Matthew Finlay wrote: Hi,

Can anyone point me to an equation or algorithm for calculating the delta H between two Lab values?

depends on what you are trying to use it for. As written above, you can simply convert to LCh and subtract the h's modulo 180 degrees.

Can I simply set L1 to equal L2 (making the L component the same in both samples) and then calculate the delta-E using my specified method?

but if you are trying to compute the hue delta E component, then the usual method is to compute the total Lab delta E squared, subtract the delta L squared and the delta C squared, and take the square root. (You can of course simplify the above to be a computation using just a* and b* easily enough.) Graeme Gill.