Halcon一日一练：图像拼接技术2:步骤与例程

上一篇主要介绍了图像拼接的一些原理和方法，这一篇将主要介绍步骤和例程：

接上一篇：

基于特征的接拼方法，分为四个步骤

1、特征检测：从图像中检测出显著且独特的图像特征，诸如：闭合区域，直线段，边缘，轮廓，点等。

2、特征匹配：从相似度确定图像之间特征的对应关系，又分为如下几类：

2.1：使用空域关系的方法

2.2：使用不变描述符的方法

2.3:松弛方法

2.4:金字塔和小波方法

3、变换模型的估计：变换函数选择和函数参数估计

4、图像变换和重采样：可以通过前向或后向的方式来实现，插值的方法有最近邻插值、双线性插值、双三次函数插值、二次样条插值、三次B样条插值、高阶B样条插值。

基于特征的方法普遍适用于局部结构信息更显著的情况，能够处理图像之间复杂变形的情况，不足之处是特征检测困难且不稳定，最关键的一点是需要有一种判断力很强的、鲁棒性能好的且对图像之间变化保持不变的特征匹配算法。

下面是Halcon自带例程，如何拼接图像

 **此例程讲解了如何将几张局部的PCB图像拼接居一张大的马赛克PCB图像。
 **此例程使用算子proj_match_points_ransac和算子 gen_projective_masaic完成上述工作。
 **请注意：这个PCB图像有一几处看起来像拼接逢合线的破损点，为了更好的区分真正的缝合线，例程呈现逢合线。
 dev_update_off ()
 dev_close_window ()
 dev_open_window (, , , , 'white', WindowHandle)
 dev_set_color ('green')
 set_display_font (WindowHandle, , 'mono', 'true', 'false')
 **一张一张的读取图像。
 gen_empty_obj (Images)
 for J :=  to  by
     read_image (Image, 'mosaic/pcb_' + J$'')
     concat_obj (Images, Image, Images)
     dev_display (Image)
     disp_message (WindowHandle, 'Image ' + J$'d', 'image', -, -, 'black', 'true')
     wait_seconds ()
 endfor
 disp_continue_message (WindowHandle, 'black', 'true')
 stop ()
 * To show the point matches that are used to compute the projective
 * transformation between the images, we will show all images in a large
 * tiled image with some space between the images so that the extents
 * of the images are easily visible.
 dev_set_window_extents (-, -,  / ,  / )
 tile_images_offset (Images, TiledImage, [,,,,,], [,,,,,], [-,-,-,-,-,-], [-,-,-,-,-,-], [-,-,-,-,-,-], [-,-,-,-,-,-], , )
 dev_clear_window ()
 dev_display (TiledImage)
 disp_message (WindowHandle, 'All 6 images', 'window', , , 'black', 'true')
 disp_message (WindowHandle, 'Click \'Run\'\nto continue', 'window',  /  - , , 'black', 'true')
 stop ()
 * Now we compute point matches between the five pairs of images and with this
 * the projective transformation between the image pairs.  Note that the code
 * below calls the point operator for each image pair.  Since the images form
 * a strip, with a little book keeping we could make the process a little more
 * efficient by saving the points from the last iteration (ImageT in pair J will
 * be identical to ImageF in pair J+).  This is not done here because such an
 * optimization would be quite cumbersome in the general case where the images
 * can lie in a general configuration that cannot be represented by a strip.
 dev_clear_window ()
 dev_display (TiledImage)
 disp_message (WindowHandle, 'Point matches', 'window', , , 'black', 'true')
 * We define the image pairs, i.e., which image should be mapped to which image.
 From := [,,,,]
 To := [,,,,]
 Num := |From|
 * We need a variable to accumulate the projective transformation matrices.
 ProjMatrices := []
 * Furthermore, since we want to create a rigid mosaic below we need to
 * accumulate all the point correspondences and the number of matches per
 * image pair.
 Rows1 := []
 Cols1 := []
 Rows2 := []
 Cols2 := []
 NumMatches := []
 * Now we can determine the transformations between the five image pairs.
 for J :=  to Num -  by
     F := From[J]
     T := To[J]
     select_obj (Images, ImageF, F)
     select_obj (Images, ImageT, T)
     * Extract the points in both images.
     points_foerstner (ImageF, , , , , 0.3, 'gauss', 'false', RowJunctionsF, ColJunctionsF, CoRRJunctionsF, CoRCJunctionsF, CoCCJunctionsF, RowAreaF, ColAreaF, CoRRAreaF, CoRCAreaF, CoCCAreaF)
     points_foerstner (ImageT, , , , , 0.3, 'gauss', 'false', RowJunctionsT, ColJunctionsT, CoRRJunctionsT, CoRCJunctionsT, CoCCJunctionsT, RowAreaT, ColAreaT, CoRRAreaT, CoRCAreaT, CoCCAreaT)
     * Determine the point matches and the transformation for the current
     * image pair.
     proj_match_points_ransac (ImageF, ImageT, RowJunctionsF, ColJunctionsF, RowJunctionsT, ColJunctionsT, 'ncc', , , , , , , 0.5, 'gold_standard', , , ProjMatrix, Points1, Points2)
     * Accumulate the transformation matrix.
     ProjMatrices := [ProjMatrices,ProjMatrix]
     * Accumulate the point matches and number of point matches.
     Rows1 := [Rows1,subset(RowJunctionsF,Points1)]
     Cols1 := [Cols1,subset(ColJunctionsF,Points1)]
     Rows2 := [Rows2,subset(RowJunctionsT,Points2)]
