Toralf Lund wrote:
> Digital Image Studio wrote:
>
>> On 24/08/07, Toralf Lund <[EMAIL PROTECTED]> wrote:
>>
>>
>>
>>> Isn't the ISO rating (of the sensor) directly linked to the
>>> signal-to-noise ratio? [ ... ]
>>>
>>>
>>
> what I was trying to say, is that I think I've
> read somewhere that the "real" ISO is related more to the
> signal-to-noise than the saturation level, i.e. that it may be defined
> as the amount of exposure needed to reach a certain signal-to-noise
> ratio, or something.
>
Actually, Wikipedia says:
ISO Standard 12232:2006
<http://www.iso.org/iso/en/CatalogueDetailPage.CatalogueDetail?CSNUMBER=37777>
("Photography — Digital still cameras — Determination of exposure
index, ISO speed ratings, standard output sensitivity, and
recommended exposure index") defines ISO speed in terms of the
amount of light needed to achieve a certain "quality" in the sense
of a per-pixel signal-to-noise ratio.
but also
However, this standard ISO speed "rating" for a digital camera is
not necessarily very related to the ISO "setting" or "exposure
index" used on the camera.
As I suggested earlier, I always thought that what was referred to the
native ISO of the camera was the actual rating according to the ISO
spec, and that selecting another ISO value in reality only meant that
the signal from the sensor was amplified by (setting/native ISO), but
perhaps it's not quite as simple as that...
The actual ISO standard is not available for free, of course.
- Toralf
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