An image sensor and method thereof. In an example, the image sensor, may include a pixel array including a plurality of unit pixels, each of the plurality of unit pixels having a charge transfer unit for transferring charges accumulated in an optoelectronic converter to a charge detector via a charge transfer driving signal. The example image sensor may further include a row driving unit generating a boosted voltage, the boosted voltage set to a boosted voltage level higher than a power voltage level, the boosted voltage selectively boosted in response to a boosting voltage variable control signal. The row driving unit may selectively apply the charge transfer driving signal to the pixel array. In another example, the method may include selectively adjusting a voltage level of a charge transfer driving voltage and transferring the charge transfer driving voltage to a charge transfer unit for controlling an operation of the charge transfer unit.