I see adjusting the ISO as altering those boundries.

[leony]

Then, one would come home and post process these dark images until they look good. Sure, it would increase the noise, but I imagine it would give better results because of the manual controls.

Your ISO setting determines the shutter/appereture as well as the time the CMOS chip stays active for.

If you shoot the same scene in RAW by doing this:
1) 1/30 sec. @ 5.6 ISO 100
2) 1/30 sec @ 5.6 ISO 1600

Then go home and open both in Photoshop after RAW conversion you will see that there is a reason for ISO settings, even if you shoot RAW.

It is generally true that RAW allows for greater correction after the fact, but that is not to say you can avoid knowing what to do in the first place.

[Scottes]

NOT A CHANCE!

The sensor is more or less split into 5 zones, from light to dark. The right-most, brightest zone capture 2048 levels of details, the next one capture 1024, and so on until the darkest zone which captures a mere 128 levels of detail.

So if you shoot ISO 100 when you should have shot ISO 400 you'd be 2 stops dark, thus not using the two most detailed zones. You'd lose 3/4 of your details. (2048 + 1024 = 3072 out of 4096 levels) .

Read Reichmann's "Expose Right" - http://www.luminous-landscape.com/tutorials/expose-right.shtml

Furthermore, using the RAW converter to add more than 1.5 stops adds too much noise, IMHO.

Here's the difference between something correctly exposed and the same thing pushed 3 stops in Capture 1.

http://www.itsanadventure.com/postimages/3stopcompare.jpg

[DocFrankenstein]

So... higher ISO actually increases the sensitivity of the sensor? Does that mean that a dark object which would have a value of 0 at ISO 100 would have a value of greater than 0 at ISO 800?

[Persian-Rice]

So... higher ISO actually increases the sensitivity of the sensor? Does that mean that a dark object which would have a value of 0 at ISO 100 would have a value of greater than 0 at ISO 800?

Yes and No.
Yes ISO directly effects the sensitivity of the sensor. This is where noise is actually created. Just to elaborate, when people say more photosites on a sensor is not good is because bigger photosites absorb the siginal better, the smaller the photosite the more amplification is needed to create usable data. Hence you need to use a higer ISO to acheive the same level of lighting on a sensor with larger photosites. When you amplify a siginal, you get noise.

As for the second part of the question, The value of the lighting level of the subject does not change, the value is the same. It's just that siginal is amplified until the siginal presents usable data. It's sort of like taking a dark image, and boosting the brightness up or layering it in screen blending mode. Sometimes you get usable data sometimes you just get garble, which is what we call noise.

Cheers.

[hmhm]

It's a semi-common fallacy that ISO is implemented in post-processing, that it's the equivalent of a "levels" adjustment.

ISO is typically described as an "amplifier boost" of the analog signal before A/D conversion. Sometimes, though, you'll hear of the highest ISO levels being just a digital post-processing boost of the prior levels. For instance, I think I've heard that ISO 3200 on the 10D is just done in firmware, I dunno about 1600, but I'm pretty sure that 800 and below are "analog".

Of course, you'd think that there'd be some documentation from Canon that describes this stuff, but it seems that once you get past that teensy "how to push the buttons" instruction manual, you're just left with little crumbs of insight here and there from the forums (e.g. Chuck Westfall). I'd really like to see something like "EF Lens Work" for the "digital stuff".
-harry

[Guillermo Freige]

AFAIK, hmhm is right. The sensor can have a base ISO 100 sensitivity, but you can increase it increasing the dB of gain of the signal amplifier in the analog stage. Of course this increases noise, but at least you are using the whole 12bit of data to represent it. If you shoot in RAW at ISO 100 and the apply exp. compensation (and you can apply +2 or +2.5 depending the program, which allows you to reach ISO 400-640 only) you will be using only a small part of it, and the worse one, as the info is stored in a linear gamma.

[Andy_T]

So... higher ISO actually increases the sensitivity of the sensor? Does that mean that a dark object which would have a value of 0 at ISO 100 would have a value of greater than 0 at ISO 800?

Why don't you try it out yourself as Leony suggested, if you don't believe us obviously? :wink:

ISO is one of the very few things you can not correct in post processing.

