An image sensor includes a pixel array where each pixel is formed in a portion of a substrate electrically insulated from other portions of the substrate. Each pixel includes a photodetector; a transfer transistor; and a readout circuit comprising one or a plurality of transistors. The transistors of the readout circuit are formed inside and on top of at least one well of the portion. The reading from the photodetector of a pixel of a current row uses at least one transistor of the readout circuit of a pixel of at least one previous row, the well of the pixel of the previous row being biased with a first voltage greater than a second bias voltage of the well of the pixel of the current row.