An image processing apparatus and a method thereof are provided. A plurality of target blur radii are obtained by calculating blur radiuses corresponding to the out of focus transform function between a deblurred datum color channel image and the other color channel images. A plurality of deblurred color channel images are obtained by respectively performing deblurring operations on the original channel images according to the target blur radii that are corresponding to the original channel images. The deblurred datum color channel image and the deblurred color channel images are combined to obtain a blur calibrated image. Accordingly, the image out of focus problem induced by dispersion can be solved.