1. An apparatus for reducing noise from an image sensor, the apparatus comprising: a noise-estimation unit which estimates a noise level representing an image frame expressed as a component in a color space; an impulse-detection unit detecting at least one pixel corresponding to an impulse pixel among pixels constituting the image frame using the estimated noise level; a filter-strength-calculation unit which determines filter strength based on whether a current pixel is the impulse pixel; and a filter-application unit which filters the pixels constituting the image frame according to the determined filter strength, wherein the first impulse-detection unit determines if a difference between a current luma pixel value and a mean pixel value within a boundary block of a size is greater than an impulse threshold value T impulse , counts a number of cases where a difference between the current luma pixel and an adjacent pixel within the boundary block is less than a threshold value T var if the difference between the current luma pixel value and the mean pixel value is greater than the impulse threshold value T impulse , and then determines the current luma pixel as an impulse pixel if the number is less than a given number.