Concept
Using Gradient map can be another way to get grayscale
photograph. But you need to keep black and white color for background
and foreground.
1. Open an image to for grayscale output. Make sure
that Black and White color are kept as foreground and background
colors else press "D" to get the required result.

2. Image > Adjustments
> Gradient Map
3. Click OK
.
4. You will get the following output.

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