Plain block matching, and may improved block based matching techniques, fail to determine real physical motion when there is a marked change in luminance. Such changes occur often, but most of the time, the block average changes only a few units per frame, if the frame rate is reasonably high. This is not enough to completely upset plain block matching. When special effects are present, or frame rates are low, the effect becomes more important. Then vectors returned by plain block matching try to match the change in average luminance. What happens as a result of this depends on the exact codec used. Some coders will find the resulting total difference energy too large, and switch to intra mode coding. An example of this behavior is the problem most MPEG encoders have with photographic flashlights. A more intelligent codec might still code in inter mode, but will have to recode all details in the block, because of the wrong vector. If we could use a vector that keeps track of real physical motion and a codec that can deal with DC changes separately, we would be much better off. In this paper we describe a simple way to correct for these illumination changes, without adding any worthwhile computational burden to the encoder and show that the additional to an improved block matching algorithm is able to generate more realistic motion vectors.