Abstract: A variable-rate spray system of fruiter needs real-time detection for the fruiter
crown diameter. Existing digital image processing technology can not realize real-time detection
for the fruiter crown diameter. The problem is that the detection error is large or no error can be
detected. A reference standard plate with fruiters when capturing images is used to obtain the
fruiter crown diameter by calculating image unit pixel width in this paper. Comparing with the
reference crown diameter detected by the handheld laser rangefinder, test results show that 74% of
the test sample of 50 fruiters have a relative difference of less than 20% between the crown
diameters detected by the image processing method and the reference values. The regression
analysis of fruiter crown diameter on digital image detection value and the reference one shows
R2=0.7406.

Key words: Variable-rate spray, fruiter crown diameter, digital image, real-time detection