Method of adjusting output level of measurement pixel, colour sensor and virtual slide apparatus is related. The method of adjusting an output level of a measurement pixel may include a first step of selecting a type of a target sample from a plurality of previously determined sample type candidates, a second step of measuring an output level of a reference pixel based on light from the target sample incident on the reference pixel, a third step of selecting a level adjustment parameter associated with the type of the target sample selected in the first step, the plurality of candidates being associated with the type of the target sample, a fourth step of calculating a level adjustment amount of the measurement pixel, and a fifth step of adjusting the output level using the level adjustment amount when measuring an output level corresponding to the light from the target sample.