An image processing device for performing a preprocessing of an image recognition process to an input image, comprising: a generation element for generating a histogram of luminance values of the input image; a determination element for determining a reference value for the luminance values on the basis of the histogram and determining a high luminance pixel, that is, a pixel having a luminance value greater than the reference value; and a conversion element for converting the luminance value of the high luminance pixel into a luminance value lower than or equal to the reference value, wherein the determination element is configured to determine one or more peak ranges of luminance values on the basis of the histogram and to determine the reference value on the basis of an upper limit value of the peak range having a greatest luminance value or having a second greatest luminance value, and wherein the determination element is configured to calculate, for each bin of the histogram, a gravity center luminance value GLi and a difference between said gravity center luminance value GLi and the luminance value Li associated with the respective bin, the determination element being further configured to cluster luminance values into multiple ranges on the basis of said differences, and to determine a range among the multiple ranges to be a peak range if a range width or a sum of a number of pixels in the range is greater than or equal to a threshold, and to exclude the range otherwise, wherein the gravity center luminance value satisfies: GLi=Σ j (Lj×mj)/Σ j (mj) in which, GLi indicates the gravity center luminance value of the luminance values in N pieces surrounding the i-th luminance value, Lj indicates the j-th luminance value, mj indicates the number of pixels of the j-th luminance value in the histogram, Σ is a sum involving j and indicating a range of i-N/2 to i+N/2, and N, j and i are integers. a generation element for generating a histogram of luminance values of the input image; a determination element for determining a reference value for the luminance values on the basis of the histogram and determining a high luminance pixel, that is, a pixel having a luminance value greater than the reference value; and a conversion element for converting the luminance value of the high luminance pixel into a luminance value lower than or equal to the reference value, wherein the determination element is configured to determine one or more peak ranges of luminance values on the basis of the histogram and to determine the reference value on the basis of an upper limit value of the peak range having a greatest luminance value or having a second greatest luminance value, and wherein the determination element is configured to calculate, for each bin of the histogram, a gravity center luminance value GLi and a difference between said gravity center luminance value GLi and the luminance value Li associated with the respective bin, the determination element being further configured to cluster luminance values into multiple ranges on the basis of said differences, and to determine a range among the multiple ranges to be a peak range if a range width or a sum of a number of pixels in the range is greater than or equal to a threshold, and to exclude the range otherwise, wherein the gravity center luminance value satisfies: GLi=Σ j (Lj×mj)/Σ j (mj) in which, GLi indicates the gravity center luminance value of the luminance values in N pieces surrounding the i-th luminance value, Lj indicates the j-th luminance value, mj indicates the number of pixels of the j-th luminance value in the histogram, Σ is a sum involving j and indicating a range of i-N/2 to i+N/2, and N, j and i are integers.