Adjusting the amount of white or black in a hue to match a complementary color?

[southwestform]

I want to take photos of people with studio lighting against different colored backgrounds. Perhaps the subject will be wearing a green dress and be photographed against a pink background creating a complementary color scheme. The amount of white and black in the dress and background will not always be a close match. How could I use Photoshop to select either the dress or the background, the background will probably be easier, to adjust it so it matches the amount of whites/blacks/brightness/vividness of the other? Is this just trial and error OR is there a more precise way of doing this?

Thanks in advance!

[Norman Sanders]

One way to match subject-to-backgound luminosity percent of whites and blacks in the image without affecting the color is to switch to Lab Color mode and adjust ONLY the  L channel. Mask out the subject.

Use the Color Sampler tool to mark the white and black aim points in the subject. Their values will appear in the Info Panel. Then mark the white and black aim points in the background. Place the background aim points on the Curve. Use Curves and the north/south keyboard arrow keys to adjust the background aim point values displayed in the Info Panel to match the subject values.  

[southwestform]

1. Do you mean to switch the color mode of the entire image to Lab under Image > Color Mode?

2. Using the Color Sampler, I should pick two points? I should pick what  seems to be the brightest part and the darkest part In the subject?

3. I should repeat step 2 for the background?

4. What is the purpose of masking out the subject?

Thanks!

[Norman Sanders]

southwestform  Jul 25, 2018 4:54 PM (in response to norman sanders)

1. Do you mean to switch the color mode of the entire image to Lab under Image > Color Mode?

Yes. Change the Mode to Lab Color.  You will switch back to RGB after the work is done.

2. Using the Color Sampler, I should pick two points? I should pick what  seems to be the brightest part and the darkest part In the subject?

Yes, you will pick the two points -- the luminance values you want to be alike in the subject and in the background area. That is what you said is your goal.
You will pick a total of four values:

     Two values in the subject, the person, (black and white) that you like. Call them Subject Values.. The luminosity extremes or near luminosity extremes are a logical choice but that is not a must.

     Two values in the backgound area that you will want to change to match the Subject Values.

3. I should repeat step 2 for the background?

If you mean should you mark the values you want to change (the background area values, yes. Those two values will later be placed on the Curve.

4. What is the purpose of masking out the subject?

By masking out the subject, when you change the Curve to adjust the background values it does not affect the subject values. In order for this to be possible, all your work will be on a duplicate (Cmd+J) of the background layer layer, which also holds the mask. The subject values will then be displayed from the bottom layer.

If you post a sample image here with your chosen white and black aim points in the subject and the background area we could give you instructions that will include marking and moving the value of those points on the Curve. (I assume you know how to make a mask of the subject so we may not provide information on that.)

One more thing: Be aware that changing those background area values will also affect luminosity throughout the range. The degree of change depends upon the amount difference from the current pair of values. It may be insignificant. It may not. That is the reason for us to have a sample image.

[JJMack]

I would think it would be relative easy to select the background. Then add some kind of an adjustment layer with the selection active to adjust the background to your liking. For example a Hue and Saturation adjustment layer. Get the subject to what you want then adjust the background.