An image processing apparatus includes: a memory; and a processor configured to execute one or more instructions stored in the memory to: determine a scale weight for each pixel of original pixels in an original image based on first attribute-related information set by dividing the original image into an object region and a peripheral region, respectively; determine an additional weight for at least one pixel of the original pixels in the peripheral region, based on the first attribute-related information, and second attribute-related information that is based on an amount of a change between pixel values of adjacent pixels; and obtain a transformed image of which a size is changed from the original image, by applying at least one of the scale weight and the additional weight to corresponding pixels of the original pixels to obtain a pixel value of a transformed pixel in the transformed image.