A grayscale illustration from a scanned book having the noisy paper texture removed and converted to greyscale using the following Imagemagick command:
<dl><dd><tt>convert foo.ppm -level-colors 'rgb(40,40,40),rgb(180,180,160)' -type Grayscale foo.jpg</tt></dd></dl>
<bdi><a href="https://en.wikipedia.org/wiki/en:Franz_Reuleaux" class="extiw" title="w:en:Franz Reuleaux"><span title="German mechanical engineer">Franz Reuleaux</span></a>
</bdi>
1876
<a rel="nofollow" class="external free" href="https://archive.org/stream/kinematicsofmach00reuluoft#page/46/mode/2up">https://archive.org/stream/kinematicsofmach00reuluoft#page/46/mode/2up</a>