How to use do Sobel, dilation at image processing

I've conducted with the refrigerant of the evaporator visualization experiment, and proceeding image analysis after filming it.

the refrigerant pipe is round with 8mm diameter, want to know how much of liquid refrigerant flows.

Firstly, tried with binarize and threshold but couldnt get any satisfying result.

This result was not helpful, the original image would be rather intuitive than this.

And then asked for help and got some reply about using Sobel and canny filter.

He gave me real kind answer and reply. Also the sobel method he told me was pretty buch better than i did

This guy said this result was obtained by using Sobel -> Dilation(X2) -> Color Levels (in Gimp)

But didnt attach any codes or more explanations, Having problem with following his way,

Want to know how he did it, what the gimp is and get some code with this Sobel, Dilation, Color levels.

Will be really appreciate it for you guy's help.

Answer 1

[darova]

Try imgradient

I0 = imread('image.png');
I1 = rgb2gray(I0);
[gmag,gdir] = imgradient(I1);
I2 = uint8(gmag);
imshow(I2)