an image sensor configured to acquire an image;

an image processor configured to generate a quantized image by selecting one of a plurality of preset reference values based on whether a pixel value of the acquired image is less than a threshold value of a trained quantization filter, determining a difference between the pixel value of the acquired image and the selected reference value, and adjusting one or more of pixel values of the acquired image based on the difference; and

an output interface configured to output the quantized image,

wherein the preset reference values are determined based on the threshold value and a range of pixel values of the acquired image.