During hot fire rocket engine testing, non-contacting measurements are superior to bonded gauges because they are immune to burning, shaking loose, or damage due to the harsh testing conditions. Additionally, when compared to instruments which register at single points, Digital Image Correlation (DIC) has the added benefit in that it collects full-field displacement and strain maps over the duration of the test. However, for certain materials and paints under some circumstances of temperature and camera sensitivity, portions of the speckle pattern which were darker at room temperature may emit more light compared to the initially lighter portions of the pattern, resulting in a high temperature pattern which is inverted in comparison with that at room temperature. To address this inversion, a post-processing method is introduced wherein an inverted image containing only emitted light is subtracted from an image containing both emitted and reflected light, thereby generating an un-inverted image. The artificial high temperature image is subsequently correlated against the room temperature image to obtain full-field strains. The subtraction technique is then validated using optical bandpass filters to prevent significant amounts of emitted light from reaching the camera sensor. The two methods are mapped onto common coordinates and shown to produce comparable results. The subtraction method sufficiently mitigates speckle pattern inversion, but its key drawback is that it only works when there is negligible displacement between the subtracted images (i.e. quasi-static loading). It is therefore preferable to eliminate inversion from reaching the camera in the first place by using optical bandpass filters.

在热火火箭发动机测试期间，非接触式测量优于粘结式量规，因为它们不受恶劣的测试条件影响而燃烧，晃动或损坏。此外，与在单点记录的仪器相比，数字图像相关性（DIC）具有更多的优势，因为它可以在测试过程中收集全场位移和应变图。但是，对于某些材料和涂料，在某些温度和照相机感光度的情况下，与最初较亮的图案部分相比，在室温下较暗的斑点图案部分可能会发射更多的光，从而导致高温图案被倒置与室温下相比。为了解决这种反转，引入了一种后处理方法，其中从包含发射光和反射光的图像中减去仅包含发射光的反相图像，从而生成非反相图像。随后将人造高温图像与室温图像相关联，以获得全场应变。然后使用光学带通滤光片验证减法技术，以防止大量的发射光到达相机传感器。两种方法都映射到公共坐标上，并显示出可比较的结果。减法充分地减轻了斑点图案的反转，但是其主要缺点是，仅当相减后的图像之间的位移可忽略不计（即准静态载荷）时，该方法才有效。