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Accurate measurement of the line spacing of the reticle is the key to ensure the accuracy of lens focal length measurement. However, due to the manufacturing process, there are spacing errors, line width errors and length errors in the line. One of the spacing errors is compensated by calibration, while the other two manufacturing errors also have an impact on the positioning accuracy of the scribe positioning algorithm. Therefore, by analyzing the principle of the line pattern positioning algorithm, the error model of the line positioning error caused by manufacturing error is established. In order to reduce the impact of the line manufacturing error on the line location results, this paper proposes a line global pixel fitting algorithm. On the basis of the edge fitting method, all the pixel contained in the scribing are used to fit, and the pixels with large deviation are found and eliminated by Grubbs. After all the pixels with large deviation are removed, the pixel set is fitted by least squares to get the line position. Through experimental comparison, the global pixel fitting algorithm is not affected by the manufacturing error of the marking line, and has strong resistance to noise. The measurement error is less than 0.08 pixels, and the standard deviation is 0.023 pixels.
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