Question #2: exposure compensation vs ISO

What's the difference between the two? As far as I know, increasing ISO would produce noise while increasing exposure compensation doens't. Is that the only difference? If so then adjusting ISO would be useless then?

Your help is much appreciated

Stardust

Stardust said:

What's the difference between the two? As far as I know,
increasing ISO would produce noise while increasing exposure
compensation doens't. Is that the only difference? If so then
adjusting ISO would be useless then?

Your help is much appreciated

Stardust

Click to expand...

Page 68 ... If I understand the manual correctly, exposure
compensation is making fine adjustments to apeture and/or
shutter speeds; however, the viewfinder may not be
reflecting any changes to aperture and/or shutter speeds,
when in fact changes may have occurred.

Page 65 ... ISO is terminology carried-over to digital cameras
from film cameras. Read page 65.

This web site also has a glossary, which applies to most digital
cameras:

http://www.dpreview.com/learn/glossary/

William

You would increase the ISO to help get a faster shutter speed if you need it. For example, shooting a moving object in a dim room without flash is a situation where you might have to increase the ISO to get a fast enough shutter speed to hand hold the camera without blurring. Increasing the exposure simply shifts the dynamic range of the photo toward the lighter end of the spectrum to allow you to hold details there (you will then lose details in the shadows). So if you had a brown cat moving in a dim room and you didn't want to use flash, simply increasing the exposure would give you a lighter blurry cat. Increasing the ISO might give you a clearer cat, along with some noise in the dark parts of the photo. This is my understanding at least, so hopefully someone will correct me if I'm wrong. I don't have a lot of experience with shooting in the dark.

Stardust said:

What's the difference between the two? As far as I know,
increasing ISO would produce noise while increasing exposure
compensation doens't. Is that the only difference? If so then
adjusting ISO would be useless then?

Your help is much appreciated

Stardust

Click to expand...

--
Ty Cooper

Increasing the ISO setting increases the sensitivity of the CCD (in a matter of speaking, anyway), and also increases the amount of noise in the resulting image. This is similar to getting increased grain with higher-ISO film.

Changing the ISO will allow you to use smaller apertures (larger f/numbers) or faster shutter speeds for the same exposure, with higher noise as the penalty.

Exposure compensation allows you to deliberately over- or underexpose the image relative to the exposure recommended by the camera metering.

Using exposure compensation will result in a lighter or darker image, which probably isn't what you have in mind.

--Larry

Stardust said:

What's the difference between the two? As far as I know,
increasing ISO would produce noise while increasing exposure
compensation doens't. Is that the only difference? If so then
adjusting ISO would be useless then?

Your help is much appreciated

Stardust

Click to expand...

Because Dimage F100 doesn't come with noise reduction, I tend to increase exposure compensation instead of increasing ISO (as I don't like to spend time editing photos to reduce noise after taking pictures). I guess there's nothing I can do about it?

Stardust

Stardust said:

What's the difference between the two? As far as I know,
increasing ISO would produce noise while increasing exposure
compensation doens't. Is that the only difference? If so then
adjusting ISO would be useless then?

Your help is much appreciated

Stardust

Click to expand...

Stardust said:

Stardust

Stardust said:

What's the difference between the two? As far as I know,
increasing ISO would produce noise while increasing exposure
compensation doens't. Is that the only difference? If so then
adjusting ISO would be useless then?

Your help is much appreciated

Stardust

Click to expand...

Click to expand...

--

This subject was discussed on Byan Bigger's forum, http://www.network54.com/Hide/Forum/151930 , in early to late September. You may want to look it up there.

In my own, very brief, testing I found that, for shooting in JPEG, I could under expose by two stops (instead of using iso 400) and in post processing increase the exposure. I did not appear to lose much of anything in the dark areas and there was significantly less noise. The JPEG file size for the iso 400 photo was 50% larger than the JPEG file for the iso 100 photo. I had a blank wall as part of the photo. For iso 100, jpeg really compressed this, but at iso 400 the noise prevented the large compression.

Starting then, I lower the exposure compensation first, and then if I still need a faster shutter speed, I increase the iso setting.

Bob Sheldon

Larry,

As usual, your responses are the most accurate and to the point. I would describe ISO settings on a digital camera another way: you are actually turning up the gain on the CCD. That's what causes the noise. Using exposure compensation changes the aperture or sutter speed in such a way as to cause more (or less) light to reach the CCD. That is completely different than increasing the gain. What happens when you are trying to hand hold a shot and the aperture is open all the way and shutter speed is down to 1/30 second? You must increase the ISO in order to take the photo, unless it's a stationary subject and you have a tripod.

