Research On Calibration Of Online Imaging Luminance Meter Based On CMOS

Color coordinates and luminance are two important parameters for evaluating the quality of light-emitting LED products.Traditional color coordinate and luminance measurement methods use a chromatograph and a luminance meter,which are time-consuming,labor-intensive,costly,and inconvenient to carry.With the development of digital image processing technology and CMOS image sensor technology,an imaging photometer made of color CMOS industrial cameras can measure both color coordinates and luminance.This method is time-saving,efficient,simple to operate,and low-cost.,It is gradually getting people's favor in the measurement of industrial optical parameters.However,due to the dark current of the color CMOS industrial camera itself and the limitation of its imaging by the color temperature of the light source and other factors,the online imaging luminance meter based on CMOS will produce measurement errors in actual use.To reduce this error,the online imaging luminance meter based on CMOS has been widely used.In this paper,the reference method is used to study the color coordinate and luminance calibration of this imaging type luminance meter.Aiming at the problem of the error in the color coordinate measurement of the imaging type luminance meter,this paper improves the gray world algorithm to realize the color coordinate calibration of the imaging type luminance meter.First,the improvement of the gray world algorithm is completed by weighted calculation of the gain coefficient of each color component,and the improved algorithm is quantitatively analyzed with the white balance evaluation index to verify the feasibility of the algorithm.Secondly,the improved gray world algorithm is used to perform white balance processing on the image collected by the imaging luminance meter to complete the calibration of the color coordinate.Finally,the calibrated imaging type luminance meter is applied to the color coordinate detection of the luminous characters on the surface of the car handle.The experimental results show that the color coordinate indication error of the calibrated imaging luminance meter can meet the expected index requirements,which proves the reliability of the color coordinate calibration method in this paper.Aiming at the problem of the error in the luminance measurement of the imaging type luminance meter,this paper proposes a method that combines the dark current calibration and the nonlinear calibration to calibrate the imaging type luminance meter.In the dark current calibration part,this article adopts the method of controlling program-controlled parameters to suppress the influence of dark current on the luminance measurement value.Based on dark current calibration,a segmented method is proposed to establish the nonlinear model of the imaging luminance meter under different luminance measurement ranges of high and low respectively,to reduce the measurement error of the imaging luminance meter due to the small dynamic range.Finally,the calibrated imaging type luminance meter is applied to the luminance detection of the luminous characters on the surface of the car handle.The experimental results show that the average brightness error of the calibrated imaging luminance meter meets the expected index requirements,which proves that the luminance calibration method proposed in this paper has certain feasibility.