This seems more like a comparative study, but I find the ideas of manufacturers about what exactly is "sepia" very surprising!
The original black and white photo is an attempt to digitally imitate a pseudo-solarization. At the moment I'm busy transferring all the info from my old laptop to a new one and I met a number of (free) editing programs that I don't use that much anymore. I searched those programs for the "sepia button" and found most of them!
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original B&W photo
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I know several members (Mac users) on this forum use GIMP, a very good program but I just have too little patience to get the most out of it.
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How about this: I've been using (free) XN View for 10 years as the 'standard' to open/view photos on my computer and have never known it's possible to use this program to give photos a sepia tone.
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PhotoScape is a program I've been using for 12 years now, it is really an amazing (free) program you must download immediately, discover all the possibilities and I am sure you will never delete it again!
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Not free, so exception, but for the finishing touch to my fisheye images of trees, I started to use Artweaver quite some time ago, a drawing program instead of a photo editing program.