An analogy which might help folks understand the difference is this: Suppose are listening to a stereo sytem and have a hearing aid. If the sound is too weak to hear, you have the choice of cranking up the volume on the stereo or turning up the gain on your hearing aid. Increasing the stereo volume would solve the problem if the system has enough power. This is like exposure compensation. On a good system, there will be no increase in noise but you might not have enough amplification to do it. If instead you turn up the hearing aid gain, it's like increasing the ISO (more sensitivity at your ears (CCD)). But any room noise will also be amplified which could ruin your listening experience. I know that CCD noise is not the same as room noise, but the results are the same.

Does this help those who are still confused or is it simply pouring salt in the wound.

Dewdrop

Larry Cunningham said:

Exposure compensation allows you to deliberately over- or
underexpose the image relative to the exposure recommended by the
camera metering.
Using exposure compensation will result in a lighter or darker
image, which probably isn't what you have in mind.

--Larry

Stardust said:

What's the difference between the two? As far as I know,
increasing ISO would produce noise while increasing exposure
compensation doens't. Is that the only difference? If so then
adjusting ISO would be useless then?

Your help is much appreciated

Stardust

Click to expand...

Click to expand...

The strategy you've described is pretty much the same approach I use. It takes a really extreme situation for me to ever use anything but ISO 100. And I totally agree with your assessment that it's better to underexpose a shot (using exposure compensation or manual mode), then boost the levels in post-processing, than to use a higher ISO. I'm often amazed at how much detail I can pull out of the shadows, as long as the image wasn't ridiculously underexposed.

--Larry

Robert Sheldon said:

This subject was discussed on Byan Bigger's forum,
http://www.network54.com/Hide/Forum/151930 , in early to late
September. You may want to look it up there.

In my own, very brief, testing I found that, for shooting in JPEG,
I could under expose by two stops (instead of using iso 400) and in
post processing increase the exposure. I did not appear to lose
much of anything in the dark areas and there was significantly less
noise. The JPEG file size for the iso 400 photo was 50% larger
than the JPEG file for the iso 100 photo. I had a blank wall as
part of the photo. For iso 100, jpeg really compressed this, but
at iso 400 the noise prevented the large compression.

Starting then, I lower the exposure compensation first, and then if
I still need a faster shutter speed, I increase the iso setting.

Bob Sheldon

Click to expand...

The only thing I would add to your excellent example is the fact that, all things being equal, changing just the ISO setting won't change the resulting image in terms of the overall light level. In other words, it won't make the image lighter or darker (just somewhat noisier).

On the other hand, the purpose of exposure compensation is to lighten or draken the image. A negative EC will tend to darken the image; a positive EC will tend to lighten the image.

--Larry

Dewdrop1 said:

Does this help those who are still confused or is it simply pouring
salt in the wound.

Dewdrop

Larry Cunningham said:

Exposure compensation allows you to deliberately over- or
underexpose the image relative to the exposure recommended by the
camera metering.
Using exposure compensation will result in a lighter or darker
image, which probably isn't what you have in mind.

--Larry

Stardust said:

What's the difference between the two? As far as I know,
increasing ISO would produce noise while increasing exposure
compensation doens't. Is that the only difference? If so then
adjusting ISO would be useless then?

Your help is much appreciated

Stardust

Click to expand...

Click to expand...

Click to expand...

I agree with you as long as the camera is on automatic. If it is on manual and you keep the shutter speed and aperture the same, but increase the ISO, the picture will get lighter. I'm asuming that there just isn't enough light to get a decent handheld photo and that by keeping a reasonable shutter speed with the maximum aperture, the picture is too dark. If I then increase the ISO, the picture will get lighter because, with the same shutter speed and maximum aperture, the increased CCD gain will do the trick. Because of the higher noise with higher ISOs on the D7i, this is exactly how I use the camera when the natural light is too low and I can't use the flash.

I think that we are in agreement here. It's just a matter of how you look at the problem.

Dewdrop

Larry Cunningham said:

The only thing I would add to your excellent example is the fact
that, all things being equal, changing just the ISO setting won't
change the resulting image in terms of the overall light level. In
other words, it won't make the image lighter or darker (just
somewhat noisier).

Click to expand...

Looks to me like we've both been saying the same things from varying points of view, which (hopefully) helps everyone to conceptualize the principles that are involved. And you're quite correct that all my comments have assumed that the camera is NOT in full manual mode. In manual mode, changing shutter speed, aperture, or ISO will affect the overall exposure, in predictable ways.

