1. An image sensor, comprising: a pair of butted sensor tiles, each sensor tile comprising: a pixel array comprising a plurality of rows and columns of photosensitive pixels; a respective row driver for driving the respective rows in dependence of a respective timing signal; a read-out unit for reading out selected pixels among said plurality of pixels; a timing controller for generating the timing signals; at least one imaginary row of photosensitive pixels added below the lowest row of pixels or above the highest row of pixels in at least one of the sensor tiles; wherein the rows and the at least one imaginary row on each tile are grouped in first row groups comprising adjacently arranged rows including said at least one imaginary row, wherein a center-to-center distance between adjacent first row groups is equal to a first distance on both sensor tiles, and wherein a center-to-center distance between first row groups that are on different tiles is substantially equal to one or a multiple of said first distance; wherein the image sensor is separately operable in each of the following modes: a full-resolution mode wherein each row of pixels is individually selectable and wherein the read-out unit is configured to read-out the pixels in the selected row; and a shifted binning mode, wherein each row in a first row group is simultaneously selectable and wherein the different first row groups are individually and sequentially selectable, and wherein the read-out unit is configured to compute an average of the read-outs corresponding to the selected pixels that are in different selected rows.