We are in agreement! :- ) Harvey Ferdschneider partner, SKID Photography, NYC
Bill Fernandez wrote: > Hi Harvey-- > > "25mm" was a typo, sorry. I meant "35mm". > > I scanned a 35mm Kodak Q60 Ektachrome calibration target at 1200dpi > on a flatbed scanner. Then I scanned a 4x5 inch Kodak Q60 Ektachrome > calibration target on the same flatbed scanner, again at 1200dpi. > > The grey steps are supposed to be the same density on each target > (Except for manufacturing tolerances). > > If in Photoshop you select a rectangular area covering, say, 90% of > one of the grey steps and open the Histogram window it will display > (among other things) a standard deviation number which represents how > widely the pixels within the selection vary in tone from one another. > This is a good way to see at what density levels the scanner starts > getting noisy: just move the selection from one grey patch to the > next and record the standard deviation of each step. At some point > the standard deviation will start to rise, implying that those steps > are noisier than the previous ones because there's more variation in > the value of the pixels. > > Now when I did this on both of the above targets (remembering in each > case to select the same percentage of each grey patch) I found that > the standard deviations on the 35mm target's grey patches rose faster > and higher than on the 4x5 inch target's. > > Initially I was perturbed until I realized that this was like taking > a picture of the exact same scene on both 35mm and 4x5 film and > making, say, 20 x 30 inch prints from both slides. The grain of the > 35mm slide gets blown up five times as much as that of the 4x5 inch > slide. I'm assuming that having big blobs of grain (35mm target) > rather than a fine pattern thereof (4x5 target) has skewed the > distribution of tones reflected in the standard deviation numbers: > that to the histogram the grey patches look less uniformly grey on > the scan of the 35mm target than the 4x5 target. > > --Bill > > At 11:27 PM -0400 23-10-01, SKID Photography wrote: > >Bill, > >Maybe then I'm not understanding you. If what you are saying is > >true, then the 25mm sample is not the same > >density as the larger format, because of the grain (or more > >properly, the space between the grain). > > > >Harvey Ferdschneider > >partner, SKID Photography, NYC > > > >Bill Fernandez wrote:- > > > >> So according to your summary of the discussion on the ColorSync list > >> they decided that the artifacts being discussed were caused by > >> scanner noise in dense areas. Certainly a well-known phenomenon. I > >> on the other hand was referring to an instance where I caught myself > >> erroneously attributing the effects of film grain to scanner noise. > >> As far as I can tell we were talking about two different things. > >> > >> --Bill > >> > >> >At 1:39 PM -0400 23-10-01, SKID Photography wrote: > >> > > >> >The threads on the colorsync list... > >> >The consensus of most was that the grain that was showing up in the > >> >dense shadows from the greater > >> enlargements (samples) was due to the problem of electronic noise, > >> and not, in fact grain... > >> > >> >Bill Fernandez wrote: > >> >...I couldn't understand why > >> > > two targets of equal density on the same scanner could be so > >> >> different; until I inspected both scans closely and realized that the > >> >> 25mm target was hugely grainy, especially in the dense end of the > > > >> greyscale. So what at first I thought was scanner noise turned out > > > > > to be film grain > > -- > > ====================================================================== > Bill Fernandez * User Interface Architect * Bill Fernandez Design > > (505) 346-3080 * [EMAIL PROTECTED] * http://billfernandez.com > ======================================================================
