获取exr图片上像素点的颜色通道

google了好久，都没找到合适的方法，还是自己撸一串吧。

import OpenEXR, Imath, array

def get_channel(exr_file,pixel_pos,channel='R'):
    # Open the input file
    file = OpenEXR.InputFile(exr_file)
    f_header=file.header()
    dw = f_header['dataWindow']

    #get pixel pos relative to the datawidnow
    pixel_data_pos=(pixel_pos[0]-dw.min.x, pixel_pos[1]-dw.min.y)
    #convert 2d array to 1d array index
    pixel_index=pixel_data_pos[1]*(dw.max.x-dw.min.x+1)+pixel_data_pos[0]-1

    # Read the specified channle color as 32-bit floats
    float_type = Imath.PixelType(Imath.PixelType.FLOAT)
    return array.array('f', file.channel(channel, float_type)).tolist()[pixel_index]
#examples
get_channel('*.exr',(0,0))