1. An image processing apparatus including an image processing circuit, said image processing circuit comprising: an intermediate image generating unit configured to generate a first horizontal intermediate image by extracting a horizontal component in a particular frequency band in an input image and a first vertical intermediate image by extracting a vertical component in a particular frequency band in the input image; an intermediate image processing unit configured to generate a second intermediate image from the first horizontal intermediate image and the first vertical intermediate image; and a first adding unit configured to add the input image and the second intermediate image; wherein the intermediate image processing unit comprises: a horizontal zero-crossing point decision unit configured to identify a point where the pixel value in the first horizontal intermediate image changes from positive to negative or from negative to positive as a zero-crossing point; and a horizontal signal amplifying unit that generates a horizontal non-linearly processed image by amplifying the pixel value of each pixel in the vicinity of the zero-crossing point, among the pixels forming the first horizontal intermediate image, by an amplification factor greater than 1; a horizontal high-frequency component image generating unit configured to generate a second horizontal intermediate image by extracting only a high-frequency component in the horizontal non-linearly processed image; a vertical zero-crossing point decision unit configured to identify a point where the pixel value in the first vertical intermediate image changes from positive to negative or from negative to positive as a zero-crossing point; a vertical signal amplifying unit that generates a vertical non-linearly processed image by amplifying the pixel value of each pixel in the vicinity of the zero-crossing point, among the pixels forming the first vertical intermediate image, by an amplification factor greater than 1; a vertical high-frequency component image generating unit configured to generate a second vertical intermediate image by extracting only a high-frequency component in the vertical non-linearly processed image; and a second adding unit configured to add the first horizontal intermediate image, the first vertical intermediate image, the second horizontal intermediate image, and the second vertical intermediate image, and to output a resulting sum as the second intermediate image; and wherein the second adding unit comprises at least one of a first horizontal-vertical combining unit configured to take a weighted sum of the first horizontal intermediate image and the first vertical intermediate image, and a second horizontal-vertical combining unit configured to take a weighted sum of the second horizontal intermediate image and the second vertical intermediate image.