If you look at 100-year-old black-and-white images, you can't help noticing the sepia tint. The black areas in particular are likely to have yellowed significantly over the years, whereas the lighter hues will only have a slight tint. On my last trip to my home country, Germany, I had the idea of converting a couple of shots I had taken there with my digital camera (Figure 1) into black-and-white and aging them artificially (Figure 2), just to illustrate how much more colorful I perceive the scenery in my current residence, San Francisco.

According to Wikipedia [3], the sepia tint of old photographs comes from a pigment that was used in photography as of the late 19th century. It was taken from a cuttlefish that is indigenous to the English Channel and that has the official Latin name Sepia officinalis. To achieve the same effect with digital images, the artist has to tint the darker parts of the image yellowish brown (Figure 3). The colors at the middle of the spectrum are not greatly affected by this, and the light parts not at all.

It is not sufficient to simply remove the color information from the image and dye it yellow uniformly – to be convincing, more subtle measures are needed. Digital photo specialist Eric Jeschke published a number of GIMP operations [4], which, if applied in sequence, produce convincingly original "pre-war" pictures. The CPAN Gimp Perl module lets you combine the individual steps as a Perl script, which you can then run against a number of photos.

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