An image sensor capable of global shutter operation and including an array of pixels, each of the pixels comprising: a photo-sensitive element for generating charges in response to incident radiation, wherein the photosensitive element is a pinned photo diode; a sense node; a transfer gate, connected between the photo-sensitive element and the sense node, for controlling transfer of charges to the sense node; a reset switch connected to the sense node for resetting the sense node to a predetermined voltage; a first buffer amplifier (AMP1, M2) having an input connected to the sense node; a sample stage comprising a sample switch connected to an output of the first buffer amplifier (AMP1, M2), which is operable to sample a value of the sense node, and a storage element for storing a signal level sampled by the sample switch; and, a second buffer amplifier (AMP2, M4) having an input connected to the sample stage; and, said pixel array further comprising control circuitry which is arranged to: reset the sense node; cause the sample stage to store a signal sampled on the sense node which represents a reset level of the pixel; operate the transfer gate to transfer charge from the photo-sensitive element to the sense node following exposure to radiation, which transferred charge represents an exposure level of the pixel; read the sampled reset level of the pixel; cause the sample stage to store a signal sampled on the sense node which represents an exposure level of the pixel; and, read the sampled exposure level of the pixel. a photo-sensitive element for generating charges in response to incident radiation, wherein the photosensitive element is a pinned photo diode; a sense node; a transfer gate, connected between the photo-sensitive element and the sense node, for controlling transfer of charges to the sense node; a reset switch connected to the sense node for resetting the sense node to a predetermined voltage; a first buffer amplifier (AMP1, M2) having an input connected to the sense node; a sample stage comprising a sample switch connected to an output of the first buffer amplifier (AMP1, M2), which is operable to sample a value of the sense node, and a storage element for storing a signal level sampled by the sample switch; and, a second buffer amplifier (AMP2, M4) having an input connected to the sample stage; and, said pixel array further comprising control circuitry which is arranged to: reset the sense node; cause the sample stage to store a signal sampled on the sense node which represents a reset level of the pixel; operate the transfer gate to transfer charge from the photo-sensitive element to the sense node following exposure to radiation, which transferred charge represents an exposure level of the pixel; read the sampled reset level of the pixel; cause the sample stage to store a signal sampled on the sense node which represents an exposure level of the pixel; and, read the sampled exposure level of the pixel. reset the sense node; cause the sample stage to store a signal sampled on the sense node which represents a reset level of the pixel; operate the transfer gate to transfer charge from the photo-sensitive element to the sense node following exposure to radiation, which transferred charge represents an exposure level of the pixel; read the sampled reset level of the pixel; cause the sample stage to store a signal sampled on the sense node which represents an exposure level of the pixel; and, read the sampled exposure level of the pixel.