基于尺度时间均衡的高速风洞视频测量图像闪烁修正方法

Flicker compensation method based on scale-time equalization for videogrammetric measurement images in high speed wind tunnels

高速风洞视频测量试验环境中,复杂的光照条件容易导致采集的图像序列出现闪烁,影响测量结果的精度。在测量图像中,由于照明变化导致的灰度变化和目标运动、变形引起的局部变化耦合在一起,导致基于仿射变换模型(线性或非线性)的修正方法难以适用。尺度时间的直方图均衡方法(STE)利用尺度空间理论,对各图像直方图中每一个灰度值组成的曲线在时间维度上进行高斯卷积得到目标直方图,再通过直方图匹配获得闪烁修正后的图像。针对日光灯照明下的相机标定板图像、存在运动和变形的风洞模型变形测量试验图像和存在油膜形态变化的油流试验图像开展了应用研究。结果表明,该方法适用于图像序列的全局闪烁修正,与基于模型的方法相比,其修正效果不依赖于基准图像,对图像抖动、局部存在目标运动或变形等干扰因素的鲁棒性强,且方法简单,计算量小,具有较高的工程应用价值。

The complex illumination conditions in the high-speed wind tunnels can easily lead to the flicker of the videogrammetric measurement(VM)test image sequences,which affect the accuracy of the measurement result.As the flicker contains both the global change of the gray level caused by the illumination and the local change caused by the object motion,deformation and so on,it is difficult to apply the compensation methods based on affine transformation model(linear or non-linear)between pixels or between blocks of the images.Based on the scale space theory,the scale-time equalization(STE)method was proposed by Delon(2006)and applied to correct flicker in video and movie.The STE method performs the Gaussian convolution in the time dimension of each gray value in the histograms to obtain the target histogram of each image,and then uses histogram matching to get the flicker compensated images.Three experiments with different flicker and interference were conducted:the camera calibration plate image under the fluorescent lighting,the deformation test image of the wind tunnel model and the cavity oil film test image with diffusion.The experimental results show that the STE method is suitable for the global flicker compensation of the VM test image sequence.Compared with the model-based methods,the flicker compensation effect is not dependent on the reference image,and the robustness to the interference factors such as image jitter,local motion or deformation is strong.Meanwhile,the method has the advantages of simple procedures and small computation cost,and therefore it has high engineering application value.