Today I introduce about how to change the background to black and white except main objects in a photo. First, open the photo that you want to edit.
go to Image>Adjustments>desaturate. Then photo will become to black and white.
Next, choose the History Brush Tool from tool bar in left side.
Use the brush to object that you want to use the colours. (like this↓)
Finish! The elephant is very colourful, but background is black and white. 
We can change the photo from this stage for example use different filters.
Photoshop can edit the photos very easily.
Saran Kim | Blog 