Provided is a method of operating an assessment device which communicates with an image sensor and includes an input buffer and a processor, the method including receiving, by the input buffer, raw image data from the image sensor that is configured to capture a test chart, generating, by the processor, conversion image data based on color domain transformation of the raw image data, generating, by the processor, estimation image data by estimating a non-distorted image based on the conversion image data, and assessing, by the processor, color distortion of the image sensor based on the estimation image data and the conversion image data.