April 02, 2021

VueScan Support for Film Types

VueScan first started supporting different film types about 20 years. We originally got film profiles from the PhotoCD database. These film profiles contain ‘sensitometric curves’ for different film types, and they don’t vary much in film types in use in the past 15 years or so.

More significantly, most color negative films have dyes that fade differently over time for each of the three color layers. This makes scans of older color negative films have a color tint that doesn’t reflect the original. This means it’s not practical to use film profiles to get accurate color.

Instead, we’ve developed the ‘Filter | Restore fading’ option, which compensates for different rates of fading of different dye colors. It does this by trying to linearize the colors that are close to neutral (gray). It works pretty well with old color negative films as well as old Ektachrome slides that have faded to red (Kodachrome dyes don’t fade much over time).

In extreme cases, the ‘Filter | Restore colors’ option is useful, but it sometimes produces strange colors. It works by finding colors closest to ‘memory colors’ – i.e. you remember that the sky is blue, grass is green, wood is brown, etc. – and then VueScan finds a color transform matrix that brings the scanned colors closest to the memory colors.

Black and white film is different, since it doesn’t have color dyes, but only has silver particles that determine how gray the image is. Depending on how the film was developed, the contrast changes. The PhotoCD data we’re using for Kodak TMAX film has options that look like ‘CI = 0.50’ which Kodak calls this the “Developer Contrast Index”. Use film profiles with different ‘CI’ values to change the apparent contrast of the scan.

Other black and white negatives films, including the popular Ilford negative films, have sensitometric curves very close to Kodak TMAX, so you can just use the TMAX profiles with different ‘CI’ values with these films. You can also change the overall contrast of a film scan using the ‘Color | Brightness’ option. This effectively changes the slope of the sensitometric curve.