The color difference method of the Color Measurement Committee (the CMC) is a model using two parameters *l* and *c*,
typically expressed as CMC(*l:c*). Commonly used values for acceptability are CMC(2:1) and for perceptibility are CMC(1:1).

The color difference, or ΔE, between a sample color L_{2}a_{2}b_{2} and a reference color L_{1}a_{1}b_{1} is:

where

**Implementation Notes:**

*H*is in degrees, not radians._{1}- If
*H*< 0°, add 360° to it._{1} - In computing
*H*, be careful with the inverse tangent since_{1}*a*could be zero. Instead, use special math functions to do this. In both the Standard C library and Java, this function is called**atan2**. In Microsoft Excel, it is called**ATAN2**. These special functions will compute the proper inverse tangents without needing to worry about "divide by zero" conditions. Additionally, atan2 will also handle the quadrants for you.