1. Field of the Invention
The present general inventive concept relates to an apparatus to measure noise in an image signal and a method thereof, and more particularly, to an apparatus to measure an amount of noise in an image signal, usable with a process of attenuating the noise in the image signal, and a method thereof.
2. Description of the Related Art
Noise added to an image signal is the main cause of deterioration of image quality and lowering of performance of encoding and decoding of the image signal. Accordingly, many techniques for improving the image quality and the performance of encoding and decoding of the image signal by attenuating noise added to the image signal have been developed. In order to attenuate the noise added to the image signal, an amount of noise added to the image signal should first be measured accurately. For this, apparatuses for measuring noise in an image signal have been used. The amount of noise measured by the noise measurement apparatuses is generally expressed by a variance value or standard deviation that is the square root of the variance value.
FIG. 1 is a block diagram illustrating a conventional apparatus for measuring noise in an image signal. Referring to FIG. 1, the conventional apparatus for measuring the noise in the image signal includes a SAD (Sum of Absolute Difference) calculation unit 10, a SAD comparison unit 20, a SAD counter 30, a comparison unit 40 and a variation counter 50.
The SAD calculation unit 10 calculates the sum of absolute difference (SAD) values among adjacent pixels of an input image. The SAD comparison unit 20 compares the calculated SAD value and detects whether each SAD value calculated by the SAD calculation unit 10 belongs to a predetermined range as a result of the comparison. The SAD comparison unit 20 outputs a true value if the calculated SAD value belongs to the predetermined range and outputs a false value if the calculated SAD value does not belong to the predetermined range. A counted value of the SAD counter 30 is increased if the output of the SAD comparison unit 20 is the true value. The SAD counter 30 is reset for a period of a picture (i.e., field or frame). Accordingly, the SAD counter 30 counts the SAD values that belong to the predetermined range for each picture.
The comparison unit 40 compares the value of the SAD counter 30 with a predetermined value. If the output value of the SAD counter 30 is less than the predetermined value, the comparison unit 40 makes the variation counter 50 perform an up-counting, while if the output value of the SAD counter 30 is greater than the predetermined value, the comparison unit 40 makes the variation counter 50 perform a down-counting, for the period of a picture. The output value of the variation counter 50, which is increased and decreased according to the comparison unit 40, becomes a noise measurement value, and this noise measurement value is fed back to the SAD comparison unit 20 to be referred to in determining the predetermined range.
However, the conventional apparatus for measuring noise in the image signal as described above has the drawbacks in that the noise measurement value is calculated according to the SAD distribution of the image signal, and thus the noise measurement value may be differently calculated according to the characteristics of the image signals irrespective of the amount of noise applied to the image signals.
For example, even if the amount of noise applied to an image that is complicated or has many minute parts is the same as that applied to an image that is simple or has many flat parts, the noise measurement value may differently be calculated according to the SAD value distribution. Accordingly, it is necessary to calculate an accurate noise measurement value irrespective of the characteristics of the image signal.