     Cols2 := [Cols2,subset(ColJunctionsT,Points2)]
     NumMatches := [NumMatches,|Points1|]
     * Generate crosses that represent the extracted points in the tiled image.
     * Note that we have to take the row offsets of the images in the tiled image
     * into account.
     gen_cross_contour_xld (PointsF, RowJunctionsF + (F - ) * , ColJunctionsF, , rad())
     gen_cross_contour_xld (PointsT, RowJunctionsT + (T - ) * , ColJunctionsT, , rad())
     * Generate a representation of the matched point pairs as lines.  We create
     * XLD contours from the lines so that we can zoom into the graphics window
     * to take a closer look at the matches.
     RowF := subset(RowJunctionsF,Points1) + (F - ) *
     ColF := subset(ColJunctionsF,Points1)
     RowT := subset(RowJunctionsT,Points2) + (T - ) *
     ColT := subset(ColJunctionsT,Points2)
     gen_empty_obj (Matches)
     for K :=  to |RowF| -  by
         gen_contour_polygon_xld (Match, [RowF[K],RowT[K]], [ColF[K],ColT[K]])
         concat_obj (Matches, Match, Matches)
     endfor
     * Now display the extracted data.
     dev_set_color ('blue')
     dev_display (Matches)
     dev_set_color ('green')
     dev_display (PointsF)
     dev_display (PointsT)
 endfor
 disp_message (WindowHandle, 'Click \'Run\'\nto continue', 'window',  /  - , , 'black', 'true')
 stop ()
 * Finally, we can generate the mosaic image from the projective transformations.
 gen_projective_mosaic (Images, MosaicImage, , From, To, ProjMatrices, 'default', 'false', MosaicMatrices2D)
 get_image_size (MosaicImage, Width, Height)
 dev_set_window_extents (-, -, Width / , Height / )
 dev_clear_window ()
 dev_display (MosaicImage)
 disp_message (WindowHandle, 'Projective mosaic', 'window', , , 'black', 'true')
 disp_message (WindowHandle, 'Click \'Run\'\nto continue', 'window', Height /  - , , 'black', 'true')
 stop ()
 * To show more clearly that the folds visible in the image do not result from the
 * mosaicking, we display the seams between the images in the mosaic image.
 * This can be done most easily by creating an image that contains the border
 * of the images, generating a mosaic from it, and segmenting the resulting
 * mosaic image.
 get_image_size (Image, Width, Height)
 gen_image_const (ImageBlank, 'byte', Width, Height)
 gen_rectangle1 (Rectangle, , , Height - , Width - )
 paint_region (Rectangle, ImageBlank, ImageBorder, , 'margin')
 gen_empty_obj (ImagesBorder)
 for J :=  to  by
     concat_obj (ImagesBorder, ImageBorder, ImagesBorder)
 endfor
 gen_projective_mosaic (ImagesBorder, MosaicImageBorder, , From, To, ProjMatrices, 'default', 'false', MosaicMatrices2D)
 threshold (MosaicImageBorder, Seams, , )
 dev_clear_window ()
 dev_display (MosaicImage)
 disp_message (WindowHandle, 'Seams between the\nimages', 'window', , , 'black', 'true')
 dev_set_color ('yellow')
 dev_display (Seams)
 disp_message (WindowHandle, 'Click \'Run\'\nto continue', 'window', , , 'black', 'true')
 stop ()
 * If you look very closely at the projective mosaic above, you may note that
 * there is a very slight projective distortion in the mosaic.  This happens
 * because the transformations cannot be determined with perfect accuracy
 * because of very small errors in the point coordinates due to noise.  Because
 * of the strip configuration, essentially the overlapping area between the image
 * pairs can act like a hinge around which the images may rotate out of the image
 * plane.  In this example, we know that the mapping between the images must
 * be a rigid transformation.  If we want to force the transformation to be rigid
 * we can simply use bundle_adjust_mosaic.
 bundle_adjust_mosaic (, , From, To, ProjMatrices, Rows1, Cols1, Rows2, Cols2, NumMatches, 'rigid', MosaicMatrices2D, Rows, Cols, Error)
 * Now, we can generate the mosaic image from the rigid transformations.
 gen_bundle_adjusted_mosaic (Images, MosaicImageRigid, MosaicMatrices2D, 'default', 'false', TransMatrix2D)
 get_image_size (MosaicImageRigid, Width, Height)
 dev_set_window_extents (-, -, Width / , Height / )
 dev_clear_window ()
 dev_display (MosaicImageRigid)
 disp_message (WindowHandle, 'Rigid mosaic', 'window', , , 'black', 'true')