Best regards,
Andy

[drisley]

If I shoot a properly exposed ISO1600 shot, it has VERY low noise on the Rebel.
If I shoot an underexposed ISO800 shot, and then try to compensate with C1 Pro after, the results can be pretty aweful and noisy.

[defordphoto]

One of the biggest misconceptions is that a RAW capture captures everything. It does not. If your shot is overblown there is no amount of post-processing that can magically return the detail that the sensor never saw. If your shot is too dark and details are buried in the black, again there is no amount of post-processing that can recover that detail (again) that the sensor never saw.

Digital gives us many, many advantages over film, but it does not compensate for a bad photographer. You still must take the time to set the exposures correctly just like you did with film. If you don't, you'll pay the price with a compromised photo.

Whether RAW or JPEG, a photo that has been "fixed" due to bad photography will always be a "fixed" photo. And a well shot JPEG will beat a poorly shot RAW photo any day of the week.

[robertwgross]

ISO settings are not hardware changes, it's program changes.


I read your theory, and I can't agree very much.

You must set some kind of baseline sensitivity on the sensor.

---Bob Gross---

[ohenry]

GIGO .... garbage in, garbage out!

[Rayz]

All digital cameras have noise reductions systems. Some are better than others. Noise at 100 ISO on the 10D is about the same as that on the D60. But noise at ISO 400 and 800 is less and apparently noise on the 20D is less again.

I still use a D60. Some time ago I tested this issue that Docfrankenstein has raised. Took a correctly exposed shot at ISO 800 and then using the same aperture and shutter speed took progressively more underexposed shots at each lower ISO setting. I then used exposure compensation in BreezeBrowser's RAW converter and compared the 16bit tiffs.

I was surprised at how small the improvement was between an underexposed shot at ISO 100, after EC, and a correctly exposed shot at ISO 800. Nevertheless, the lower noise in the ISO 800 shot was definitely noticeable.

However, comparing a correctly exposed ISO 400 shot with an underexposed ISO 100 shot was even more surprising. The difference in noise levels was not significant at all and I wouldn't be surprised if Adobe's RAW converter would narrow the gap even more.

But that's the D60. Old technology :D .

[abel]

i also shoot concerts and i love the ability to bump up the iso in order to get a faster shuter speed.

concert photography would be out of the question if i did not have that function...

http://www.nitrocross.com/temp\dmbbig.jpg

[Rayz]

i also shoot concerts and i love the ability to bump up the iso in order to get a faster shuter speed.

concert photography would be out of the question if i did not have that function...



With all due respect, Abel, the topic is about the differences between using 'exposure compensation' on an underexposed RAW image at the time of conversion, as opposed to allowing the camera to do the exposure compensation that follows from bumping up the ISO setting.

The essential point is, whatever ISO you choose, at a given aperture and shutter speed the sensor receives the same amount of light.

You don't mention what camera you use. If you are using a D60 and a state-of-the-art RAW converter such as ACR in PS CS, then it wouldn't make much difference if you used ISO 400 or underexposed at ISO 100.

[CyberDyneSystems]

Well.. as others have said.. this is simply not true.. your theory is based on erroneous assumptions.

One of the true benifits of ISO settings with Digital over film is the ability to essentially change film types to suit the needs of the moment without having to go through what is a rather big hassle of changing film cartridges mid roll.

The change made in the ISO setting is a change in the hardware electronics.. not in software.

[DocFrankenstein]

By no means I am trying to argue or flame here. Just thinking outloud I guess.

The sensor receives the same amount of light in both cases. Let's assume for the sake of simplicity that a photocell on the sensor can have a max charge of 8000 electrons.

If I use ISO 100, then the signal from the sensor is recorded as 12 bit number, with 1111 1111 1111 corresponding to 8000 elecrons or pure white.

If I use ISO 800, the 1111 1111 1111 is corresponding to 1000 electrons or pure white.

Now, let's assume that 8 bits information per channel in the final image is enough quality. If we go from ISO 100 to ISO 3200, that's 5 stops... So we'd end up with 128 levels in 3200...

I see the flaws in my "assumption". And I was not considering the fact that the signal is not written linearly. :?

Thank you for all the replies.

