Effective megapixels
From The Glossary of Digital Photography
Not all pixels end up in the image produced by the camera. Some of the pixels are used for other purposes. For example, pixels along the edges of an image are often masked out or used to determine black or complete darkness needed to compute image light levels. Effective megapixel refers to the actual number of pixels in the final image plus the ring pixels. Thus there will be slightly more effective megapixels than the megapixel count in the final image. See also pixel; megapixel; ring pixel
