Need correct detection of countours

I am detecting the countours but some dark regions of the image are not detected and therefore area of the countour is not accurate.

please guide me for the same. Thanks in advance.

[KALYAN ACHARJYA]

Please do share the sample image with more clarification

[swati mane]

Thank you for your reply sir.

Please find an attachment.

For this image i have detected blobs and countours but for the dark (black) regions of vehicles , for example, window or front glasses of vehicles , I am not getting the correct blob area.