image processing - How to remove the noise without destroying the main edge?

I am working on a project. I want to segment a logo from a car and the picture's size is 3648*2432. The logo is selected by the red rectangle.

I extracted this area and turn into gray level. The area's size is 249*173. Then, I use histogram equalize to enhance the edge. Finally, I use adaptive canny to find edge.

However, the result is not perfect. So, I used median filter to smooth the left picture. The result is as following.

I remove the small parts.

The result has been improved, but it is also not good. Besides, I have tried bilateral filter, mean filter and Gaussian filter, but the result is not good, too. I know that after passing histogram equalize, the noise can be enhance. But, in some case, low contrast, I need to adapt this step to enhance my picture. Is any one who can provide me any different comment? Thank you very much.

Answer

Use bilateral filter or anisotropic diffusion first.

The effect of anisotropic diffusion is as the following:

. The MATLAB code can be found here.

Here is its effect on your image:

Finally, non-local means is a also a good way to get rid of the noise. You might also want to take a look into that. I warn you though, it is slow.