On Mon, Jun 30, 2008 at 01:38:37PM +0000, [EMAIL PROTECTED] wrote: > Underexposure and correction in conversion always results in severe noise. > Don't kow why. But I know it happens, so I avoid it . . .
It happens because noise is (by definition) pretty much random. If you underexpose by two stops, and correct in conversion, you're going to get a certain amount of noise. If, however, you expose correctly, you're going to get four times the number of photons contributing to the signal. And while you have four times as much potential for noise, that doesn't mean you're going to get four times as much noise. While only exactly true for Gaussian noise distributions, you can expect to see the amount of noise go up by roughly the square root of the exposure gain. This means that the signal-to-noise ratio gets about one stop worse for every two stops of underexposure. Ad to that the fact that for low sensor values you also get far more artifacts caused by quantization, and you want to avoid underexposure. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
