Apparatus and method for reducing image noise
A spatial noise reducing section 20 calculates a spatial NR pixel value Snr by reducing spatial noise from an input pixel value Pin. A temporal noise reducing section 30 calculates a temporal NR pixel value Tnr by reducing temporal noise from the input pixel value Pin. A temporal noise reduction result determining section 50 compares the magnitude of the pixel values among the input pixel value Pin, the spatial NR pixel value Snr, and the temporal NR pixel value Tnr, and outputs, based on the comparison result, one of the pixel values as a noise reduction result (an output pixel value Pout). Thus, it is made possible to perform strong temporal noise reduction on a moving image while preventing generation of residual images in a motion image area.
1. An apparatus for reducing image noise which reduces noise in an image, the apparatus comprising:
a spatial noise reducing section that reduces noise from an input image by smoothing a pixel value in a spatial direction within a current image frame;
a temporal noise reducing section that reduces noise from the input image by smoothing the pixel value in a temporal direction between the current image frame and a temporally preceding image frame;
a pixel value range setting section that sets a pixel value range based on the pixel value of the input image and a pixel value of an image outputted by the spatial noise reducing section; and
a range determining section that outputs: a pixel value of an image outputted by the temporal noise reducing section when the pixel value of the image outputted by the temporal noise reducing section is within the pixel value range; a maximum value of the pixel value range when the pixel value of the image outputted by the temporal noise reducing section is greater than the maximum value; and a minimum value of the pixel value range when the pixel value of the image outputted by the temporal noise reducing section is less than the minimum value.
2. The apparatus for reducing image noise according to claim 1 , wherein
the pixel value range setting section includes:
a difference value calculating section that calculates a difference value between the pixel value of the input image and the pixel value of the image outputted by the spatial noise reducing section;
a margin setting section that obtains two margin values by multiplying a predetermined margin rate for spatial noise reduction and a predetermined margin rate for an input image each by the difference value; and
an adding section that, based on a sign of the difference value, adds one of the two margin values to the pixel value of the input image to obtain the maximum value of the pixel value range, and adds the other of the two margin values to the pixel value of the input image to obtain the minimum value of the pixel value range.
3. The apparatus for reducing image noise according to claim 1 , wherein
the pixel value range setting section includes:
a selecting section that compares the pixel value of the input image and the pixel value of the image outputted by the spatial noise reducing section to select the maximum value and the minimum value of the pixel value range;
a margin setting section in which a margin value is predetermined; and
an adding section that adds the predetermined margin value to each of the maximum value and the minimum value of the pixel value range.
4. The apparatus for reducing image noise according to claim 3 , wherein:
the pixel value range setting section further includes a difference absolute value calculating section that calculates the absolute value of the difference between the pixel value of the input image and the pixel value of the image outputted by the spatial noise reducing section; and
the margin setting section provides the adding section with a margin value obtained by multiplying the predetermined margin value by the absolute value of the difference.
5. A method for reducing image noise which reduces noise in an image, the method comprising:
a spatial noise reducing step of reducing noise from an input image by smoothing a pixel value in a spatial direction within a current image frame;
a temporal noise reducing step of reducing noise from the input image by smoothing the pixel value in a temporal direction between the current image frame and a temporally preceding image frame;
a range setting step of setting a pixel value range based on the pixel value of the input image and a pixel value of an image outputted in the spatial noise reducing step; and
a range determining step of outputting: a pixel value of an image outputted in the temporal noise reducing step when the pixel value of the image outputted in the temporal noise reducing step is within the pixel value range; a maximum value of the pixel value range when the pixel value of the image outputted in the temporal noise reducing step is greater than the maximum value; and a minimum value of the pixel value range when the pixel value of the image outputted in the temporal noise reducing step is less than the minimum value.
6. The method for reducing image noise according to claim 5 , wherein
the range setting step includes:
a difference value calculating step of calculating a difference value between the pixel value of the input image and the pixel value of the image outputted in the spatial noise reducing step;
a margin setting step of obtaining two margin values by multiplying a predetermined margin rate for spatial noise reduction and a predetermined margin rate for an input image each by the difference value; and
an adding step of, based on a sign of the difference value, adding one of the two margin values to the pixel value of the input image to obtain the maximum value of the pixel value range, and adding the other of the two margin values to the pixel value of the input image to obtain the minimum value of the pixel value range.
7. An integrated circuit used for an apparatus for reducing image noise which reduces noise in an image, the integrated circuit comprising circuitry functioning as:
a spatial noise reducing section that reduces noise from an input image by smoothing a pixel value in a spatial direction within a current image frame;
a temporal noise reducing section that reduces noise from the input image by smoothing the pixel value in a temporal direction between the current image frame and a temporally preceding image frame;
a pixel value range setting section that sets a pixel value range based on the pixel value of the input image and a pixel value of an image outputted by the spatial noise reducing section; and
a range determining section that outputs: a pixel value of an image outputted by the temporal noise reducing section when the pixel value of the image outputted by the temporal noise reducing section is within the pixel value range; a maximum value of the pixel value range when the pixel value of the image outputted by the temporal noise reducing section is greater than the maximum value; and a minimum value of the pixel value range when the pixel value of the image outputted by the temporal noise reducing section is less than the minimum value.