--Larry

Dewdrop1 said:

I think that we are in agreement here. It's just a matter of how
you look at the problem.

Dewdrop

Larry Cunningham said:

The only thing I would add to your excellent example is the fact
that, all things being equal, changing just the ISO setting won't
change the resulting image in terms of the overall light level. In
other words, it won't make the image lighter or darker (just
somewhat noisier).

Click to expand...

Click to expand...

Is there anyway not to lose jpg quality in post-processing? As far as I know, everytime you save the jpg photo the quality decreased. So if post-processing is needed, the resulted jpg will be in less quality than the original?

Stardust

Larry Cunningham said:

--Larry

Robert Sheldon said:

This subject was discussed on Byan Bigger's forum,
http://www.network54.com/Hide/Forum/151930 , in early to late
September. You may want to look it up there.

In my own, very brief, testing I found that, for shooting in JPEG,
I could under expose by two stops (instead of using iso 400) and in
post processing increase the exposure. I did not appear to lose
much of anything in the dark areas and there was significantly less
noise. The JPEG file size for the iso 400 photo was 50% larger
than the JPEG file for the iso 100 photo. I had a blank wall as
part of the photo. For iso 100, jpeg really compressed this, but
at iso 400 the noise prevented the large compression.

Starting then, I lower the exposure compensation first, and then if
I still need a faster shutter speed, I increase the iso setting.

Bob Sheldon

Click to expand...

Click to expand...

There's no way to avoid losing quality if you continue to make changes and save in JPEG format. Each save means a recompression and a resulting increase in JPEG artifacts. Sometimes it takes a few successive saves to see it, but the deterioration is there and will raise its unattractive head sooner or later.

That's why I adopted the strategy of saving every image in TIFF format the very first time I make a change to it. I save the original JPEG image in an archive for safekeeping, and never touch that original. That way, no matter what dumb thing I do to the TIFF version, I can always throw away the changes and go back to the original. After I've done all my post-processing on the image, if I need a JPEG version for on-line display I then convert the final product back to JPEG.

The bottom line is that (most of) my images are born as JPEGs, are manipulated as TIFFs, and as a final step are converted back to JPEGs when necessary.

--Larry

P.S. Photoshop 7 allows you to save TIFF images with JPEG compression, just to confuse things. If I'm not mistaken, this JPEG compression is lossy just as in JPEG images, so I recommend avoiding it like the plague.

Stardust said:

Stardust

Larry Cunningham said:

--Larry

Robert Sheldon said:

This subject was discussed on Byan Bigger's forum,
http://www.network54.com/Hide/Forum/151930 , in early to late
September. You may want to look it up there.

In my own, very brief, testing I found that, for shooting in JPEG,
I could under expose by two stops (instead of using iso 400) and in
post processing increase the exposure. I did not appear to lose
much of anything in the dark areas and there was significantly less
noise. The JPEG file size for the iso 400 photo was 50% larger
than the JPEG file for the iso 100 photo. I had a blank wall as
part of the photo. For iso 100, jpeg really compressed this, but
at iso 400 the noise prevented the large compression.

Starting then, I lower the exposure compensation first, and then if
I still need a faster shutter speed, I increase the iso setting.

Bob Sheldon

Click to expand...

Click to expand...

Click to expand...

Larry, I've found more useful information in your posts than all the other posts I've read put together. This thread has been particularlu useful. Keep it up!

Thanks

Les.

Larry Cunningham said:

That's why I adopted the strategy of saving every image in TIFF
format the very first time I make a change to it. I save the
original JPEG image in an archive for safekeeping, and never touch
that original. That way, no matter what dumb thing I do to the TIFF
version, I can always throw away the changes and go back to the
original. After I've done all my post-processing on the image, if I
need a JPEG version for on-line display I then convert the final
product back to JPEG.

The bottom line is that (most of) my images are born as JPEGs, are
manipulated as TIFFs, and as a final step are converted back to
JPEGs when necessary.

--Larry

P.S. Photoshop 7 allows you to save TIFF images with JPEG
compression, just to confuse things. If I'm not mistaken, this JPEG
compression is lossy just as in JPEG images, so I recommend
avoiding it like the plague.

Stardust said:

Stardust

Larry Cunningham said:

--Larry

Robert Sheldon said:

This subject was discussed on Byan Bigger's forum,
http://www.network54.com/Hide/Forum/151930 , in early to late
September. You may want to look it up there.

