Archived posting to the Leica Users Group, 2004/04/19[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]
Thanks John, OK, if I scan a neg which was made using source of luminescence 16 c/ft2 I would have a neg density of 1.2 and the histogram should show then 127 peak with 8 bit, if I account for the screen gamma. 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? Chris Saganich -----Original Message----- From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of Johnny Deadman Sent: Monday, April 19, 2004 2:27 PM To: Leica Users digest Subject: [Leica] Photoshop Questions 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 _______________________________________________ Leica Users Group. See http://leica-users.org/mailman/listinfo/lug for more information ===================================================================== Please note that this e-mail and any files transmitted with it may be privileged, confidential, and protected from disclosure under applicable law. If the reader of this message is not the intended recipient, or an employee or agent responsible for delivering this message to the intended recipient, you are hereby notified that any reading, dissemination, distribution, copying, or other use of this communication or any of its attachments is strictly prohibited. If you have received this communication in error, please notify the sender immediately by replying to this message and deleting this message, any attachments, and all copies and backups from your computer.