In a method of operating an image sensor, a first pixel and a second pixel are commonly connected to a floating diffusion node. A voltage of the floating diffusion node is boosted. A first image signal of the first pixel is read through the floating diffusion node after of the voltage of the floating diffusion node is boosted. A second image signal of the second pixel is read through the floating diffusion node after the first image signal is read. The image sensor has a shared structure in which a plurality of pixels are connected to a single floating diffusion node. Blooming may be reduced in the image sensor by boosting the voltage of the floating diffusion node before reading the image signal to lower the potential barrier formed between the photodiode and the floating diffusion node and drain the saturated photocharges into the floating diffusion node.