In my own, very brief, testing I found that, for shooting in JPEG,
I could under expose by two stops (instead of using iso 400) and in
post processing increase the exposure. I did not appear to lose
much of anything in the dark areas and there was significantly less
noise. The JPEG file size for the iso 400 photo was 50% larger
than the JPEG file for the iso 100 photo. I had a blank wall as
part of the photo. For iso 100, jpeg really compressed this, but
at iso 400 the noise prevented the large compression.

Starting then, I lower the exposure compensation first, and then if
I still need a faster shutter speed, I increase the iso setting.

Bob Sheldon

Click to expand...

Click to expand...

Click to expand...

Click to expand...

Thanks for all the help you guys have provided. So when a photo comes out too dark, would you guys increase the exposure compensation or ISO? Increasing ISO will generate noise while increasing exp comp will lose details of dark object in the photo. I guess I'll have to choose one?

Stardust

Larry Cunningham said:

--Larry

Dewdrop1 said:

I think that we are in agreement here. It's just a matter of how
you look at the problem.

Dewdrop

Larry Cunningham said:

The only thing I would add to your excellent example is the fact
that, all things being equal, changing just the ISO setting won't
change the resulting image in terms of the overall light level. In
other words, it won't make the image lighter or darker (just
somewhat noisier).

Click to expand...

Click to expand...

Click to expand...

When a photo comes out darker than you expected, it essentially means you need to capture more light during the exposure. Increasing the ISO won't really let you capture more light, it will allow you to use a faster shutter speed (and help to prevent camera-shake blurriness) or allow you to use a smaller aperture (and increase the depth of field). Everything else being equal, it won't make your photo lighter or darker. Just noisier.

Of course, in an extreme case, a scene can be so dark that the only way to get a usable exposure is to increase the ISO. If you're trying to shoot at ISO 100 at night, for example, the shutter speed would be too slow to take a handheld shot. Your only choice then would be to either increase the ISO setting to allow faster shutter speeds, or use a tripod and not care about the slow shutter speed.

Using a positive exposure compensation will make the resulting photo lighter (again, assuming you don't make other changes at the same time and the lighting doesn't change [G]). If you don't go too overboard with the exposure compensation, you should still wind up with good shadow detail in the picture.

--Larry

Stardust said:

Thanks for all the help you guys have provided. So when a photo
comes out too dark, would you guys increase the exposure
compensation or ISO? Increasing ISO will generate noise while
increasing exp comp will lose details of dark object in the photo.
I guess I'll have to choose one?

Stardust

Click to expand...

I should have made clear in my previous response that I'm assuming you have the camera in one of the program (P, A, or S) modes, and not in full manual (M) mode. In other words, I assumed that you're letting the camera's metering determine the proper exposure.

If you're using manual mode, things work out differently. If you manually set the shutter speed, aperture and ISO, changing any one of these three controls will change the lightness/darkness of your picture. For example, changing the ISO from 100 to 200 (and leaving the shutter speed and aperture the same) will increase the exposure by one stop and result in a lighter picture.

Hope this helps more than confuses .

--Larry

Larry Cunningham said:

Of course, in an extreme case, a scene can be so dark that the only
way to get a usable exposure is to increase the ISO. If you're
trying to shoot at ISO 100 at night, for example, the shutter speed
would be too slow to take a handheld shot. Your only choice then
would be to either increase the ISO setting to allow faster shutter
speeds, or use a tripod and not care about the slow shutter speed.

Using a positive exposure compensation will make the resulting
photo lighter (again, assuming you don't make other changes at the
same time and the lighting doesn't change [G]). If you don't go too
overboard with the exposure compensation, you should still wind up
with good shadow detail in the picture.

--Larry

Stardust said:

Thanks for all the help you guys have provided. So when a photo
comes out too dark, would you guys increase the exposure
compensation or ISO? Increasing ISO will generate noise while
increasing exp comp will lose details of dark object in the photo.
I guess I'll have to choose one?

Stardust

Click to expand...

Click to expand...

[I hate it when I have to reply to my own replies because I've forgotten something ;-)]

I assumed your question referred to using the camera in a program mode, and not manual, simply because exposure compensation is meaningless in manual mode. In manual mode, you're doing your own exposure compensation, in your head, by forcing the use of a particular shutter speed/aperture/ISO combination.

--Larry

Larry Cunningham said:

If you're using manual mode, things work out differently. If you
manually set the shutter speed, aperture and ISO, changing any one
of these three controls will change the lightness/darkness of your
picture. For example, changing the ISO from 100 to 200 (and leaving
the shutter speed and aperture the same) will increase the exposure
by one stop and result in a lighter picture.

