That doesn't help. You're still reducing a continuous spectrum to a single sample value. Whether that's still just at the single sensor site in the RAW file, or has been interpolated to a component in an RGB value, makes no difference.
Consider that 'yellow light or red/green light' case again. There's nothing you can do with the sensor values to differentiate between a monochromatic light source or a broad-spectrum source, and yet without that information you can't predict how any real film will respond. Fortunately the sensitivities of the various layers in colour films (and the different sensors in the digital sensor array) are all fairly close to the spectral sensitivities of the human eye (gee - I wonder why that should be the case? :-), so ignoring this issue and just dealing with overall hue and saturation will get you something fairly close. You could even argue that not reproducing the way that certain shades of orange tended to show up as purple on some films is a plus - you're recreating the ideal version of the film as it should have been, not how it actually behaved. On Tue, Jan 24, 2006 at 02:10:34PM -0600, Gonz wrote: > It sounds like the ideal place to do some type of film characteristic > mapping is through the RAW sensor data, before it has been combined > through the Bayer interpolation. I.e. modify the Bayer mechanism to > mimic a film type. > > rg > > > John Francis wrote: > >But that's not really enough to reproduce a film characteristic. > > > >As we all know, colour film (and the human eye, and digital > >sensors, and digital colour spaces) are tri-stimulus systems; > >any particular colour is reduced to three measured values. > > > >The real world, though, is not so discrete - it's possible > >for the same value triple to be produced by different inputs. > >For a very simple example, consider a bright yellow light. > >This may be a monochromatic light source, emitting light > >at one very specific frequency, or it maybe a combination > >of red and green light sources, or any number of different > >options. But by the time it is reduced to a value triple, > >there's no way to differentiate between any of the original > >light spectra that map to the same triple of sample values. > >(This is technically known as metamerism). > > > >But (and it's a very important but) the mapping to triples > >depends on the frequency response of the sensor - it's not > >an absolute. To continue the analogy of a pure yellow light > >versus a combination of red and green, two different colour > >films may very well behave differently; the perceived colour > >of the red/green combination may match the monochromatic > >yellow light on one film, and yet appear to be a different > >colour on the other film. Photographers have long known > >this, and have chosen different films for different purposes. > > > >Once two real-world lighting conditions have been mapped to > >the same recorded tri-stimulus values, though, there's nothing > >you can do split them apart again. Given an image recorded > >on the first film, and showing that yellow light source, > >there's just no way for you to map it to the right colour > >to mimic the behaviour of the second type of film. > > > > > >On Tue, Jan 24, 2006 at 06:52:20AM -0500, Paul Stenquist wrote: > > > >>With enough time and patience, you can copy any tint/saturation > >>level/contrast level through digital manipulation. > >>Paul > >>On Jan 24, 2006, at 2:00 AM, Scott Loveless wrote: > >> > >> > >>>I just spent some time looking through some portraits taken with > >>>Kodachrome 25 from the late 70s or early 80s. That's right, > >>>portraits. The color is amazing. Anyone have a recommendation how I > >>>might achieve this look today? > >>> > >>>-- > >>>Scott Loveless > >>>http://www.twosixteen.com > >>> > >>>-- > >>>"You have to hold the button down" -Arnold Newman > >>> > > > > > > -- > Someone handed me a picture and said, "This is a picture of me when I > was younger." Every picture of you is when you were younger. "...Here's > a picture of me when I'm older." Where'd you get that camera man? > - Mitch Hedberg
