The reproduction angular error for evaluating the performance of illuminant estimation algorithms

The angle between the RGBs of the measured illuminant and estimated illuminant colors - the recovery angular error - has been used to evaluate the performance of the illuminant estimation algorithms. However we noticed that this metric is not in line with how the illuminant estimates are used. Normally, the illuminant estimates are ‘divided out’ from the image to, hopefully, provide image colors that are not confounded by the color of the light. However, even though the same reproduction results the same scene might have a large range of recovery errors. In this work the scale of the problem with the recovery error is quantified. Next we propose a new metric for evaluating illuminant estimation algorithms, called the reproduction angular error, which is defined as the angle between the RGB of a white surface when the actual and estimated illuminations are ‘divided out’. Our new metric ties algorithm performance to how the illuminant estimates are used. For a given algorithm, adopting the new reproduction angular error leads to different optimal parameters. Further the ranked list of best to worst algorithms changes when the reproduction angular is used. The importance of using an appropriate performance metric is established.