Is ISO the only determinant of noise?

[ANAYV]

Does exposure compensation do the same?

ANAYV

BC

The effect of overall exposure on noise is often misunderstood.
Increasing exposure, in general, does not decrease noise and
actually increases noise. However, it reduces your percpeption of
noise because brighter areas will have a higher signal to noise
ratio.

Thanks Ron for an excellent post.

I think that noise seen in higher ISO shots has also something to
do with what Ron described above. But to be more specific, I think
that the ISO setting is actually a GAIN setting. Otherwise it would
be impossible to get the same exposure with i.e. 1/60,F2 @ISO 50
and with 1/500,F2 @ISO400. Any why do I think this? Because the
sensor is the same. I don't think that the sensitivity of the
sensor can be increased per se. Correct me if I'm wrong.

And what all this got to do with what Ron said in his earlier post?
If ISO setting is actully a GAIN setting, by incresing gain in
image we will end up increasing the electric noise in it as well,
and thus signal-to-noise ratio decreases.

What do you think?

-tepa

 

[Tepa]

Does exposure compensation do the same?

Since digital cameras don't really have film's ISO speeds, the ISO
setting in a digital camera really refers to boosting or lowering
the CCD's sensitivity to light (IE Gain). The problem with gain is
that as the sensitivity level is raised, it produces noise
(unwanted electronic artifacts in the picture, such as random white
splotches or streaks), just as turning up the volume on a radio
increases the amount of static you can hear in the background.
Therefore, digital camera users should view gain in the same way
that photographers look at ISO speed: turn it up when you need
faster speeds or must shoot in low light, but be prepared for some
image degradation.

BC

ANAYV,

actually no. When using the exposure compensation you change the shutter speed value. By using exposure compensation you tell the camera to what tone you want the metered color/light end up in the resulting image. Camera takes you wish into account by changing the shutter speed. My G3 shows the new shutter speed, check if your camera does the same. (If camera changed the aperture it would change the impression the photographer wanted -not good).

But note, this doesn't increase noise, as no additional electric amplification is used.

-tepa