Archived posting to the Leica Users Group, 2004/04/19
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Saganich, Christopher/Medical Physics said the following on 4/19/2004 10:26 AM: > Can anyone explain the units used in the grey histogram, specifically the "Level", (O- 256) and how this might relate to opacity, density or luminescence from a densitometry or sensitometry perspective? I can't see a relation but there should be one. For example how does the 18% grey relate to the number 127? > ... I was wondering about that myself, so I Googled around a bit, and came to the conclusion that, like all simple questions, this one has no simple answer. 18% grey refers to the reflectivity of a grey card, and is not actually a neutral grey, to boot. The visual appearance of an RGB value depends on the color space in which the value is defined, as well as the output device that is used to represent the RGB value. A level of 0 in a grey histogram is the lightest shade that your output device can display (or that your input can capture at whatever settings you have is set for. A level 255 is the darkest. The value of anything in between depends on the gamma of the device. A couple of the sites that I found to confuse myself were: http://www.kodak.com/US/en/motion/products/tools/colorist.shtml http://www.aim-dtp.net/aim/calibration/middle_gray/ Lagavulin is about 238,181,53 -- but it tastes better than that. I have no idea what I am talking about. This is posted in the hope that it will enrage someone who does know this stuff enough to post a rebuttal. -- Clive http://clive.moss.net