Noise reduction circuit
A noise reduction circuit comprises correlation value calculation means for calculating correlation values in a plurality of directions centered at a pixel to be corrected; correction amount calculation means for calculating, on the basis of the correlation values in the plurality of directions calculated by the correlation value calculation means, a correction amount corresponding to the pixel to be corrected for each of the directions; first correction value calculation means for producing a plurality of candidates for correction values corresponding to the pixel to be corrected on the basis of the correction amount for each of the directions which is calculated by the correction amount calculation means; and second correction value calculation means for calculating the correction value for the pixel to be corrected from the plurality of candidates for correction values corresponding to the pixel to be corrected which are produced by the first correction value calculation means.
1. A noise reduction circuit comprising:
correlation value calculation means for calculating correlation values in a plurality of directions centered at a pixel to be corrected;
correction amount calculation means for calculating, on the basis of the correlation values in the plurality of directions calculated by the correlation value calculation means, a correction amount corresponding to the pixel to be corrected for each of the directions;
first correction value calculation means for producing a plurality of candidates for correction values corresponding to the pixel to be corrected on the basis of the correction amount for each of the directions which is calculated by the correction amount calculation means; and
second correction value calculation means for calculating the correction value for the pixel to be corrected from the plurality of candidates for correction values corresponding to the pixel to be corrected which are produced by the first correction value calculation means.
2. The noise reduction circuit according to claim 1 , wherein
in a case where the number of directions in which correlation is strong is two or more, the correction amount calculation means calculates, in the direction in which correlation is strong, the correction amount corresponding to the pixel to be corrected such that the correction value for the pixel to be corrected is equal to the average of the pixel values of two pixels with the pixel to be corrected interposed therebetween in the direction, while calculating, in the direction in which correlation is weak, the correction amount such that the correction value for the pixel to be corrected is closer to the pixel value of the pixel to be corrected than the average of the pixel values of the two pixels with the pixel to be corrected interposed therebetween in the direction, and
in a case where the number of directions in which correlation is strong is only one, the correction amount calculation means calculates, in the direction in which correlation is strong, the correction amount corresponding to the pixel to be corrected such that the correction value for the pixel to be corrected is equal to the average of the pixel values of two pixels with the pixel to be corrected interposed therebetween in the direction, and giving, in the direction in which correlation is weak, a correction amount which is as identical as possible to the correction amount calculated in the direction in which correlation is strong.
3. The noise reduction circuit according to claim 1 , wherein
the second correction value calculation means calculates the average of the plurality of candidates for correction values corresponding to the pixel to be corrected which are produced by the first correction value calculation means, to calculate a correction value for the pixel to be corrected.
4. The noise reduction circuit according to claim 1 , further comprising
movement amount calculation means for calculating the movement amount of the pixel to be corrected on the basis of the pixel value of the pixel to be corrected and a correction value for the same pixel position as that in the preceding frame, and
control means for controlling the characteristics of the correction amount calculation means on the basis of the movement amount calculated by the movement amount calculation means,
the control means controlling the characteristics of the correction amount calculation means such that the correction amount calculated by the correction amount calculation means is increased depending on the movement amount when the movement amount is within a relatively small range.
5. The noise reduction circuit according to claim 1 , further comprising
third correction value calculation means for calculating a final correction value for the pixel to be corrected,
the third correction value calculation means calculating the final correction value for the pixel to be corrected on the basis of the correction value for the pixel to be corrected calculated by the second correction value calculation means, the pixel value of the pixel to be corrected, and a final correction value calculated by the third correction value calculation means in the preceding frame for a pixel at the same position as the pixel to be corrected.
6. A noise reduction circuit comprising:
correlation value calculation means for calculating correlation values in a plurality of directions centered at
a pixel to be corrected;
correction amount calculation means for calculating, on the basis of the correlation values in the plurality of directions calculated by the correlation value calculation means, a correction amount corresponding to the pixel to be corrected for each of the directions;
correction amount determination means for calculating the average of the correction amounts for the directions calculated by the correction amount calculation means; and
correction value calculation means for calculating a correction value for the pixel to be corrected on the basis of the average of the correction amounts for the directions calculated by the correction amount determination means.
7. The noise reduction circuit according to claim 6 , wherein
in a case where the number of directions in which correlation is strong is two or more, the correction amount calculation means calculates, in the direction in which correlation is strong, the correction amount corresponding to the pixel to be corrected such that the correction value for the pixel to be corrected is equal to the average of the pixel values of two pixels with the pixel to be corrected interposed therebetween in the direction, while calculating, in the direction in which correlation is weak, the correction amount such that the correction value for the pixel to be corrected is closer to the pixel value of the pixel to be corrected than the average of the pixel values of the two pixels with the pixel to be corrected interposed therebetween in the direction, and
in a case where the number of directions in which correlation is strong is only one, the correction amount calculation means calculates, in the direction in which correlation is strong, the correction amount corresponding to the pixel to be corrected such that the correction value for the pixel to be corrected is equal to the average of the pixel values of two pixels with the pixel to be corrected interposed therebetween in the direction, and giving, in the direction in which correlation is weak, a correction amount which is as identical as possible to the correction amount calculated in the direction in which correlation is strong.
8. The noise reduction circuit according to claim 6 , wherein
the correction value calculation means adds the pixel value of the pixel to be corrected to the average of the correction amounts for the directions calculated by the correction amount determination means, to calculate the correction value for the pixel to be corrected.
9. The noise reduction circuit according to claim 6 , further comprising
movement amount calculation means for calculating the movement amount of the pixel to be corrected on the basis of the pixel value of the pixel to be corrected and a correction value for the same pixel position as that in the preceding frame, and
control means for controlling the characteristics of the correction amount calculation means on the basis of the movement amount calculated by the movement amount calculation means,
the control means controlling the characteristics of the correction amount calculation means such that the correction amount calculated by the correction amount calculation means is increased depending on the movement amount when the movement amount is within a relatively small range.
10. The noise reduction circuit according to claim 6 , further comprising
final correction value calculation means for calculating a final correction value for the pixel to be corrected,
the final correction value calculation means calculating the final correction value for the pixel to be corrected on the basis of the correction value for the pixel to be corrected calculated by the correction value calculation means, the pixel value of the pixel to be corrected, and a final correction value calculated by the final correction value calculation means in the preceding frame for a pixel at the same position as the pixel to be corrected.