Sometimes, images acquired for use in 2D or 3D digital image correlation tests can be too dark; noisy; blurry; or aliased. From time to time we are asked whether it would be beneficial to process these images in software such as Photoshop to fix these issues.
In short, this is never beneficial. The information content of the image was set in stone as soon as it was sent from the camera to the PC; further adjustments can change the look of the image, but will not improve your correlation results and may possibly hurt them. In the case of brightness, Vic-2D and Vic-3D will normalize the image internally; adding digital gain to the image will provide no benefit and may introduce quantization errors. Other processing (resizing, rotation, filtering) may cause problems because the interpolation algorithms in Vic-2D and Vic-3D are carefully designed to approximate known physical camera behaviors. Any soft postprocessing may create other artifacts. If an image is too dark to see well for the purposes of drawing an AOI or viewing result overlays, you can use the Histogram control in the toolbar to adjust the look of the image. This does not affect the correlation, but can make the image much easier to see and draw on.
Nick Lovaas
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