Media tab

This tab lets you specify the film type and the color mask values (if you want to lock the orange mask color for negatives).

Slide/Negative/B/W vendor/brand/type

Use these options to set up the film type for various settings for the "Device|Media type" option.

Auto mask

Use this option to automatically compute the color mask value for each scan. The color mask is the maximum color of a piece of film or reflective image. This maximum value is used to set the film color for 100% black on negatives, and the film color for 100% white on slides and reflective prints.

An advanced technique is to scan a piece of unexposed negative or overexposed slide and then turn off the "Auto mask" option. This will lock the value for the color mask so you can have a consistent value for an entire roll of film. Otherwise, scanning an overexposed negative or underexposed slide may automatically compute a value that's too small, resulting in subtle color shifts.

Mask red/green/blue

This option lets you manually enter values for the color mask. This is primarily useful if you're scanning a series of negatives or slides from the same roll of film.