Due to how ImageMagick handles its image format conversion and how Tempfile handles its naming scheme, it is necessary to override how Tempfile makes its names so as to allow for file extensions. Idea taken from the comments on this blog post: marsorange.com/archives/of-mogrify-ruby-tempfile-dynamic-class-definitions

Methods
Public Instance methods
make_tmpname(basename, n)

Replaces Tempfile‘s make_tmpname with one that honors file extensions.

[ show source ]

    # File lib/data_base/attachment/processor.rb, line 43
43:       def make_tmpname(basename, n)
44:         extension = File.extname(basename)
45:         sprintf("%s,%d,%d%s", File.basename(basename, extension), $$, n, extension)
46:       end