FIGURE 9. Two
imperceptibly different images (left and centre) give the image to the right
when the difference of their pixel values is calculated using Adobe Photoshop’s
“Difference” blending mode (levels subsequently adjusted). Note that this
operation will not work on the file used for screen display, because the JPEG
compression destroys the information subtly hidden in the images. To repeat the
operation, use the uncompressed file
in TIFF format (720 kB).
Copyright of photograph: The Natural History
Museum, London 1999 (Specimen image no: NHM PP DI 00075). Copyright of logotype:
Coquina Press 1998.
