An image sensor may include an array of photodiodes and readout circuitry. A group of adjacent photodiodes in the array may be covered with a first color filter element that transmits a first color light and an additional group of adjacent photodiodes may be covered with a second color filter element that transmits a second color light. The group of photodiodes may share a floating diffusion node. The array may be operable in a low resolution mode in which the readout circuitry reads out image signals corresponding to a sum of charges generated by the group of photodiodes and in a high resolution mode in which the readout circuitry reads out image signals corresponding to charges generated by each of the photodiodes from the shared floating diffusion node. The photodiodes in the group may capture charge using different integration times for generating high-dynamic-range images.