halcon知识：dyn_threshold的用法（划痕检测）

一、dyn_threshold算子说明

dyn_threshold(OrigImage, ThresholdImage : RegionDynThresh : Offset, LightDark : )

• dyn_threshold 从输入的两幅图像中选择像素满足阈值条件的区域。
• 令 g_{o} = g_{OrigImage} 和 g_{t} = g_{ThresholdImage}。
• 其中，g_{OrigImage}是原始图像，g_{ThresholdImage}是平滑后图像，充当阈值。

那么

1） LightDark = 'light' 的条件是：

                                                        

2）对于 LightDark = 'dark'，条件是：

                                                         

3）对于 LightDark = 'equal'，条件是：

                            

4)对于 LightDark = 'not_equal'，条件是：

                            

通常，阈值图像是原始图像的平滑版本（例如，通过应用 mean_image、binomial_filter、gauss_filter 等）。那么 dyn_threshold 的效果类似于将阈值应用于原始图像的高通滤波版本（参见 highpass_image）。

二、针对问题:

2.1 原始图片

如下图中，将划痕部分检出来。

read_image (Image, 'surface_scratch')

• 原始图的表面灰度图（看不出明显的划痕）。

2.2 平滑后的图片

mean_image (Image, ImageMean, 7, 7)

平滑图片灰度图（划痕明显）：

 2.3 观察结果

可以断定，平滑图片中，能够将被噪声湮灭的细长划痕的信号给暴露出来。

三、代码部分

* This programm shows the extraction of surface scratches via
* local thresholding and morphological post-processing
* 
dev_update_off ()
dev_close_window ()
* 
* Step 1: Acquire image
* 
read_image (Image, 'surface_scratch')
get_image_size (Image, Width, Height)
dev_open_window_fit_image (Image, 0, 0, Width, Width, WindowID)
set_display_font (WindowID, 16, 'mono', 'true', 'false')
dev_set_draw ('margin')
dev_set_line_width (4)
dev_display (Image)
Message := 'This program shows the extraction of'
Message[1] := 'surface scratches via local thresholding'
Message[2] := 'and morphological post-processing'
disp_message (WindowID, Message, 'window', 12, 12, 'black', 'true')
disp_continue_message (WindowID, 'black', 'true')
stop ()
* 
* Step 2: Segment image
* 
* Using a local threshold
mean_image (Image, ImageMean, 7, 7)
dyn_threshold (Image, ImageMean, DarkPixels, 5, 'dark')
* 
* Extract connected components
connection (DarkPixels, ConnectedRegions)
dev_set_colored (12)
dev_display (Image)
dev_display (ConnectedRegions)
Message := 'Connected components after image segmentation'
Message[1] := 'using a local threshold.'
disp_message (WindowID, Message, 'window', 12, 12, 'black', 'true')
disp_continue_message (WindowID, 'black', 'true')
stop ()
* 
* Step 3: Process regions
* 
* Select large regions
select_shape (ConnectedRegions, SelectedRegions, 'area', 'and', 10, 1000)
dev_display (Image)
dev_display (SelectedRegions)
disp_message (WindowID, 'Large Regions', 'window', 12, 12, 'black', 'true')
disp_continue_message (WindowID, 'black', 'true')
stop ()
* 
* Visualize fractioned scratch
open_zoom_window (0, round(Width / 2), 2, 303, 137, 496, 3, WindowHandleZoom)
dev_set_color ('blue')
dev_display (Image)
dev_display (SelectedRegions)
set_display_font (WindowHandleZoom, 16, 'mono', 'true', 'false')
disp_message (WindowHandleZoom, 'Fractioned scratches', 'window', 12, 12, 'black', 'true')
disp_continue_message (WindowHandleZoom, 'black', 'true')
stop ()
* 
* Merge fractioned scratches via morphology
union1 (SelectedRegions, RegionUnion)
dilation_circle (RegionUnion, RegionDilation, 3.5)
dev_display (Image)
dev_display (RegionDilation)
Message := 'Region of the scratches after dilation'
disp_message (WindowHandleZoom, Message, 'window', 12, 12, 'black', 'true')
disp_continue_message (WindowHandleZoom, 'black', 'true')
stop ()
skeleton (RegionDilation, Skeleton)
connection (Skeleton, Errors)
dev_set_colored (12)
dev_display (Image)
dev_display (Errors)
Message := 'Fractioned scratches merged via morphology'
disp_message (WindowHandleZoom, Message, 'window', 12, 12, 'black', 'true')
disp_continue_message (WindowHandleZoom, 'black', 'true')
stop ()
* 
* Distinguish small and large scratches
close_zoom_window (WindowHandleZoom, Width, Height)
select_shape (Errors, Scratches, 'area', 'and', 50, 10000)
select_shape (Errors, Dots, 'area', 'and', 1, 50)
dev_display (Image)
dev_set_color ('red')
dev_display (Scratches)
dev_set_color ('blue')
dev_display (Dots)
Message := 'Extracted surface scratches'
Message[1] := 'Not categorized as scratches'
disp_message (WindowID, Message, 'window', 440, 310, ['red','blue'], 'true')

检查结果： 

总结：

• 灰度低通滤波可以突出信号。
• dyn_threshold可以对两幅孪生图的信号进行阈值分割。