带逢合线的图像                    找定位点

最终图像：

下面我们看一下另一个例程：

这个例程使用proj_match_points_ransac_guided 和 gen_projective_mosaic

主要介绍如何使用金字塔算法快速获取两个图像的特征点进行拼接。

 * This example program shows how images can be combined
 * into a mosaic image using proj_match_points_ransac_guided
 * and gen_projective_mosaic.
 * It is shown how the calculation of the projection between two
 * images can be accelerated using an image pyramid.
 *
 * Initializations
 ImgPath := '3d_machine_vision/mosaic/'
 ImgName := 'bga_r_'
 Times := []
 Colors := ['red','coral','yellow','lime green']
 read_image (Images, ImgPath + ImgName + ['',''])
 dev_update_off ()
 dev_close_window ()
 dev_open_window_fit_size (, , , , , , WindowHandle)
 dev_open_window_fit_size (, , , , , , WindowHandle1)
 set_display_font (WindowHandle, , 'mono', 'true', 'false')
 set_display_font (WindowHandle1, , 'mono', 'true', 'false')
 * The internal camera parameters of the used camera
 * (necessary to eliminate radial distortions)
 CamParam := [0.0121693,-2675.63,7.40046e-006,7.4e-006,290.491,258.887,,]
 change_radial_distortion_cam_par ('adaptive', CamParam, , CamParOut)
 change_radial_distortion_image (Images, Images, Images, CamParam, CamParOut)
 * To show the point matches that are used to compute the
 * transformation between the images, we will show both images in a
 * tiled image with some space between the images so that the extents
 * of the images are easily visible.
 tile_images_offset (Images, TiledImage, [,], [,], [-,-], [-,-], [-,-], [-,-], , )
 *
 * Now we can determine the transformations between the image pairs.
 From :=
 To :=
 select_obj (Images, ImageF, From)
 select_obj (Images, ImageT, To)
 *
 * Repeat the calculation  times with a different number of pyramid levels
 for NumLevels :=  to  by
     *
     dev_clear_window ()
     dev_set_window (WindowHandle)
     dev_clear_window ()
     dev_display (TiledImage)
     disp_message (WindowHandle, ['Calculate point matches','with ' + NumLevels + ' pyramid levels','Please wait ...'], 'window', , , 'black', 'true')
     *
     * Calculate the projection between the two images
     * Check the procedure's comments for details
     count_seconds (S1)
     proj_match_points_ransac_pyramid (ImageF, ImageT, NumLevels, RowFAll, ColFAll, RowTAll, ColTAll, ProjMatrix, Points1, Points2)
     count_seconds (S2)
     Times := [Times,S2 - S1]
     *
     * Display point correspondences
     gen_cross_contour_xld (PointsF, RowFAll, ColFAll, , rad())
     gen_cross_contour_xld (PointsT, RowTAll + , ColTAll, , rad())
     RowF := subset(RowFAll,Points1)
     ColF := subset(ColFAll,Points1)
     RowT := subset(RowTAll,Points2) +
     ColT := subset(ColTAll,Points2)
     gen_empty_obj (Matches)
     for K :=  to |RowF| -  by
         gen_contour_polygon_xld (Match, [RowF[K],RowT[K]], [ColF[K],ColT[K]])
         concat_obj (Matches, Match, Matches)
     endfor
     dev_display (TiledImage)
     dev_set_color ('blue')
     dev_display (Matches)
     dev_set_color ('green')
     dev_display (PointsF)
     dev_display (PointsT)
     disp_message (WindowHandle, [|RowF| + ' point matches','Time used: ' + (S2 - S1)$'.3' + ' s'], 'window', , , 'black', 'true')
     *
     * Generate the mosaic image
     gen_projective_mosaic (Images, MosaicImage, , From, To, ProjMatrix, [,], 'false', MosaicMatrices2D)
     *
     * Display mosaic image
     get_image_size (MosaicImage, Width, Height)
     dev_set_window (WindowHandle1)
     dev_resize_window_fit_image (MosaicImage, , , [,], )
     dev_clear_window ()
     dev_display (MosaicImage)
     disp_message (WindowHandle1, 'Projective mosaic (used ' + NumLevels + ' pyramid levels)', 'window', , , 'black', 'true')
     disp_continue_message (WindowHandle1, 'black', 'true')
     stop ()
 endfor
 *
 * Display execution times
 dev_set_window (WindowHandle)
 dev_close_window ()
 MaxTime := max(Times)
 BaseRow :=
 RectHeight :=
 disp_message (WindowHandle1, ['Time in s:','(#levels used)'], 'image', BaseRow + , , 'black', 'true')
 for Index :=  to |Times| -  by
     gen_rectangle1 (Rectangle, BaseRow - RectHeight * Times[Index] / MaxTime,  + Index * , BaseRow,  + Index * )
     disp_message (WindowHandle1, [Times[Index]$'.3','(' + (Index + ) + ')'], 'image', BaseRow + ,  +  * Index, 'black', 'true')
     dev_set_color (Colors[Index])
     dev_set_draw ('fill')
     dev_display (Rectangle)
 endfor
 disp_finished_message (WindowHandle1, 'black', 'true')