Recent digital camera development tendency shows the higher ISO extension which enables a user to take a picture in deemed lighting condition without using a flash or another equipment. Also noise reduction function has been developed to adjust the higher ISO extension. But using the high ISO causes a lot of noises so that proper noise reduction function should be adjusted. So the manufacturers introduce the advanced noise reduction function with higher ISOs as the digital camera performance development. On the other hands, the defect of noise reduction is not widely open such as remaining noise in high ISOs and decreasing resolution. Therefore, in this research we verify and experiment the decrease of resolution by using noise reduction function on a digital camera. Moreover we analyze the results how much the noise reduction function effects to the image resolution. And we present the results as practical numerical values.