what can be the value of structuring element for dilating and erosion of size 256*256 pixels

I need to dilate and erode of image of size 256*256 so I need best structuring element value

[David Young]

The choice depends on more that the size of the image. In fact, it probably does not depend on the size of the image. So you may need to supply more information to get a good answer, including:

• What you mean by "best", stated with as much precision as possible.
• What the characteristics of the images are, with as much detail as possible.
• An example image, which you can attach to the question.

It will be best to edit your question to include this information - don't put it in an answer or comment.