An image processing device comprising: a storage unit configured to store a look-up table L1 where an input gradation value and a brightness value are associated with each other in a manner satisfying the GSDF curve defined by the DICOM standard and a look-up table L2 where an input gradation value and a brightness value are associated with each other in a manner satisfying a gamma curve where a gamma value is a value from 1.8 to 2.6 or a function according to Rec.709, perceptual quantization PQ or Hybrid Log Gamma HLG standards, a saturation value acquisition unit configured to acquire a saturation value of each pixel included in input image data input into the image processing device a mixing unit configured to determine a predetermined mixing ratio W for each pixel based on the acquired saturation value of the pixel, a monochrome correction unit configured to acquire a brightness value corresponding to an input gradation value of the pixel by referring to the look-up table L1, and output a first brightness value obtained by multiplying the acquired brightness value by a coefficient obtained by subtracting the predetermined mixing ratio W from the value one, a colour correction unit configured to acquire a brightness value corresponding to an input gradation value of the pixel by referring the look-up table L2, and output a second brightness value obtained by multiplying the acquired brightness value by the predetermined mixing ratio W, and a correction unit configured to determine a sum of the first brightness value and the second brightness value wherein the predetermined mixing ratio W is such that W <= g(c) for saturation values below a first threshold value, wherein the function g(c) increases proportionally from the minimum value 0 to the maximum value 1 as the saturation value c increases from the minimum saturation value to the maximum saturation value, and such that W = f(c) for saturation values equal to or greater than the first threshold value, wherein, for each saturation value c, f(c)>αg(c) with α>=1. a storage unit configured to store a look-up table L1 where an input gradation value and a brightness value are associated with each other in a manner satisfying the GSDF curve defined by the DICOM standard and a look-up table L2 where an input gradation value and a brightness value are associated with each other in a manner satisfying a gamma curve where a gamma value is a value from 1.8 to 2.6 or a function according to Rec.709, perceptual quantization PQ or Hybrid Log Gamma HLG standards, a saturation value acquisition unit configured to acquire a saturation value of each pixel included in input image data input into the image processing device a mixing unit configured to determine a predetermined mixing ratio W for each pixel based on the acquired saturation value of the pixel, a monochrome correction unit configured to acquire a brightness value corresponding to an input gradation value of the pixel by referring to the look-up table L1, and output a first brightness value obtained by multiplying the acquired brightness value by a coefficient obtained by subtracting the predetermined mixing ratio W from the value one, a colour correction unit configured to acquire a brightness value corresponding to an input gradation value of the pixel by referring the look-up table L2, and output a second brightness value obtained by multiplying the acquired brightness value by the predetermined mixing ratio W, and a correction unit configured to determine a sum of the first brightness value and the second brightness value wherein the predetermined mixing ratio W is such that W <= g(c) for saturation values below a first threshold value, wherein the function g(c) increases proportionally from the minimum value 0 to the maximum value 1 as the saturation value c increases from the minimum saturation value to the maximum saturation value, and such that W = f(c) for saturation values equal to or greater than the first threshold value, wherein, for each saturation value c, f(c)>αg(c) with α>=1.