Disclosed are an image processing apparatus which effectively corrects, by a simple method, color crosstalk that is generated in a captured image by light obliquely entering an image sensor, and a control method thereof. A white-detection area used in white balance processing for a captured image signal is set in accordance with an aperture value used in image capturing. The degree of color crosstalk depends on an aperture value used in image capturing, and the spectral sensitivity characteristic of the image sensor changes depending on the degree of color crosstalk. By setting a white-detection range to correct a change of the spectral sensitivity characteristic depending on the aperture value, color crosstalk can be simply, effectively corrected.