Abstract: An image processing apparatus according to an embodiment includes a setting unit that sets an operator including a target pixel in a process target image, a totaling unit that acquires a gradation value of each pixel within the operator, and generates a histogram indicating the number of pixels corresponding to each gradation value from 0 to a natural number N, and a conversion unit that calculates a new gradation value by adding together the number of pixels corresponding to each of the respective gradation values ranging from gradation value 0 to the gradation value of the target pixel, or by subtracting, from gradation value N, the combined number of pixels corresponding to the respective gradation values ranging from the gradation value of the target pixel to gradation value N, and converts the gradation value of the target pixel into the new gradation value.