[Rayz]

Well.. as others have said.. this is simply not true.. your theory is based on erroneous assumptions.



I'm not sure it's quite that simple. As pointed out in this thread, by Harry I think, increasing the ISO tells the camera's pre-amplifier to increase the gain of the analogue signal from the sensor prior to digitisation. The pre-amplifier is another source of noise. There is some net benefit, but in older models such as the D60 (and I presume the D30) the benefit of this amplification might not be as great as one imagines.

Of course, it also depends on whether you shoot RAW or jpeg. If you shoot jpeg, there's no question that raising the ISO is of great benefit. I would think also there is no question that the 10D, 300D and 20D produce much less noise in high ISO RAW images than an exposure corrected underexposed RAW image at ISO 100.

But this is not the case with the D60 at ISO 400. And this is useful to know because changing ISO involves the pressing of a few buttons. If you were in manual mode and needed to shoot something in a hurry, in the shade, you could get by very nicely with an underexposed RAW image at ISO 100.

[CyberDyneSystems]

I shoot RAW, and I can tell you there is no way that RAW exposure compensation can give you the four full stops that switching from ISO 100 to 1600 can offer... not even close. :wink:

Also.. as for the older models.. I am sure the technology was not as far along.. this is a given.. so whats your point in bringing this up? Are you thinking that perhaps we were unaware that older digitals do not have the same level of high ISO image quality as the newer models? :?

Of course, I think it is safe to assume that must of us are aware of this. :)

As each new Canon DSLR is released the higher ISO capabilities get better and better.. this is the stimulus for this thread I'm pretty sure. We talk it about it more often.. and get excited by the possibilites and potential.. thus this thread of the Doc's.. ie: whats all the hubbub?,.. bub? :lol:

It is the buzz of the improved tech in the cameras ability to shoot at higher ISO's than previously was acceptable that has motivated the question.

As far as it not being that simple? I think it is.. as you then go on to agree with it's simplicity yourself, by making the statement;

there's no question that raising the ISO is of great benefit. I would think also there is no question that the 10D, 300D and 20D produce much less noise in high ISO RAW images than an exposure corrected underexposed RAW image at ISO 100.

Yep... that's 100% accurate.. add in the 1D, 1D mkII, 1Ds, D1, D1h, D1X D2H, S1, S2, S3, and IMHO D60 (as your own test @ ISO 800 seems to confirm) ... :) and to me it's quite simple indeed! :)

[defordphoto]

If you were in manual mode and needed to shoot something in a hurry, in the shade, you could get by very nicely with an underexposed RAW image at ISO 100.

Somewhat underexposed. Again, shooting RAW is not a substitute for not shooting the proper settings. It will show in your photos. Like with film, you can only push the ISO so far, then things get really ugly. In this aspect, the rules of photography have not changed one iota. To get the best shots, whether shooting RAW, NEF, TIFF, JPEG or whatever, always shoot the proper exposure.

[hmhm]

I was surprised at how small the improvement was between an underexposed shot at ISO 100, after EC, and a correctly exposed shot at ISO 800. Nevertheless, the lower noise in the ISO 800 shot was definitely noticeable.

A comparison would need to consider both noise and also dynamic range. It's really dynamic range that I'd think would be the main victim of underexposing ISO100 vs using higher ISOs properly exposed. You'd want to look at noise levels, but also the level of remaining detail in the shadows, posterization, etc.

I can't say I've done the test, myself.
-harry

[CyberDyneSystems]

I was surprised at how small the improvement was between an underexposed shot at ISO 100, after EC, and a correctly exposed shot at ISO 800. Nevertheless, the lower noise in the ISO 800 shot was definitely noticeable.

A comparison would need to consider both noise and also dynamic range. It's really dynamic range that I'd think would be the main victim of underexposing ISO100 vs using higher ISOs properly exposed. You'd want to look at noise levels, but also the level of remaining detail in the shadows, posterization, etc.

I can't say I've done the test, myself.
-harry

Excellent point,.. and it turns out others have done the testing for you.. and made getting the correct exposure in Digital something of a mantra.

