Justify captions in figure floats

[Påvel Nicklasson]

Is it posible to justify the width of some captions in a book project to  
the width of the figure?
The book has two columns. All figures are placed inside floats. Some  
figures are wide and span columns, but do not entirely fill the text  
width. With the standard settings captions fill the text width, even if  
the figure doesn’t. I think it would look better in these cases if the  
caption had the same width as the figure.

I have looked on the Floatrow package but is seemed very complicated. If  
it is possible to achieve some examples would be appreciated!