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How does ISO setting work?



 
 
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  #1  
Old July 15th 05, 07:08 PM
David Arnstein
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Default How does ISO setting work?

The digital cameras that I have seen have a feature that allows the
user to choose an ISO setting. I would like to know what this feature
does, since I suspect that it is useless.

My concern is that setting a high ISO number simply
1. Causes the camera to take pictures that are quite dark
2. Post processes the picture by increasing the brightness, in
software.

If this is the case, then I prefer to increase the brightness myself,
in Photoshop.

On the other hand, if the ISO adjustment on the camera actually
changes the physical properties of the photosensor, then it's a
different story.

I'd like some feedback on this before I spend my time experimenting
with different ISO settings.
--
David Arnstein

  #2  
Old July 15th 05, 07:17 PM
Your-Nice
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Default

iso settings are to do with how sensitive your sensor is to light , the
higher the iso setting i.e 400-800 1600 means you could take a photo in a
dimmer room than iso 100 or 200.

"David Arnstein" wrote in message
...
The digital cameras that I have seen have a feature that allows the
user to choose an ISO setting. I would like to know what this feature
does, since I suspect that it is useless.

My concern is that setting a high ISO number simply
1. Causes the camera to take pictures that are quite dark
2. Post processes the picture by increasing the brightness, in
software.

If this is the case, then I prefer to increase the brightness myself,
in Photoshop.

On the other hand, if the ISO adjustment on the camera actually
changes the physical properties of the photosensor, then it's a
different story.

I'd like some feedback on this before I spend my time experimenting
with different ISO settings.
--
David Arnstein



  #3  
Old July 15th 05, 07:30 PM
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Default



David Arnstein wrote:
The digital cameras that I have seen have a feature that allows the
user to choose an ISO setting. I would like to know what this feature
does, since I suspect that it is useless.

My concern is that setting a high ISO number simply
1. Causes the camera to take pictures that are quite dark
2. Post processes the picture by increasing the brightness, in
software.

If this is the case, then I prefer to increase the brightness myself,
in Photoshop.

On the other hand, if the ISO adjustment on the camera actually
changes the physical properties of the photosensor, then it's a
different story.

I'd like some feedback on this before I spend my time experimenting
with different ISO settings.
--
David Arnstein


ISO does not change the physical properties of the photosensor, it
simply brightens the image as you suggest. There is, however, one
crucial difference. It amplifies the signal before digitizing it, and
this keeps down the quantization noise.

-T

  #4  
Old July 15th 05, 07:40 PM
Marvin
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Your-Nice wrote:
iso settings are to do with how sensitive your sensor is to light , the
higher the iso setting i.e 400-800 1600 means you could take a photo in a
dimmer room than iso 100 or 200.


Not quite correct. The ISO setting doesn't change the sensor at all. It changes the
amplification in the readout. I


"David Arnstein" wrote in message
...

The digital cameras that I have seen have a feature that allows the
user to choose an ISO setting. I would like to know what this feature
does, since I suspect that it is useless.

My concern is that setting a high ISO number simply
1. Causes the camera to take pictures that are quite dark


The picture won't come out dark unless oyu use the wrong ISO setting. Most digicams let
you use auutomaic ISO setting as part of a point-and-shoot setting. It works properly
most of the time.

2. Post processes the picture by increasing the brightness, in
software.


No. it increases the amplification by the camera's electronic hardware.

If this is the case, then I prefer to increase the brightness myself,
in Photoshop.


You can do that up to a point. If the exposures are really bad, Photoshop or any progam
can't do the job well.


On the other hand, if the ISO adjustment on the camera actually
changes the physical properties of the photosensor, then it's a
different story.

I'd like some feedback on this before I spend my time experimenting
with different ISO settings.
--
David Arnstein



My suggestion to you is to not think of digital photography as a close analog of film
photography. It is more diferent from film than film is from tintype. Each technology
has its own advantages and drawbacks. The more you understand the one you are using, the
better the results you will get.
  #5  
Old July 15th 05, 11:40 PM
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Default

In message ,
(David Arnstein) wrote:

The digital cameras that I have seen have a feature that allows the
user to choose an ISO setting. I would like to know what this feature
does, since I suspect that it is useless.


My concern is that setting a high ISO number simply
1. Causes the camera to take pictures that are quite dark


That should not be a problem. If anything, high ISO images should be
brighter if they are different in brightness, either because there is
not enough light for a low ISO image, or the cameras has run out of
shutter speeds or wide aperture to keep the high ISO image from
over-exposing.

2. Post processes the picture by increasing the brightness, in
software.


Some cameras achieve their highest ISOs this way, and get the lower
range by varying the gain applied to the sensor capture before it is
turned into numbers. Perhaps some do all of their ISOs this way, but I
don't know how many.

If this is the case, then I prefer to increase the brightness myself,
in Photoshop.

On the other hand, if the ISO adjustment on the camera actually
changes the physical properties of the photosensor, then it's a
different story.


