The invention discloses an automatic detecting method, based on images, for arc scale labels of a pointer instrument. A single
digital camera is utilized to construct an image collecting
system and carry out calibration, two gauge outfit images are shot under drive signals corresponding to 20% of
full scale and 80% of
full scale, ruler line areas and scale line areas are achieved through
thresholding and
morphological processing, a framework is extracted, a candidate ruler disk center is decided on projection through a frame sectioning method, the ruler disk center and the
radius of the ruler lines are roughly detected and decided through a
hough transform circle, the least square fit is removed and
cut by two points to decide the accurate center and the
radius of the ruler lines, orientation angles of the scale lines on the ruler lines are decided through a
radial projection method to obtain a candidate scale base point, the obtained scale base point is decided and detected through co-domain, and results of two images are combined to obtain a final scale base
point set. The detecting method can automatically detect scale positions of arc ruler lines of the pointer instrument, can be applied to automatic calibration and automatic reading of the instrument, improves reading accuracy and reduces labor intensity.