Design Of Crop Height Measurement System Based On FPGA Ruler Image Recognition

The measurement of crop height is an important link in the automatic observation of crops,and it can directly reflect the growth of crops.This article combines image processing and FPGA hardware architecture to achieve automatic real-time crop height measurement.It can be widely used in automatic observation of crops or landscape plants.The measured plant height information is used to feed back plant growth status and guide the timing of manual intervention.This system acquires ruler images through a camera and enables crop plant height measurement by identifying an unblocked ruler.In this paper,we first investigate the specific algorithm for ruler image recognition and plant height measurement and verify it simulated;The design then implements an FPGA based image acquisition module and transplants image processing and plant height measurement algorithms onto the FPGA;Finally the FPGA based plant height measurement hardware system was tested and a crop height measurement experiment was performed.The main work completed in this paper includes:(1)Specific measurement of crop height was designed as follows: the ruler was placed and a ruler image was taken,the ruler image was segmented and filtered,the pixel heights of the scale color blocks were extracted,and the plant height was calculated by the proportional relationship of the single pixel and the actual height.The specific image processing algorithms were as follows: firstly,the ruler image was converted into HSV color space,and the segmentation threshold was determined by using software such as Sketchpad 3D to segment the ruler color blocks and binarize;Median filtering,closing operations,and removal of minimally connected domains were performed sequentially;Connected domain analysis was then performed to extract patch data;Crop height was finally calculated proportionally.In addition,simulation experiments are conducted to verify the feasibility of this crop height measurement scheme.(2)An image acquisition module is designed and implemented on the development board of FPGA,and the height measurement algorithm is transplanted to FPGA.Use SCCB bus to configure OV5640 camera module,drive LCD to realize image display;design and implement RGB565 to HSV module and threshold segmentation module.The shift register IP core is called to implement 3*3 and 7*7 filtering templates for median filtering and closing operation of binary image.Using adder and comparator instead of sorting process to realize median filtering of binary image.Using the counter to project the image horizontally,extract the connected area data and calculate the plant height,which improves the measurement accuracy to a certain extent.Finally,the simulation tests of each bottom module of FPGA are carried out.(3)In this paper,the crop height measurement experiments of Buxus microphylla and Ligustrum lucidum hedge are carried out.It takes 17.975 ms to process a 480*800 image by using FPGA,which is 2.84% of the processing time of MATLAB.This shows the real-time performance of FPGA system.The observation distance and the inclination of the ruler are tested respectively,and the relationship curve between the observation distance and the ruler range is fitted.In this system,the maximum observation distance is about 3.52 m,and the maximum range is 2.4m.The crop height can be measured 30 times per second.Finally,the complete crop height measurement system was tested with potted Jinsen Ligustrum Lucidum and Green Radish as experimental objects.The measurement are accurate to millimeters.The error was less than 1.35 cm and the maximum relative error was 3.55%,which met the first level standard of automatic observation of crop height.