Archived posting to the Leica Users Group, 2004/04/19
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]That depends on a lot of things, not least the gamma with which the image is encoded, which changes the grey point. Don't take this as gospel, but my understanding is: Output Value = Input Value ** Gamma Where both input and output values are between 0 (black) and 1 (white). The higher the gamma, the darker the midtones. What this means is that 50% grey (127 in 8-bit images) represents the following grey values, depending on gamma: 50% grey in linear gamma (Gamma = 1) 28% grey in Gamma 1.8 (Mac standard) 22% grey in Gamma 2.2 (Windoze standard) 18% grey in Gamma 2.5 (often used as a standard for uncorrected CRTs) On Apr 19, 2004, at 11:26 AM, Saganich, Christopher/Medical Physics wrote: > 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? -- John Brownlow Deep Fried Films, Inc http://www.johnbrownlow.com http://www.pinkheadedbug.com -- John Brownlow Deep Fried Films, Inc http://www.johnbrownlow.com http://www.pinkheadedbug.com