功能：光度立体法主要应用于物体表面瑕疵检测以及三维重建。本文主要讲述它在表面检测领域的应用。

对于物体表面的微小瑕疵，从不同角度打光，成像效果自然有好有坏。光度立体法基于多种角度打光的图像，计算图像的梯度

  1. 初始化

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    dev_close_window ()
    dev_update_off ()
    dev_open_window (0, 0, 640, 512, 'black', WindowHandle)
    set_display_font (WindowHandle, 14, 'mono', 'true', 'false')
    Message := 'Inspect the label of flooring panels'
    Message[1] := 'using photometric stereo. In this case four'
    Message[2] := 'different light orientations were used.'
    disp_message (WindowHandle, Message, 'window', 12, 12, 'black', 'true')
    disp_continue_message (WindowHandle, 'black', 'true')
    stop ()

  2. 使用光度立体法得到曲率图，检测缺陷

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    for Index := 1 to 2 by 1
        * 不同角度打光的图像
        read_image (Images, 'photometric_stereo/flooring_' + Index + '_0' + [1:4])
        for I := 1 to 4 by 1
            Message := 'Acquire image ' + I + ' of 4'
            select_obj (Images, ObjectSelected, I)
            dev_display (ObjectSelected)
            disp_message (WindowHandle, Message, 'window', 12, 12, 'black', 'true')
            wait_seconds (0.5)
        endfor
        
        * 光照倾斜角度和光照旋转角度
        Slants := [39.4, 40.5, 39.5, 38.4]
        Tilts := [-6.0, 83.7, 172.9, -98.2]
        * 计算结果，表面梯度和反照率
        ResultType := ['gradient', 'albedo']
        * 光度立体法
        photometric_stereo (Images, HeightField, Gradient, Albedo, Slants, Tilts, ResultType, 'poisson', [], [])
       
        dev_display (Albedo)
        disp_message (WindowHandle, 'Albedo image', 'window', 12, 12, 'black', 'true')
        disp_continue_message (WindowHandle, 'black', 'true')
        stop ()
        
        * 计算表面的高斯曲率，输入为梯度场，输出为均值曲率图像。
        derivate_vector_field (Gradient, MeanCurvature, 1.0, 'mean_curvature')
        
        * 在均值曲率图像上检测缺陷
        threshold (MeanCurvature, Region, 0.02, 1000)
        connection (Region, Defects)
        area_center (Defects, Area, Row, Column)
        gen_circle (Circle, Row, Column, sqrt(Area) + 10)
        
        dev_set_draw ('margin')
        dev_set_color ('red')
        dev_set_line_width (2)
        dev_display (MeanCurvature)
        dev_display (Circle)
        Message := 'The defects can easily be detected'
        Message[1] := 'in the surface curvature image'
        disp_message (WindowHandle, Message, 'window', 12, 12, 'black', 'true')
        stop ()
        
        dev_set_draw ('margin')
        dev_set_color ('red')
        dev_display (Albedo)
        dev_display (Circle)
        disp_message (WindowHandle, 'Defects in albedo image', 'window', 12, 12, 'black', 'true')
        if (Index < 2)
            disp_continue_message (WindowHandle, 'black', 'true')
            stop ()
        endif
    endfor