Contrast Part 8: Levels & Curves – Refining Adjustments

The same post-processing adjustment is rarely needed in equal-measure over 100% of an image. Ways to apply adjustments selectively are needed. This post looks at ways to apply the levels portion of the Levels & Curves tool in a selective manner (curves in the next post).

 Part 8 of a series

“All About Image Contrast for Photographers”


Every part of an image

This post examines

Ways to selectively apply tonal adjustments

Using the Levels portion of Levels & Curves

(In general, this will also apply to Curves – a future post)

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Levels Tonal Adjustment

<<Before | After>>

Adjustments made at the channel level; read on

The What – Application of Levels’ adjustments to

All three color channels, R/G/B, at once or

Individual color channels alone or

Just the Luminosity channel or

Any & all combinations of the above


The Why – Global  tonal adjustments aren’t always desirable

Color casts or shifts may be an issue

A pre-existing cast you wish to remove

Saturation shifts may occur

When tonal adjustments are applied across the board

The How

Use the L&C Channel selection menu to choose among

RGB (global)

R or G or B individually

Luminosity (hue & saturation remain unchanged)


Black point shift applied to RGB

Click any of the following images to enlarge

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Black point shift applied to red channel

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Black point shift applied to green channel

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Black point shift applied to blue channel

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Black point shift applied to RGB (left)

and to luminosity channel (right)

Note the color change with RGB

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Mid-tone shift applied to RGB

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Mid-tone shift applied to luminosity channel

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Mid-tone shift applied to red channel

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Mid-tone shift applied to green channel

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Mid-tone shift applied to blue channel

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Shift of all three sliders applied to luminosity channel

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Shift of all three sliders applied to RGB channel

There’s that color shift in the daisy’s center

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The Luminosity channel is better than RGB in many cases

This is because applying tonal adjustments to

All three channels (RGB) simultaneously

Can cause unwanted color changes/shifts

Changing only Luminosity

Leaves hue and saturation unchanged

A practical example – removing a color cast

There are many ways to remove a color cast

Levels may not be the best (depends)

Here’s a Before image with a green cast (left) and

After – using red & green channel adjustments

Increase red & decrease green via mid-tone slider

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The same can be done without

Using the green channel (see next image)

This red/blue adjust (ignoring green altogether)

Is in line with how

Many “built-in” White Balance tools work

They set WB by adjusting ONLY Red & Blue

Green is reduced by raising both

vice versa to increase

Red cast removal = less red & more blue

Blue cast removal = you can guess….

Changing (adjusting) colors on a per channel basis

Requires familiarity with how colors mix

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