The normal way does not change the sensor at all; the sensors are fixed
in their sensitivities. The difference between ISOs is usually achieved
by amplifying the signal by different amounts, causing different ranges
of sensor voltages to map to the range of RAW data, usually 0 to 4095.

I'd like some feedback on this before I spend my time experimenting
with different ISO settings.


Experimenting will tell you more than other people usually can, and more
than what the manufacturer will tell you.

If the camera has manual exposure, set it up on a tripod or table to
take an image with a full range of tones, and make a normal exposure at
the camera's highest ISO. Now, keep the f-stop and the shutter speed
the same, but set it to the lowest ISO. Boost the exposure level of the
low-ISO image in software to match the high-ISO. If the high-ISO image
has less noise and more detail, then the camera may be using
amplification in hardware, and then you are clearly better off using
high ISO than under-exposing a low ISO image (or having too long a
shutter speed at a low ISO). Even if the camera is using amplification,
if it is JPEG-only, it may be that the camera kills shadow detail when
making a JPEG, to hide noise, in which case you will get poor images if
you boost the exposure, anyway. You can also try the different ISOs
with the same image, and automatic exposure. If the quality
deteriorates rapidly as you go to higher ISOs, then there is probably no
amplification. If the quality is only a little bit worse at each higher
ISO, there is probably amplification. It is also possible that there is
amplifiaction, but it has a lot of noise and distortion.

This is a complex issue, with usually no details coming from the
manufacturer.
--


John P Sheehy

  #6  
Old July 15th 05, 11:41 PM
Matti Vuori
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Could you please post in one group only...

--
Matti Vuori, http://sivut.koti.soon.fi/mvuori/index-e.htm

  #7  
Old July 16th 05, 12:31 AM
David Arnstein
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Default

In article ,
Matti Vuori wrote:
Could you please post in one group only...


I love usenet and I endeavor to be a "good citizen" in this space. I
am very interested in your post.

Would you please explain your reasoning. Here is mine:

1. My post is relevant to all three news groups.
2. By cross-posting, I arrange that an individual using a decent
newsreader will only see my post once, even if he habitually reads
all three news groups.

I look forward to your response Mr. Vuori.
--
David Arnstein

  #8  
Old July 16th 05, 12:40 AM
Andy Sullivan
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"David Arnstein" wrote in message ...
In article ,
Matti Vuori wrote:
Could you please post in one group only...


I love usenet and I endeavor to be a "good citizen" in this space. I
am very interested in your post.

Would you please explain your reasoning. Here is mine:

1. My post is relevant to all three news groups.
2. By cross-posting, I arrange that an individual using a decent
newsreader will only see my post once, even if he habitually reads
all three news groups.

I look forward to your response Mr. Vuori.


I think Matti's post equates to, "I'm not using a decent
news reader and don't know how Usenet works."



  #9  
Old July 16th 05, 08:19 AM
David J Taylor
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Default

David Arnstein wrote:
In article ,
Matti Vuori wrote:
Could you please post in one group only...


I love usenet and I endeavor to be a "good citizen" in this space. I
am very interested in your post.

Would you please explain your reasoning. Here is mine:

1. My post is relevant to all three news groups.
2. By cross-posting, I arrange that an individual using a decent
newsreader will only see my post once, even if he habitually reads
all three news groups.

I look forward to your response Mr. Vuori.


Following that line of reasoning, isn't your post relevant in
rec.photo.digital.zlr as well?

But your reasoning is flawed. If something is of general interest, it
should only be in rec.photo.digital. The aim of splitting the newsgroups
was to reduce the number of postings, and help people focus on their own
interest better. There was no intention to replace the rec.photo.digital
group.

It would be better to restrict your posting to just one group if possible.

Thanks,
David


  #10  
Old July 16th 05, 09:31 AM
Ron Hunter
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Posts: n/a
Default

David Arnstein wrote:
The digital cameras that I have seen have a feature that allows the
user to choose an ISO setting. I would like to know what this feature
does, since I suspect that it is useless.

My concern is that setting a high ISO number simply
1. Causes the camera to take pictures that are quite dark
2. Post processes the picture by increasing the brightness, in
software.

If this is the case, then I prefer to increase the brightness myself,
in Photoshop.

On the other hand, if the ISO adjustment on the camera actually
changes the physical properties of the photosensor, then it's a
different story.

I'd like some feedback on this before I spend my time experimenting
with different ISO settings.


Vastly oversimplified:
The ISO number is like an amplifier volume setting. The larger the
number the 'louder' the light output from the sensor. And, like a sound
amplifier, excessive settings often produce very distorted, and
'clipped' output. The lower the ISO setting, the more light you need
for a usable picture, but the higher the setting, the more the output
from the sensor is amplified, and the more 'noise', and 'distortion' you
will see. Many cameras use software to improve the image quality, and,
since they have access to the original output from the sensor, they can
usually do this better than Photoshop.


--
Ron Hunter
 




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