On 05/07/06, Toralf Lund <[EMAIL PROTECTED]> wrote: > I think you missed my point. As far as I know, a digital sensor's > sensitivity to light is constant. The camera will usually have a > "sensitivity" or "ISO" setting, but what that really adjusts, is a gain > applied to the signal after it leaves the sensor. Furthermore, I'm quite > sure it is correct that you get the best data quality if the exposure > etc. is set up so that the sensor is nearly saturated, but not quite. > But, that is not the same thing as saying that the digital data, or even > the analog signal after the gain stage needs to be that way. The way I > understand things, the camera's histrogram function shows the digital > data - not the actual sensor output - and I don't necessarily need to > keep that "to the right". Rather than "overexposing" the digital data, > then making it darker in Photoshop or whatever, you can do the > "darkening" already in the gain stage simply by reducing the ISO value. > > Differently put, I'm sure it is a good idea to keep the *sensor's* > histogram (if you can make one) as far to the right as possible, but > rather than moving the *digital data's histogram* to get what you want, > you can just change the ISO setting of the camera. Essentially it is > just a question of whether you want to do the exposure correction (if > you can call it that) on the digital data or in the analogue world. I > would intuitively choose the latter approach in most cases, but there > could of course be some specific reason to prefer the former... > > Even more differently put, isn't what people are saying here just a > rather convoluted version of "you get less noise with a lower ISO setting"?
Hi Toralf, I'm going to de-lurk and try and answer here. Quick answer : No! Long answer : Yes, you get less noise with a lower ISO setting, but that wasn't really what people were trying to say here. The point is that you *also* get less noise if you push the histogram of the *digital* data to the right. It is that digital data that you need to try to saturated towards its maximum values to minimize noise in the digital domain. Godfrey's previous post (and the luminous landscape link someone posted) explains very clearly the mechanism by which this digital noise can be reduced int his way. > I don't know if I'm making it entirely clear what I'm talking about > here... Don't worry, your question was very clear! Eric. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
