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例程功能

 演示如何使用edges_color，展示只能从彩色图像中提取某些边缘的图像，说明edges_color和edges_image输出之间的差异。

代码如下

dev_update_off ()
read_image (Image, 'olympic_stadium')
get_image_size (Image, Width, Height)
dev_close_window ()
dev_open_window (0, 0, Width, Height, 'black', WindowHandle)
dev_set_part (0, 0, Height - 1, Width - 1)
set_display_font (WindowHandle, 16, 'mono', 'true', 'false')
dev_display (Image)
Message := 'Color image'
disp_message (WindowHandle, Message, 'window', 12, 12, 'black', 'true')
stop ()
* Convert the color image to a gray value image.  Note that there is no contrast
* between the soccer field and the track in the gray value image.
rgb1_to_gray (Image, GrayImage)
dev_display (GrayImage)
Message := 'Gray value image'
disp_message (WindowHandle, Message, 'window', 12, 12, 'black', 'true')
stop ()
* Compute the color edges without non-maximum suppression and hysteresis
* thresholding, i.e., the raw edge amplitude image.  Note that there is a clearly
* visible edge between the soccer field and the track in the color edge image.
edges_color (Image, ImaAmp, ImaDir, 'canny', 1, 'none', -1, -1)
dev_display (ImaAmp)
Message := 'Color edge image'
disp_message (WindowHandle, Message, 'window', 12, 12, 'black', 'true')
stop ()
* Compute the gray value edges without non-maximum suppression and
* hysteresis thresholding, i.e., the raw edge amplitude image.  Note that there is
* no visible edge between the soccer field and the track in the gray value edge
* image.
edges_image (GrayImage, ImaAmpGray, ImaDirGray, 'canny', 1, 'none', -1, -1)
dev_display (ImaAmpGray)
Message := 'Gray value edge image'
disp_message (WindowHandle, Message, 'window', 12, 12, 'black', 'true')
stop ()
* Now perform the color edge extraction including non-maximum suppression
* and hysteresis thresholding.  Note the segmented edge between the soccer
* field and the track.
edges_color (Image, ImaAmpHyst, ImaDirHyst, 'canny', 1, 'nms', 20, 40)
threshold (ImaAmpHyst, RegionColor, 1, 255)
skeleton (RegionColor, EdgesColor)
dev_display (Image)
dev_set_color ('blue')
dev_display (EdgesColor)
Message := 'Segmented color edges'
disp_message (WindowHandle, Message, 'window', 12, 12, 'black', 'true')
stop ()
* Now perform the gray value edge extraction including non-maximum
* suppression and hysteresis thresholding.  Note the absence of an edge
* between the soccer field and the track.
edges_image (GrayImage, ImaAmpGrayHyst, ImaDirGrayHyst, 'canny', 1, 'nms', 20, 40)
threshold (ImaAmpGrayHyst, RegionGray, 1, 255)
skeleton (RegionGray, EdgesGray)
dev_display (GrayImage)
dev_set_color ('blue')
dev_display (EdgesGray)
Message := 'Segmented gray value edges'
disp_message (WindowHandle, Message, 'window', 12, 12, 'black', 'true')
stop ()
* Now display everything again, while only showing the part of the image
* containing the soccer field and the track.
Row1 := 220
Col1 := 215
Row2 := 399
Col2 := 489
dev_set_part (Row1, Col1, Row2, Col2)
dev_display (Image)
stop ()
dev_display (GrayImage)
stop ()
dev_display (ImaAmp)
stop ()
dev_display (ImaAmpGray)
stop ()
dev_display (Image)
dev_set_color ('blue')
dev_display (EdgesColor)
stop ()
dev_display (GrayImage)
dev_set_color ('blue')
dev_display (EdgesGray)

要点

1. 例程中着重说明图像中足球场和跑道两个区域间几乎没有对比度。以此为难点分别用edges_color和edges_image分割图像边缘。
   没有对比度意味着灰度化后足球场和跑道区域间边缘特征不明显(看起来像一块区域)，后接edges_image 确实没有检测出足球场边框。
   edges_color直接对彩色图像进行边缘提取，效果会好于edges_image方法。两个算子的参数相同，不同点在于入参图像分别为彩色图像和灰度图像。
   edges_color——使用 Deriche、Lanser、Shen 或 Canny 过滤器提取边缘；
    Image ——入参，待处理图像；
    ImaAmp ——出参，边缘幅度(梯度)分割结果；
    ImaDir ——出参，边缘方向分割结果；
    Filter ——入参，过滤器；
    Alpha ——入参，滤镜参数(值越小，平滑效果越强，细节越少，canny算子相反)；
    NMS ——入参，极大值抑制；
    Low ——入参，滞后阈值分割的低阈值(不需要则置negative)；
    High ——入参，滞后阈值分割的高阈值(不需要则置negative)；