5 ms·

I don't fully understand the process of creating 3D video from 2D slices. Is that some sort of holographic procedure? Presumably such a video could also easily

by singularity2001 8y ago

I don't fully understand the process of creating 3D video from 2D slices. Is that some sort of holographic procedure? Presumably such a video could also easily be computed from CAD models, right?

yorwba 8y ago
Reconstructing 3D models from 2D projections is a popular exercise in applied linear algebra courses (actually, 2D images from 1D projections are more common, because it's easier to visualize). The procedure is pretty easy to code up once you've understood the mathematics. Essentially you build a system of linear equations describing the influence of material density on the measured intensity, then solve it for density given intensity. https://scikit-learn.org/stable/auto_examples/applications/plot_tomography_l1_reconstruction.html https://scikit-learn.org/stable/auto_examples/applications/p... Generating projections from a model is much easier, because you only need to write the rendering pass and don't have to invert it.
Someone 8y ago
Producing 3D images from 2D slices is easy. The problem is that the 2D images that a CT machine makes aren’t slices, but projections of the 3D volume onto various planes. For example, if your image is ......... ..x...x.. ......... ....x.... .x.....x. ..xxxxx.. ......... an image taken vertically will count the x-es in each column: 012121210 and one taken from the left or right will count them in each row: 0 2 0 1 2 5 0 Those 2 projections (probably; I haven’t checked this image) aren’t sufficient to reconstruct the image, but they already add significant constraints. For example, those 5 X-es in the next to last row can’t be in the first or last column (if they were there, the first image would start or end with a non-zero value) The more projections you add at other than orthogonal angles, the more constrained the solutions become.

I don't fully understand the process of creating 3D video from 2D slices. Is that some sort of holographic procedure? Presumably such a video could also easily be computed from CAD models, right?

yorwba 8y ago

Reconstructing 3D models from 2D projections is a popular exercise in applied linear algebra courses (actually, 2D images from 1D projections are more common, because it's easier to visualize). The procedure is pretty easy to code up once you've understood the mathematics. Essentially you build a system of linear equations describing the influence of material density on the measured intensity, then solve it for density given intensity. https://scikit-learn.org/stable/auto_examples/applications/plot_tomography_l1_reconstruction.html https://scikit-learn.org/stable/auto_examples/applications/p... Generating projections from a model is much easier, because you only need to write the rendering pass and don't have to invert it.

Someone 8y ago

Producing 3D images from 2D slices is easy. The problem is that the 2D images that a CT machine makes aren’t slices, but projections of the 3D volume onto various planes. For example, if your image is ......... ..x...x.. ......... ....x.... .x.....x. ..xxxxx.. ......... an image taken vertically will count the x-es in each column: 012121210 and one taken from the left or right will count them in each row: 0 2 0 1 2 5 0 Those 2 projections (probably; I haven’t checked this image) aren’t sufficient to reconstruct the image, but they already add significant constraints. For example, those 5 X-es in the next to last row can’t be in the first or last column (if they were there, the first image would start or end with a non-zero value) The more projections you add at other than orthogonal angles, the more constrained the solutions become.