I'm trying to take an image that consists of several noisy ellipses and use ListContourPlot to generate a contour of the image. However, I'm just getting a single dense line. If I binarize the image I get the correct result, but I lose the detail needed for the contour to be good. However, if I use Posterization with a value of two, it also doesn't work. What is Binarize doing that Posterize isn't, and why does ListContourPlot work with one but not the other?

Sidenotes: I've looked at the image data and the background of the image even before Posterization is mostly true black.

Contours also work with DistanceTransform.


FN = DialogInput[{filename = temp}, 
   Column[{"Browse for your file:", 
     InputField[Dynamic[filename], String, 
      FieldHint -> "Enter your file name"], 
     FileNameSetter[Dynamic[filename], "Open", 
      Method -> "Preemptive"], 
img = Import[FN];
img = ColorConvert[img, "Grayscale"];
(*img = ChanVeseBinarize[img]*)
img = ImageEffect[img, {"Posterization", 2}]
pic2 = ListContourPlot[ImageData[img, DataReversed -> True], 
   ContourShading -> None, Frame -> False, ContourStyle -> Yellow];

Show[img, pic2]

Image In: The source image

Image Output: The output image

  • $\begingroup$ Your image has an alpha channel that you should remove. $\endgroup$
    – chuy
    Nov 27, 2017 at 18:44
  • $\begingroup$ You can do this first: ColorConvert[RemoveAlphaChannel@img, "Grayscale"]. $\endgroup$
    – chuy
    Nov 27, 2017 at 18:49

1 Answer 1


With chuys hint:

img = Import["https://i.stack.imgur.com/vkvMu.png"]

imggray = ColorConvert[RemoveAlphaChannel@img, "Grayscale"]

colTable = {Black, Blue, Green, Yellow, Red}; 

contour = ListContourPlot[ImageData[imggray, DataReversed -> True], 
            ColorFunction -> (Blend[colTable, #] &), AspectRatio -> Automatic, 
            ImageSize -> Medium]

enter image description here

  • $\begingroup$ This worked! Also, I can use posterization to change the density of the contours. $\endgroup$ Dec 4, 2017 at 18:09

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