Levels & Curves – Color Shifts & Changes

Part of a new blog series

“All About Image Tonal & Color Contrast for Photographers”

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Applying L&C adjustments to individual channels

Can provide interesting (& surprising) effects

Demonstrated via somewhat extreme examples

(to vividly illustrate the point)

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Floral Rainbow

Shot through a piece of  textured glass

No adjustments; just the glass

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The What – Illustrations of  L&C color impacts

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The Why – If we use L&C to change

Black and|or White Point settings, and|or Contrast

It will cause color shifts and other color changes

by changing Hue & Saturation & Brightness

Unless changes are made only to the Luminosity channel

In which case only Brightness is affected and

Hue and Saturation are unchanged

The illustrated examples below help to clarify

Basic color parameters (hue, saturation, brightness – HSB) and

How changes to one parameter affect the others

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The How – The two previous L&C posts showed the effect of changing

The three sliders at the bottom of L&C

Alters Black, Mid-tone & White points

The two end points of the actual “curve” in L&C

A negative of an image (both color and B&W)

(when moved to the two extremes)

Let’s take a closer (and final) look at the impact of

Moving the curve’s end points

The practical benefit of this illustration is

A better understanding of colors and

What an editing program’s color models are telling you

(should you choose to listen 😉 )

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Let’s begin by repeating an earlier example

A fairly extreme color change – turning positives to negatives

I’d suggest enlarging this & looking at it closely

Especially note the RGB & HSB values

These values & the changes show everything

One needs to know to understand what comes next

That “understanding” is up to you

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Next – here’s what happens if we do the same adjustment except

Only to the Red channel

Compare it closely with the result above

Surprised by the change of Red to Black?

 (& its inverse, Cyan, to white)?

(& a bunch of other changes)

Can you explain it? You should be able to

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The answer is in understanding  H/S/B color models

If the H/S/B value of B (brightness) is zero

The resulting color is black regardless of  H & S

And it’s white if  B=100 AND  S=0, regardless of H

A “pure color”, as shown in the chart is (H/100/100)

For any H as long as S=100 and B=100

Inverting Red (H/S/B = 360/100/100)

Makes B=0 (or black)

Since anything Red is now black,

Red’s inverse, Cyan, must be White

Easy-peasy once you study color models & think about it

You’re on your own past this point

32 possible channel combinations for you to explore

RGB, R, G, B, Luminosity

I’ll show one more –  RGB + Red (the combination of the above two)

The other 29 are left to the interested reader

Without looking ahead (it’s at the bottom of the post)

Can you predict what happens when we

Invert the RGB channel? and the Red channel??

Both at the same time???

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For convenience,  here is the entire progression

The H/S/B explanation following the previous example

Tells all there is to know in order to understand this

Click to enlarge

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In addition to considering the Red & Cyan changes to B&W

Also look at the changes to the original B&W top|bottom borders

The result is exactly what was predicted if

You looked at the very first (RGB channel) example in the post

Colors flipped vertically (incl. in the top/bottom borders)

When adding RGB inversion to Red only

You should begin to see a pattern developing

And be able to predict what will happen when you

Do this with the Green channel (instead of the Red)

(In your own tests right after reading this post 😉 )

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That’s today’s 500 words

Continued tomorrow

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2 thoughts on “Levels & Curves – Color Shifts & Changes

  1. Invert RGB & Red = invert RGB & Blue & Red & Blue = invert GB Intentionally confusing our readers, are we? 😉

    BTW, I think trying to understand the color changes in the additive RGB model is easier than in the HSV model. At least for me.

    • I doubt if more than a handful of readers got this far so probably very few got confused. 😉 . Readership (views) fall way off with posts that get to this level of detail. For the rest of us, just a few thought puzzles or “hmm, that’s interesting”.

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