Check these links.. the info offered is in fact completely diametrically opposed to the idea of shooting underexposed for the purpose of RAW EC... and with good reason;

http://www.rogercavanagh.com/helpinfo/28_exposeright.htm
http://www.luminous-landscape.com/tutorials/expose-right.shtml

[Rayz]

I shoot RAW, and I can tell you there is no way that RAW exposure compensation can give you the four full stops that switching from ISO 100 to 1600 can offer... not even close. :wink:



CDS,
I'm sure that's true. However, the D60 doesn't have an ISO 1600 capability, and as far as I'm concerned ISO 800 and 1000 are unacceptably noisy on the D60. I never use them.

I do use ISO 400 a lot. I didn't initially because I'm very sensitive to noise. But when I realised I was sacrificing 'tack sharpness' for lower noise, I decided that wasn't a sensible approach.

It was as a result of a similar discussion to this that I actually did the comparison between ISO 100 and 400 with the same aperture and shutter speed, and was surprised to find little difference in noise levels in the shadows. This snippet of information is clearly mainly of interest to D60 owners.

Your reference to the 'expose to the right' advice from Luminous Landscape is not diectly relevant to this issue. If the histogram is not pushing the right side of the frame, then the advice is to increase the exposure, not increase the ISO.

Docfrankenstein's point in this thread is I think a valid one, even though his conclusions are wrong, due to the marvels of technology. With film cameras, ISO is related to the sensitivity of the film. With digital cameras the sensitivity of the sensor is fixed. Increasing ISO in digital cameras is more akin to 'push processing'. For those not familiar with this term, it's using a film with, say an ISO 100 rating as though it were an ISO 400 film, and then telling the film processor that the film has been underexposed and to compensate for it in the development process.

Digital cameras use a type of in-camera 'push processing' when you bump up the ISO. Some cameras are better than others at this.

That's my point. No need to get in a huff about this :) .

[CyberDyneSystems]

No huff at all.. :) merely engaging in discussion.. and differing points of view.

Like this one... :wink:

I DO think that the "expose to the right" info is pertinant to the discusion.. the point being that there is more to the measure of an images quality than just noise.

The allternative to bumping ISO as put forth in this discussion is to underexpose and recover the exposure using the RAW conversion and post processing.

The articles and ideas on "exposing to the right" suggest reasons why this technique would be overall detrimental to the final image.

The articles on exposing to the right explain how a CCD/CMOS sensor gets the most color information and dynamic range to offer an image when the histogram is pushed to the right.

By shooting well underexposed,.. as the alternate to bumbing the ISO.. the camera will loose dramatic amounts of color information. The articles linked illustrates how this technique will hurt your overall image quality far beyond just the noise issue... giving yet another reason why shooting underexposed can be detrimental to your images, beyond just noise.

Hey,. I'm not knocking any one's ideas.. I'm just putting forth my own take on the matter. :)

[Rayz]

By shooting well underexposed,.. as the alternate to bumbing the ISO.. the camera will loose dramatic amounts of color information. The articles linked illustrates how this technique will hurt your overall image quality far beyond just the noise issue... giving yet another reason why shooting underexposed can be detrimental to your images, beyond just noise.



After I've used my 20D for a while (it's on order) I'll probably be in complete agreement with you on this issue :) . For me as a D60 owner it'll be a big improvement. I really look forward to being able to use ISO 800 and 1600 without worrying about noise.

The image degradation as a result of underexposure at ISO 100 on the D60 is not as great as you think, provided one has a bit of skill with Photoshop. One of the techniques I use is to create 2 RAW conversions of the image, one with up to +4 stops over exposure compensation and the other left as it is, say 2 stops underexposed (which would result if I hadn't changed to ISO 400). I then blend the two images using a layer mask and adjust the individual levels of the two layers till I get the balance I want. I find this technique (refer to Luminous Landscape tutorial on Digital Blending) restores the tonality and color to the underexposed parts of the image marvelously.

[CyberDyneSystems]

Oh yes.. I use the multiple "raw exposure" trick too.. a definate advantage!

Some times people ask if we need more megapixels.... (of course we do)

But.. maybe they don't need to be used as just three times as many MPs... = three times the resolution.

I'm waiting for a camera with 24 megapixels.. 8 for the darkest colors.. 8 for the mid range,. and 8 for the brights.. and triple our dynamic range!!!!