# Best color difference or distance approximation?

Currently, a standard way of comparing colors is using "Delta E" metric in CIELab [Color-difference] which is based on Euclidean distance in CIELab color space.

However, for certain applications using the distance metric intensively "Delta E" metric could be a bit slow (e.g. RGB2Lab conversion is necessary, floating point operations can be costly, etc.).

Is there a "good enough approximation" of color difference or distance?

Ex.

How about cosine distance (i.e. the angle between two color vectors)?

@Guanta Thanks for the comment. Can you elaborate why you think cosine distance might be a "good enough approximation" of color difference or distance? It does have the speed potential as reported in EVALUATION OF SIMILARITY MEASUREMENT FOR IMAGE RETRIEVAL...

Comprehensive Survey on Distance/Similarity Measures