The maximum of the correlation window will be interpolated (using Taylor expansion over a 3x3 neighborhood), giving a better estimate of its position. Interpolate: if checked, the analysis will perform for each pixel an additional step, allowing to get sub-pixel flow magnitude.That is the size of the blocks that will be compared to get a flow out of it. Window size: sets the interrogation window size for analysis.Reference that can be seen in the color wheel.Įrror creating thumbnail: Unable to save thumbnail to destination The color encode flow direction and magnitude, using the This effectively generate a sort ofīelow is what the PIV analysis found, with a window of 64圆4 (the max displacement theĪlgorithm can find is given by half of the window size, so we had to go for at least 50x50), With α=25 and Xm and Ym half of the image width. Second frame was obtained by adding a shift to each blob, given by: The image to the right is made of 2000 small gaussian blobs (sigma=1), spawned randomly The plugin is now multi-threaded, meaning that it will analyze multipleįrame couples at once, depending how many CPUs it can find. I recommend downsampling the images, this wouldĭiminish the density of results, but make this plugin affordable. Size of 8x8, the plugin, the plugin can process a stack of 200x200 inĪpproximately 1 second. Typically, on a MacBook (grey model, 2009), for an 8-bit stack with a window Left), but the whole correlation matrix is recalculated from scratch (a lot Only a little (only one column is replaced actually, and the rest is shifted This is a highly redundant process, for when theĪlgorithm moves to the next pixel to the right, the blocks content change Is then calculated from these two blocks, and the result is analyzed to Is extracted for the front image and the back image. For each pixel away from the border of the image, a block The trade off is loss of precision, but also theįact that you might get completely irrelevant vectors.Īs stated before, this plugin implements a very naive and primitiveĪlgorithm, without a sense of subtlety, and exists mainly forĮducational purpose. Track them, which makes it particularly interesting when dealing withīrightfield or DIC images. Of a velocity field without having to segment objects out of an image and įor us, the main interest of this technique is that it allows the computation
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