Identify the special area in low-contrast image

I am trying to make MATLAB recognize ellipse in the image, but no matter how I adjust the thresholds for imbinarize and imadjust, MATLAB cannot fully recognize it. Are there any other methods I can try?

original file is attached

[DGM]

Do you have more than the one example image? Knowing how the images vary might help with making the solution reliable.

[luo jingcheng]

yes, i have two more

[KALYAN ACHARJYA]

You can experiment with image filter or adjustment, followed by thresholding, and then proceed with a series of morphological steps. The precise steps for segmentation can be provided once I tried the initial process.

Answer 1

[Image Analyst]

Try activecontour

[luo jingcheng]

tried, the result wasn't very good

[Image Analyst]

Keep trying -- sometimes it's tricky to get all the options adjusted correctly.