How to extract graph from microscope image?

Question

I have a microscope image of actin filaments and I'd like to extract the geometry of the bright lines into a Graph object:

Here's what I have so far, using the above image as img:

s1 = MaxDetect@
   LocalAdaptiveBinarize[img, 8, PerformanceGoal -> "Quality"];
s2 = MaxDetect[s1];
s3 = TopHatTransform[s2, 0.74];
s4 = DeleteSmallComponents[s2 - s3];
HighlightImage[img, s4]

But this misses lots of lines and the output isn't really a skeleton.

Here are a few more example images of the cytoskeleton to try this on:

example1 = CloudGet["https://www.wolframcloud.com/objects/defc77bb-8218-4660-9fb2-d851c1145cae"]
example2 = CloudGet["https://www.wolframcloud.com/objects/b44045ec-f7ce-4db0-82bf-57e86d1967ac"]

Answer 1

Sorry for being late at the party, I hope it is still relevant. This is what I would do:

Setting your image as img I first equalize the brightness with BrightnessEqualize, then Sharpen the image, followed by some slight Blur, Erosion and a RidgeFilter that should bring us quite close to where you want to go

beq = BrightnessEqualize[img, {"Marginal", 2}]

sh = Sharpen[beq, 10]
bl = Blur[sh, 1];
er = Erosion[bl, 1];
rid = RidgeFilter[er, 2] // ImageAdjust;

Finally a LocalAdaptiveBinarize and a Thinning will give you what I hope is what you are looking for

lab = LocalAdaptiveBinarize[rid, 1]

Thinning[lab]

Optional:

If the First Local Adaptive Binarization step is giving you lines that are too thick, but the thinning backbone is too thin for what you need, you can perform a couple more Local Abdaptive Binarization followed by by blur, erosion, ridge filtering, sharpening... etc to get thinner lines

bin2 = ImageAdjust[lab~Blur~1~RidgeFilter~1] // Sharpen // Binarize

bin3 = ImageAdjust[bin2~Blur~2~Erosion~1~RidgeFilter~1] // Sharpen // 

Binarize

Finally you can also create a Vectorized version of all your results using ImageGraphics

I Hope it helps.

Answer 2

This is too big for a comment, but I wouldn't consider it an answer, more of a suggestion or partial answer. I don't have any solid expertise in this area, but it seems to me like if you want to highlight these lines, you might want to do some edge detection. For example:

s1 = LocalAdaptiveBinarize[
 EdgeDetect[img, 2, 0.0275, Method -> "Sobel"],
 100, PerformanceGoal -> "Quality"
];
HighlightImage[img, s1]

I'm not sure what it is we want to see, but to my eye this might be a step in the right direction at least. (?)

Also, I don't want to be "that guy," but are there higher resolution versions of these images? I might be wrong because this isn't exactly my wheelhouse, but I get the feeling it might be partially attributable to the fuzziness of the image, everything sort of glows and blends in, which might be less of an issue in a higher resolution image.