Exercise: Colours into tones in black and white

The original image in colour for this exercise:

Camera body: Nikon d90

Lens: Nikkor 18-55mm f/3,5-5,6

f/11   1/60 s   ISO 1000

Focal length: 24 mm

I used a still life with contrasting colours but I didn't have any grey card so I used a grey cardboard box.

Then I converted into a B&W image in Photoshop:

Grayscale

Red filter

Yellow filter

Green filter

Blue fllter

I made the same thing in Lightroom because I wanted to check if there is any difference between the preset filters.

Grayscale

Red filter

Yellow filter

Green filter

Blue filter

If we apply any of the colour filters in B&W we make the colour of the filter middle grey. 

Red filter makes the red ruler middle grey, and its complementary, the green, nearly the same but the yellow and orange brighter and blue and purple dark grey. 

Yellow filter darkens the blue while the rest colours are brighter.

Green filter gives to red and green colours same brightness and it's the filter which reflects better the brightness as it is in my opinion.

In the blue filter, the blue stapler is middle grey and its complementary, the orange colour looks black and the yellow and red are also darker, but purple is brighter.

There are some differences between the filter presets in Photoshop or Lightroom. The main differences are noticed in Red and Yellow filters, in Photoshop yellow and orange colour appear as white without detail, much brighter than the background which is white!

The other difference is with blue filter. In photoshop the filters darkens much more the yellow colour and we can't notice the difference between the yellow and orange in the flower while that difference is clear with Lightroom's blue filter. And even the overall image is darker in Photoshop.