Archived posting to the Leica Users Group, 2004/04/19
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Presumably we are talking an ideal scanner here. Anyways. I THINK (again don't take this as gospel) that the gamma function works backwards in the scanner. So the negative density values are encoded into your image data using an inverse gamma function. output value = input value ** -gamma This is very simplified because the scanner itself is not a linear device unless it has been profiled, and it only has so many bits of resolution, and all that. Moreover one normally sets black and white points in the scanner software (and sometimes hardware) which changes all the relationships since it shifts zero density to the fog base and infinite density to the Dmax. In order to use a scanner as a densitometer you have to do some head scratching. On Apr 19, 2004, at 4:59 PM, Saganich, Christopher/Medical Physics wrote: > Since the input and output values are linear (between 0 and 1) how is > this related to negative density? Is there a mathematical > relationship between the log base 10 density the input/output. Or > perhaps I'm trying to compare apples and oranges? -- John Brownlow Deep Fried Films, Inc http://www.johnbrownlow.com http://www.pinkheadedbug.com