Disclosed is an image processing apparatus and a control method thereof that can correct the brightness of a pixel in an image. Reflection characteristics of environment light when the image is captured are estimated by applying smoothing to the image. The brightness of the pixel is corrected by computing a correction value for correcting the brightness of the pixel based on the reflection characteristics of the environment light and adding the correction value to the pixel. The brightness can be corrected while suppressing an amplification of noise and a loss of details of a subject.