ID 186

Analysis of backlight images for spray measurement: how to accurately identify the liquid-gas interface in images

 

Abstract:

We present in this paper the key points for using backlight images in spray measurement. The main features of a spray accessible from backlight images are the interface contours of the liquid elements. It is commonly considered that using this kind of images is straightforward, notably because these images are directly understandable by a human being. However, making image-based measurement needs a rigorous approach. The first point is the setting up of the optical system. Although no special expertise is required to make images of sprays, a particular attention must be put on the imaging system and light source arrangements when relevant measurement are expected. Also, different steps must be considered to correctly estimate liquid-gas interface localization on backlight images. Fist, attention must be put on the pretreatment of the images to correct light source defects such as spatial or temporal in-homogeneity. For the segmentation step that follows, local intensity variations in the images are analyzed to determine the localization of the liquid-gas interface contour in the images. It is shown that modeling the image of liquid elements is mandatory to correctly estimate this features. Based on the results of this modeling, several local parameters are proposed. It is shown how the local shape of the interface acts on the variation of these parameters. Finally, partial overlapping of images of liquid elements is considered and solutions for discriminating potential overlapping liquid elements in an image are proposed.