How to maintain graph style in HighlightImage?

Question

Highlighting an image with a graph seems to change the styles of the graph vertices:

img = CloudGet[CloudObject[
  "https://www.wolframcloud.com/objects/f28eb939-485b-4899-8ff7-e6c7d64cef60"]]
mg = MorphologicalGraph[
   DeleteSmallComponents[Binarize[RidgeFilter[img, 3.5]], 20.7], 
   VertexSize -> 7, VertexStyle -> Yellow,
   EdgeStyle -> Directive[Red, Thickness[0.01]], ImageSize -> Large];
Row[{mg, HighlightImage[img, {Show@mg}, ImageSize -> Large]}]

Is there any way to prevent that?

Answer 1

Your code is fine and the style is preserved, but the edges are actually not completely opaque which makes them darker when the black of the image is in the background. Try something like this

mg = MorphologicalGraph[
   DeleteSmallComponents[Binarize[RidgeFilter[img, 3.5]], 20.7], 
   VertexSize -> 7, 
   VertexStyle -> Directive[Opacity[1, Yellow], 
     EdgeForm[Directive[Thickness[0.002], Opacity[1, Red]]]], 
   EdgeStyle -> Directive[Red, Thickness[0.01]], ImageSize -> Large];
HighlightImage[img, Show@mg, ImageSize -> Large]