An image sensor is provided. The image sensor includes a pixel array having active pixel sensors arranged in rows and columns; a correlated double sampler that converts sensing signals transferred from pixels sensors selected from the active pixel sensors to correlated double sampling signals and outputs a conversion result by column; and an analog-to-digital converter that converts the correlated double sampling signals corresponding to plural columns to digital signals using a global code. The analog-to-digital converter includes a column shared operator that performs a digital conversion operation on correlated double sampling signals corresponding to two or more columns of the plural columns.