1. An image processing apparatus comprising: a conversion means for generating a tone-converted image by converting luminance L 1 of pixels comprising a first input image based on a conversion function; a reduced image generation means for generating a reduced image from the tone-converted image; a smoothing means for generating a smoothed image having luminance L c of pixels comprising the first input image based on an interpolation calculation using pixels comprising the reduced image; and a grayscale conversion means for generating a contrast-corrected image based on luminance L c of pixels comprising the first input image, luminance L 1 of pixels comprising the smoothed image, and a predetermined gain value g, wherein gain value g is determined by an inverse number of a gradient of a tone curve.