The gamma can be controlled by choosing different films, or by varying the development time or temperature.
In digital photography, image sensors tend to be nearly linear, but these nonlinear tone reproduction characteristics are emulated in the camera hardware and/or processing software, via "curves".
It is easier to demonstrate the need for a TRC using halftoned printing methods such as inkjet, or xerographic technologies.
To compensate for this darkening, a TRC is applied and the digital image's reflectance value is reduced to something less than 50% dot coverage.
For example, by default, when transforming from L*A*B* to CMYK, Photoshop applies an ICC profile for SWOP standard inks and 20% dot gain for coated paper.