Image processing device, image processing method, and non-transitory computer-readable recording medium for recording image processing program

1. An image processing device comprising:

a white balance correcting section multiplying each color component of image data by a white balance gain for the color component to perform white balance correction;

a color difference calculating section calculating color difference components of the image data after the white balance correction, for each pixel;

a color difference correcting section performing color difference correction processing for reducing the color difference components for a processing target pixel when all the color difference components of the processing target pixel are within a predetermined color difference correction range;

a color difference correction range setting section setting the color difference correction range wider as the white balance gain is larger and narrower as the white balance gain is smaller; and

a bit precision converting section converting bit precision of the image data to bits-to-be-processed precision of the color difference correcting section at a stage preceding the color difference correcting section.

2. The image processing device according to claim 1 , wherein

the color difference correction range setting section further sets the color difference correction range wide according to an expansion ratio if bit precision conversion by the bit precision converting section is precision expansion and sets the color difference correction range narrow according to a reduction ratio if the bit precision conversion is precision reduction.

3. The image processing device according to claim 2 , wherein the color difference correction range setting section sets the color difference correction range to (Bpro/B0) times, where B0 denotes the bit precision of the image data and Bpro denotes the bits-to-be-processed precision of the color difference correcting section.

4. The image processing device according to claim 3 , wherein

the white balance correcting section multiplies RGB components of the image data by white balance gains WGr, WGg and WGb for the RGB components, respectively, to perform white balance correction; and

the color difference correction range setting section sets a color difference correction range for the R component to a magnification ratio corresponding to a ratio of (WGr/WGg) and sets a color difference correction range for the B component to a magnification ratio corresponding to a ratio of (WGb/WGg).

5. The image processing device according to claim 1 , wherein the color difference correcting section performs the color difference correction processing if a value of a luminance component of the processing target pixel is within a predetermined luminance range.

6. The image processing device according to claim 5 , wherein

the predetermined luminance range is set in plurality in a manner that the predetermined luminance ranges do not overlap with one another;

the color difference correction range is specified for each of the plural predetermined luminance ranges in advance; and

if the value of the luminance component of the processing target pixel is included in any one of the plural predetermined luminance ranges, the color difference correction range setting section sets the color difference correction range for the luminance range in which the value of the luminance component of the processing target pixel is included.

7. The image processing device according to claim 1 , wherein the color difference correction processing by the color difference correcting section is performed at a stage prior to any nonlinear image processing performed for the image data.

8. An image processing method comprising:

a white balance correcting step of multiplying each color component of image data by a white balance gain for the color component to perform white balance correction;

a bit precision converting step of converting bit precision of the image data after the white balance correcting step to bits-to-be-processed precision of a color difference correcting step;

the color difference calculating step of calculating color difference components of the image data, for each pixel;

a color difference correction step of performing color difference correction processing for reducing the color difference components for a processing target pixel when all the color difference components of the processing target pixel are within a predetermined color difference correction range; and

a color difference correction range setting step of setting the color difference correction range wider as the white balance gain is larger and narrower as the white balance gain is smaller.

9. A non-transitory computer-readable recording medium recording an image processing program, the image processing program including:

a white balance correcting step of multiplying each color component of image data by a white balance gain for the color component to perform white balance correction;

a bit precision converting step of converting bit precision of the image data after the white balance correcting step to bits-to-be-processed precision of a color difference correcting step;

the color difference calculating step of calculating color difference components of the image data, for each pixel;

a color difference correction step of performing color difference correction processing for reducing the color difference components for a processing target pixel when all the color difference components of the processing target pixel are within a predetermined color difference correction range; and

a color difference correction range setting step of setting the color difference correction range wider as the white balance gain is larger and narrower as the white balance gain is smaller.