How the results of this picture are expressed in Image j
@pujyunshyang Are you asking how ImageJ deals with orientation lines? Or how to generate orientation lines algorithmically?
How ImageJ supports drawing such lines: ImageJ has support for regions of interest (ROIs), which are measurements (especially areas and lines) on top of your image. You can use the ROI Manager to collect more than one ROI at once. You can also use overlays to draw a set of ROIs as a non-destructive layer on top of your image. Either the ROI Manager or overlays will enable you to visualize a collection of orientation lines like that.
How ImageJ can compute them from an image: You need an algorithm. One plugin is Directionality; perhaps others here will recommend alternatives. E.g., my group (LOCI/Eliceiri lab) studies collagen fiber alignment and developed a non-ImageJ tool called CurveAlign for extracting fiber alignments.
Thank you for your answer, this answer helped me