Preventing Heat-Induced Image Warping in Machine Vision Line Scan Cameras I t is well known from astronomical imaging that various atmospheric conditions and weather effects have an impact on image quality. This is due to local changes of the refractive index of the air in the optical path. These changes are wavelength-dependent and vary with changes in the atmospheric pressure and its humidity. In the field of machine vision, both pressure and humidity can usually be assumed to be constant over the whole optical path. However, there is an exception to this rule if there are turbulent air currents in the optical path that may cause local pressure changes. A typical cause for turbulences is heat convection between parts at different temperatures. Common heat sources in machine vision can be either the illumination, high-load electronics, or high temperature samples such as poured metal. turbulent air act as a gradient lens that warps the image content in the affected areas. The magnitude and extension of the warping is both too complex and too dependent on the setup to model mathematically. Instead, we show an example measurement of this effect to represent its typical magnitude and to guide you in measuring it in your own setup. In a line scan camera, the optical distortion is constant for each line along the scanning direction and is therefore not visible in the image. This fact reduces the problem to one spatial dimension - perpendicular to the scan direction - and the time dimension. Both dimensions can be observed at once by acquiring an image of a static target with the line scan camera. The optical distortion will shift the position of the image content in x-direction while the extension of the warping in y-direction represents the time information. This shift can easily be measured by imaging a static line pattern. The basic principle of this measurement is depicted in Figure 1. A reference image intensity profile is taken by averaging a region of interest containing an area of a few columns around each x-position (depicted in green). A square test block (depicted in red) is passed along the whole column and for each position the test data is shifted in subpixel steps via Influence on Imaging asharkyu/Shutterstock.com The different refractive indices in the 8 Photonics & Imaging Technology, May 2021 Cov ToChttp://www.abpi.net/ntbpdfclicks/l.php?202105TBNAV