Contrast is key to make things visible. When using certain software, the black and white filter will be showing different variations is software. If an image has similar colours, then the objects within the object will all blend into one another.

Consider this image for example.

When we grayscale an image, it reveals the contrast between the different colours used in the image.

When we want to make a Black and White Filter, we need to set it to:

Red- 30%

Yellow- 89%

Green- 59%

Cyan- 70%

Blue- 11%

Magenta- 41%

Apply these colours and it will get out the true brightness of the black and whire image, and give a good idea of what your contrast is.