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 > >
