... | ... | @@ -54,7 +54,9 @@ __In the case of low quality pictures__, each possible combination of active con |
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The optimization procedure uses the forces magnitude and orientation as parameters and try to minimize the difference between the computed photoelastic signal and the picture of disk. Different methods exist to compare two images, among them we have the Mean Squared Error (MSE) or the Structural Similarity Index (SSIM) [3,4]. The main advantage of the MSE is the speed of computation but it considers the image globally. On the opposite he SSIM is slower but considers region of the image to take into account its structure. Presently, for this application, both comparison criteria are similar, they are globally good but for some case failed to detect that the images do not match at all.
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> Here I would like to comute MSE and SSIM on the three particles given as example on the first figure.
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> <img src="uploads/46001dc532cf60a70fe7e5614e066855/SSIM_MSE.svg" width="400">
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> Comparison of SSIM and MSE index value on some particles (from Fig.1). The SSIM value range is between 0 and 1. The optimization process is a minimization process so we compute 1-SSIM.
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The optimization algorithm must be able to handle non-linear problem and possibly constraints to impose force and torque balance. If the chosen algorithm does not handle constraints, the equilibrium condition can either be impose by reducing the free parameters by 3 [1], or simply be skipped and assuming that the fitted pictures impose the torque and force balance.
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