How to brighten background only?

[monicaross]

Hello! Any tips on how to brighten the background only in a portrait? I have tried several techniques but it has ended up choppy each time. Thanks in advance!

[PixLab]

Can we have the picture?
There are so many ways to select a background, but it all depend about the picture.

[Ofnuts]

A technique is to use an advance version of  Luminosity masks.

• Duplicate your layer and de-saturate it. Start Curves on the result. Try to locate the tonal range of the background: here, by clicking on the background curves adds the line at x=111 so the background is likely bump in the histogram around that value.
  

   

• Create a bell-shaped curve that encompasses these values. The background should turn very white.
  

   

• Open the Channels list, right click any of the R/G/B channels and Channel to selection. The selection level of pixels will now be related to their proximity to the tonal range of the background.  
  
• Hide/remove the de-saturated layer
  
• Hide the selection marker (marching ants)
  
• Activate the initial image layer and start your color tool again (here I use Curves, but you can use Levels, Brightness/Contrast, Saturation...). Note that here the histogram is weighted  by the selection level so the extremes (that are not selected at all) are not included.
  

   

As you can see there are no hard transitions:

   

If the background has a color that is different from the rest (for instance vegetation that is mostly green) you can take advantage of this in the de-saturation step. Instead of doing just a de-saturation, use Colors ➤ Mono mixer to start with a desaturated image where your background is boosted (in the simplest case you can just copy on of the R/G/B channels).

[denzjos]

@Ofnuts, nice tutorial. Very useful (but little panic here, I thought my cat has run away )

[Ofnuts]

(09-03-2021, 09:04 AM)denzjos Wrote: @Ofnuts, nice tutorial. Very useful (but little panic here, I thought my cat has run away )

Definitely mine (or more accurately my son's) and i have scars to prove it (and so does my favorite armchair...). Pixel, Pixou, Colonel Pattoons, "Ce p... de chat" (he has many names) has claws that are even sharper than my DSLR lenses.