1. An imaging sensor, comprising: a pixel array including: an active imaging portion configured to output a first signal corresponding to an amount of light incident on the pixel array, and a first shielded portion comprising a plurality of first shielded regions, the first shielded portion being shielded from light incident on the pixel array and configured to output a second signal; and a black-level adjustment circuit configured to adjust the first signal, comprising: an average value calculator configured to calculate an average signal value for each of the first shielded regions, a region selector configured to select average signal values that are within a predetermined range, and a black-level adjustment value calculator configured to calculate a black-level adjustment value by using average signal values selected by the region selector, wherein the pixel array further includes a second shielded portion that is shielded from light incident on the pixel array and is configured to provide a third signal that is supplied to a noise suppression circuit configured to adjust the first signal, wherein the pixel array further includes a third shielded portion that is shielded from light incident on the pixel array, comprises a plurality of third shielded regions, and is configured to provide a fourth signal, and wherein the average value calculator is further configured to: calculate the average signal value for each third shielded region, calculate a first region average value for the first shielded portion using the average signal values for each of the first shielded regions, and calculate a second region average value for the third shielded portion using the average signal values for each of the third shielded regions; and the region selector is further configured to select average signal values from the first shielded portion when the first region average value is less than the second region average value and to select average signal values from the third shielded portion when the second region average value is less than the first region average value.