Hope this helps more than confuses .

--Larry

Larry Cunningham said:

Of course, in an extreme case, a scene can be so dark that the only
way to get a usable exposure is to increase the ISO. If you're
trying to shoot at ISO 100 at night, for example, the shutter speed
would be too slow to take a handheld shot. Your only choice then
would be to either increase the ISO setting to allow faster shutter
speeds, or use a tripod and not care about the slow shutter speed.

Using a positive exposure compensation will make the resulting
photo lighter (again, assuming you don't make other changes at the
same time and the lighting doesn't change [G]). If you don't go too
overboard with the exposure compensation, you should still wind up
with good shadow detail in the picture.

--Larry

Stardust said:

Thanks for all the help you guys have provided. So when a photo
comes out too dark, would you guys increase the exposure
compensation or ISO? Increasing ISO will generate noise while
increasing exp comp will lose details of dark object in the photo.
I guess I'll have to choose one?

Stardust

Click to expand...

Click to expand...

Click to expand...

Again thanks for your kind replies So what range of exposure compensation is used on average when shooting in indoors? What I found is the F100's flash is either not strong enough or the flash range is too short and therefore resulting a dark image. I tend to use either +0.7 or + 1.0 exposure compensation when shooting with flash. Is this a good practice?

Stardust

Larry Cunningham said:

Of course, in an extreme case, a scene can be so dark that the only
way to get a usable exposure is to increase the ISO. If you're
trying to shoot at ISO 100 at night, for example, the shutter speed
would be too slow to take a handheld shot. Your only choice then
would be to either increase the ISO setting to allow faster shutter
speeds, or use a tripod and not care about the slow shutter speed.

Using a positive exposure compensation will make the resulting
photo lighter (again, assuming you don't make other changes at the
same time and the lighting doesn't change [G]). If you don't go too
overboard with the exposure compensation, you should still wind up
with good shadow detail in the picture.

--Larry

Stardust said:

Thanks for all the help you guys have provided. So when a photo
comes out too dark, would you guys increase the exposure
compensation or ISO? Increasing ISO will generate noise while
increasing exp comp will lose details of dark object in the photo.
I guess I'll have to choose one?

Stardust

Click to expand...

Click to expand...

Stardust said:

Again thanks for your kind replies So what range of exposure
compensation is used on average when shooting in indoors? What I
found is the F100's flash is either not strong enough or the flash
range is too short and therefore resulting a dark image. I tend to
use either +0.7 or + 1.0 exposure compensation when shooting with
flash. Is this a good practice?

Click to expand...

You should keep in mind that at ISO 100 the flash range of the built-in flash on most digital cameras when set to ISO 100 is about 10 feet. This varies somewhat as you zoom the lens with full telephoto being the shortest range. This is because as you zoom in, the focal length is being made longer, but the aperture (not f stop) remains the same. Hence, the f stop is getting smaller - less light reaches the sensor. What all this means is that when you get beyond 10 feet with the flash, the lens is open as far as it will go (minimum f stop) and positive exposure compensation won't do anything because it can't; there is no bigger aperature available and, since the flash duration is shorter than the shutter speed, adjusting the shutter speed won't help. In this case, the only thing which will brighten the image is to increase the ISO setting on the camera. By the way, ISO settings on digital cameras mean the same thing as the ISO rating on film. The higher the film ISO, the more sensitive it is and you can work in darker light or at greater flash range. Of course, with higher film speeds, you get more grain in the prictures which is called noise in digital cameras.

I teach introduction to digital photography locally and what I tell my students who don't have an external flash is to zoom out to wide angle and move closer to the subject. This does 2 things: it provides a lower f stop at wide angle and you can move closer to get under the 10 foot limit. If you are taking family photos in a typical living room, you are probably further that 10 feet from your subject. Does this help you understand why your pictures are coming out dark?

If you know that the aperture is not at it's limit and your photos are too dark, the exposure compensation you mentioned is the right thing to do. The exact value depends on the particular scene. You'lll have to experiment. Also, be careful of light objects in the foreground. The camera makes an average measurement so, if there is a bright object in the foreground, background objects will be too dark. Even someone with a bald head sitting in front of you will foul up the photo. I know it, happens to me. Also, I'm sometimes the guy with the bald head who fouls up the exposure.

Well, I've written more than I intended to when I started this. I hope I haven't confused you. You might want to pick up a good book on photography which deals with the techical aspects of it.

Dewdrop