Image Pre-Processing

For each test, TOPINS requires two images: one image with a clear view of the grid board (Background Grid Picture), and one or more images with a view of the same board as seen through a transparency (Foreground Glass Picture). Because of this, all Foreground Glass Pictures used in a single test share the same Background Grid Picture.

Preprocessing of a Background Grid Picture needs to be done only once per test, but the procedure needs to be repeated separately for each transparency. In order to avoid any image imperfection, TOPINS has dedicated tools to correct it – Sensitivity Threshold and Minimum Length.

During the PREPROCESSING stage, TOPINS analyzes the image of the reference grid and an image of the reference grid as seen through the examined transparency, extracts the locations of the lines on the grid, and creates internal vectorization interpretations of them. With a clear view of the grid, those vectors will be almost straight lines. When the grid is viewed through a transparency, those vectors will usually be distorted in some zones.

The most common causes of the transparency distortion are non-uniform thickness of transparency, excessive curvature of transparency, heat induced stress, structural stress generated during the installation of transparency into the canopy frame and the installation of a canopy on the aircraft. Due to distorted transparency, objects viewed through it can be magnified, lengthened, misshapen, or their movement can be misjudged, etc.

Nowadays, the method which is most often used to measure the degree of optical distortion in the transparency utilizes a double exposure photographic procedure. Usually, that method is based on the international standards (e.g. ASTM) and obtained data are mainly processed manually. However, this method has proved to be slow, inefficient and highly susceptible to subjective interpretation by all links in the quality assurance chain, from the  transparency manufacturer to the pilot as the end user.

TOPINS is a stand-alone MS Windows application enabling high-precision automated and efficient distortion measurement across the entire visual field of the transparency. Distortion is measured according to one and/or multiple selected standards. TOPINS has been developed to meet the highest standards of quality assurance in transparency inspection and eliminate any subjective factors from the process. The PDM system is an important feature of TOPINS software that manages all relevant data and technical documentation relating to the examined transparency.