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One of the undergraduates in my lab showed up one day with a copy of the book Dracula, by Bram Stoker, from Barnes & Noble. The title was in a blackletter typeface and I immediately suspected I could make an ambigram out of it. The typeface, however, had some embellishments I wanted to preserve (flourishes, hashed highlighting, outlining, bat wings, etc.), so rather than just jump in and try to make an ambigram of the word Dracula with a typeface I already have, I borrowed the book and scanned the cover. Then I took that image and converted it to a vector graphic.
This is what it looked like on the original cover. I thought the D and the A would be easily interchangeable; the R and L would be a little tougher, but doable; and the A and U wouldn't give me too much trouble. So the only real difficulty would be in making the C compatible with itself.
I was right. This was the best I could come up with. I'm not happy with it, though, since this trick makes the C look sort of like an S.
So I tried a different configuration where the letters aren't in a one-to-one concordance. The result was a lot more cramped and, ultimately, I felt, less readable. I also added some extra flourishes and bat wings that made the final result a bit wider.
I also tried doing one from scratch. It had the same basic problem with the C. I originally drew it with the letters separated. But after scanning it and tracing it as an .svg file I thought it looked a little funny. So I tried reducing the space between the letters and liked the outcome a little better. It's still not a great ambigram, in my opinion, though.
This next one is the logo of a web comedy called The Guild. It is about a woman who is addicted to an online role-playing game. One day I was looking at their logo  and realized that it would be pretty easy to adapt into an ambigram. The G and the ld were easy to adapt, but the u and the i were a little more challenging. Even though the i in the original wasn't dotted, I decided to do so to make the ambigram more readable.
This next one makes reference to the television series Avatar. To emphasize Aang's ability to use all four classical elements, I colored it white (air), blue (water), brown (earth), and yellow (fire). I think this is the cleanest ambigram of this batch. (But it's also not really based on a pre-existing logo since the logo for the television show is just composed of uneven brush strokes.)
Here is a nod to the novel Mistborn, by Brandon Sanderson. This one also came about by staring at the cover of my book long enough to notice its ambigrammatic potential. I even tried to emulate the lettering of the cover of the edition I bought  both in letterform and in color pattern. I thought that ligating the t and the b to make the o was clever, but the result is a little hard to read.
Last, but not least, I took the stylized title card from the Harry Potter film franchise and turned it into an ambigram. This one started as a doodle  and then I decided to go back and use the original lettering. The rr/o combination gave me the most trouble—the rr looks kind of like a u and the o looks kind of like an a (i.e. Hauy Patter). And I had to change the e to an E.
 See my other ambigram drawings here and here.
 You can view or purchase it here.
 If you're unsure what a vector graphic is, see my post Raster Graphics and Vector Graphics. Using Inkscape, to convert a raster graphic to a vector graphic, first choose File, then Import… Navigate to your raster graphic file and open it. I always choose to embed the image, even though this makes the .svg file larger. Now, with the raster graphic selected, go to Path, then Trace bitmap… This will open up a new window with options. For this project I did Multiple scans using the color option, with the number of scans set to 3 and I deselected the default option Stack scans. Hit OK and it will render the raster graphic to vector paths. I then chose Object and Ungroup to separate the different colors. The only one I wanted to work with was the black scan, so I moved that one and then deleted the other two scans and the raster graphic.
 You can watch the series at http://www.watchtheguild.com/. The series is pretty funny. Be warned, though, that in the first season and possibly the second, one of the characters, Tinkerbella, has a potty mouth and her language isn't bleeped out. Another character, Zaboo, sometimes says lewd things. So watch at your own discretion.
 You can see it at the top of the cover of this comic book cover.
 Read my reviews here, here, and here (as well as the feature film, The Last Airbender, reviewed here).
 I guess you could make the argument that this works for the movie Avatar (read my review here), too, since the Na'vi have white and blue skin, yellow eyes, and brown or black hair. But that wasn't my intention.
 Read my review of Mistborn: The Final Empire here. The reviews for the sequels are forthcoming.
 You can see it here.
 Here is the original doodle:
The original cover for the Barnes and Noble is presumably © 2011 Barnes & Noble, Inc. All rights reserved. It is used here only for illustrative purposes. The derivative ambigrams I have created are for entertainment only and are not intended to violate any copyrights retained by Barnes & Noble, Inc. This copyright notice supersedes the Creative Commons license used to copyright the text of this blog post.
The original logo for The Guild is © 2011 The Guild. All rights reserved. The derivative ambigram I have created is for entertainment only and is not intended to violate any copyrights retained by The Guild. This copyright notice supersedes the Creative Commons license used to copyright the text of this blog post.
The original cover for Mistborn: The Final Empire is © 2011 Tor. All rights reserved. The derivative ambigram I have created is for entertainment only and is not intended to violate any copyrights retained by Tor. This copyright notice supersedes the Creative Commons license used to copyright the text of this blog post.
The original title card for Harry Potter is presumably © 1998 Arthur A. Levine Books. All rights reserved. The derivative ambigram I have created is for entertainment only and is not intended to violate any copyrights retained by Arthur A. Levine Books. This copyright notice supersedes the Creative Commons license used to copyright the text of this blog post.