Nonzero pixels in black image?!

In an image process, I have got an image which after being inverted (to calculate the perimeter), it becomes absolutely black on screen. But when I see the pixel values, the last row and column are not zero!

why?

I mean when you sum the pixels, it is not zero!, while the image is completely black!

Thanks!

Steven

Answer 1

[Walter Roberson]

Your display is not set up to display a color that dark notably differently than true black. This is proper behaviour. Remember, a pixel value of 1 (out of 255) is not very bright.

[Steven]

Thanks Walter.

But I forgot to mention that the image is a binary one! So when it is black, all the pixels must be 0, right? but here I have got (exactly!) the last row and column WHITE! Why?

[Image Analyst]

Use imwrite to save your binary image and then post it.

[Walter Roberson]

What is class() of the data ? If it is not "logical" then there are non-zero values that are dark.