Why does decreasing exposure desaturate an image?

[willdoak]

Sometimes I try to decrease highlights on skin using the adjustment brush and decreasing the exposure. That not only decreases the exposure, but desaturates the skin. I end up with gray patches rather than less-bright skin tones.

Cheers,

Will

 

[Rose Weir]

Do a search for George Jardine's blog (website) he has a series of video tutorials but the sample one that can be downloaded by request illustrates methods to use for your situation.
Basically Jardine says to avoid that 'grey patch' look balance the -highlight adjustment with a little + exposure....I also find -highlight with + shadows brush works. The flow of the brush is of importance as well...as in most things less is better than more.
In the sample video (he has a series that can be purchased and they are worth the 25.00) he corrects a white backlit beard...demonstrating the - highlight and how the +exposure on the same brush balances out that 'grey' result that can occur

Rose

 

[willdoak]

Thanks. I'm working through the Jardine videos now.

Will