ZM_FAST_IMAGE_BLENDS
To detect alarms ZoneMinder needs to blend the captured image with the stored reference image to update it for comparison with the next image. The reference blend percentage specified for the monitor controls how much the new image affects the reference image. There are two methods that are available for this. If this option is set then fast calculation which does not use any multiplication or division is used. This calculation is extremely fast, however it limits the possible blend percentages to 50%, 25%, 12.5%, 6.25%, 3.25% and 1.5%. Any other blend percentage will be rounded to the nearest possible one. The alternative is to switch this option off and use standard blending instead, which is slower.