Image sensor and image capturing apparatus

An image sensor, comprises: a pixel area that includes first and second pixel groups each constituted by a plurality of pixels; first and second output channels that output image signals obtained from the first and second pixel groups, respectively; and a driver that performs drive according to a first drive method in which the first pixel group is alternately exposed in a medium exposure period and a short exposure period in a first cycle so that a first and second image signals are read out, and in which the second pixel group is exposed in a long exposure period in a second cycle longer than the first cycle so that a third image signal is read out. The reading out of the third image signal and reading out of the first or the second image signal are performed in parallel.