ESA Science & Technology - INTEGRAL: SPI coded-mask instrument

Artist's impression of INTEGRAL highlighting SPI, one of the coded-mask instruments onboard the spacecraft (left).  A sketch demonstrating how the coded-mask camera works shows gamma-rays from two different astronomical sources passing through the mask's holes (right). Some of the incident gamma-rays can pass through the mask and illuminate pixels on the detector below (shown in blue and red, respectively), while others are blocked by the mask's opaque spots, casting shadows on the detector (shown in white).