Binary image have white pixels after a Gradient In

[ispbarum]

When I process an image in NI Vision Assistant version 8.5.0 using the following steps:
1  Original Image- <Vision Assistant>\Examples\metal1.jpg
2  Grayscale - Manual Threshold - Minimun 120
3  Binary -Basic Morphology - Gradient In (Structuring Element size 3x3, all sectors selected)
The resulting image shows several white pixels (grayscale intensity = 255)
Why the resulting image is not a binary image?

[muks]

you are right.I think it is showing single pixel gap alone.Just a guess.I tried varying the threshold but couldnt conclude on anything.

[muks]

Anyway nice observation

[ispbarum]

Vision Assistant version 8.6.0 has the same problem.

[ispbarum]

The NI Vision Concepts Manual says:

The internal edge subtracts the eroded image from its source image.

The remaining pixels correspond to the pixels eliminated by the erosion process.

If I is an image,

Internal edge (I) = I - erosion(I) = XOR (I, erosion (I))

Doing the operation I - erosion (I) do not appear white pixels, but using the Gradient In function the resulting image shows several white pixels.