Compare PHASH: Reference for how it was implemented?

[IMUser78]

Dear all,

Imagemagick implements the PHASH (percetual hash) algorithm in the compare command. It is not clear, however, how the PHASH was specifically implemented. Does anyone have a reference to an article or publication that was used as the basis for the implementation?

Thank you!

[snibgo]

For references, see Fred's paper http://www.fmwconcepts.com/misc_tests/p ... index.html

Since he wrote that, the IM implementation has changed to allow for different colorspaces to be used, instead of sRGb and HCL.

[fmw42]

The reference in the link to my web site that was used is http://www.naturalspublishing.com/files ... g3omq1.pdf