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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Contrast Part 7: Levels & Curves – All about LEVELS

A previous post provided an overview of the Levels & Curves tool, one that you should be proficient with if your goal is an exceptional image. The tool’s name has two parts – because it provides two functions. Today we’ll look at LEVELS.

Part 7 of a series

“All About Image Contrast for Photographers”


Part 6 illustrated what the L&C display tells us

Today’s post will examine

The Levels portion of Levels & Curves

The Curves portion will be in a future post

D300_130701_164218__DSC7206 lr5acr l&c feature 1

Levels Adjusted

Capture > RAW Conversion > Adjust Tones with Levels

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The What – The Levels Components of  Levels & Curves

One of the most fundamental and useful tools

For adjusting image tonal (brightness) values

Available in any image editing software that’s worth using

The Why – Most images benefit from tonal adjustments

As they come from the camera, the are often flat (lack contrast)

The How – We’ll look at Levels, a part of Levels & Curves

Levels adjustments are made using 3 sliders shown in Fig. 1

1. Slide the black point slider to the right to darken

Any pixel with tonal value darker than the slider’s position

Is rendered black

2. Slide the white point slider to the left to lighten

Any pixel with tonal value lighter than the slider’s position

Is rendered white

3. Sliding the mid-tone slider to the right darkens

To the left lightens

The three sliders can be used alone or in any combination

Click to enlarge; L&C is at upper right

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Fig. 1

The following 51-sec. video shows these sliders in action –

There’s a lot more to show about using Levels

Application to the entire image, vs.

Application specifically to individual color channels, vs.

Application to Luminosity without affecting color, vs.

Selective application (say, everything except the daisy’s center)

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All of these and more in upcoming posts

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Contrast ………………………… A Short Tonal-Measurement Detour

Contrast is all about tonal differences, in both color and brightness. Tonal adjustments require that we be able to measure what we (think) we see. We can’t depend our eyes since they often deceive us. What we think we see is not always the same as reality. That’s the reason behind optical illusions.

A wayside stop in series

“All About Image Contrast for Photographers”


Tools are needed to measure tonal levels

We can’t depend solely on our eyes (if at all)

So – before continuing with Levels & Curves

This is a short detour to examine one such tool

The Color-Picker

These tools vary from program to program

(where they even exist; search your programs)

but the principles are the same

D300_090622_105046__DSC7426_nx v2

Framed (by nature)

Before starting, Ed –

We can’t depend on our eyes to measure tones?

What’s that all about??

A simple illustration should answer that –

6-28-2013 7-42-14 AMFig. 1

You can prove to yourself that

The tones are identical (equal) across any individual strip

Read on to find out how

At this point you may be wondering why you should care

Since we view an image with our eyes.

That is our reality

Well – yes & no

Setting black & white points is a future topic

The above illusion can cause you to misread

Where the darkest & lightest points are in an image

This will affect your B&W-point settings

Your choice, but be an informed user when deciding

A tool to measure tonal values (& more) – the Color-Picker

If you’re not using some version of PS, including Elements,

Search around in your programs for a color-picker-like tool

Photoshop Elements will be used here


“Picking Colors” Step by step

  1. Click on the foreground/background color tool

By default, located at the bottom of PSE’s toolbar

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  1. This opens the Color Picker window

We’re interested in the H/S/B & R/G/B values

(on the right side)

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  1. Moving the cursor (arrow) from the C-P window

Changes it to an eye-dropper

Note that the values of interest haven’t changed

Not until you click on  the image

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  1. Click somewhere on your image

Note the values –

Since the image is a grayscale chart

R=G=B (=102 in this case)

Is what we should expect

since R=G=B is the requirement for gray

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  1. Putting it all together, the next screen shot illustrates

That our optical illusion is just that, an illusion

The tonal levels are identical on both sides of the test strip

Check it out for yourself; don’t take my word for it ;-)

Click to enlarge

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The C-P isn’t limited to grayscale and its 256 possible tonal values

More like all of the possible R/G/B combinations –

16,777,216 to be exact (including the 256 grays)

Give it a try; explore the world of colors and tones

Click to enlarge

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Levels and Curves at the Extreme

Before continuing further into Levels & Curves details let’s look at an example of what this tool makes possible – arty contrast extremes. This is a “tease” for the next few Levels & Curves posts.

Part of a series

“All About Image Contrast for Photographers”

Contrast Extremes

_DSC1533_316_nx wbdl sep1

Extreme Black & White


Refer to yesterday’s Levels & Curves post

To compare this image’s settings with the default settings

Click for full screen

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We are essentially asking that all input tonal levels

Darker than a certain point be changed to black, and

Lighter than another point be made white

A very narrow tonal band (the width of the sloped line)

Will be a dark gray

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In effect – a black and white (no tones of gray) image

Surprisingly (or not) the subjects are easily recognizable

I have this saved as a Silver Efex Pro custom preset

The exact locations of the black range & white range

May need tweaked depending on the input image’s tones

But not very much

This is a “tease” for the next few Levels & Curves posts

Try this on your own

It’s hard to learn by just reading (with no experimentation)

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Contrast Part 6: ………………… Levels and Curves, 101

The Levels & Curves tool is found in almost every post-processing program. Its ubiquitousness  is with good reason – it’s the single most powerful post-processing tool. Learn it well and you can accomplish almost any tonal & color contrast adjustments.

Part 6 of a series

“All About Image Contrast for Photographers”


No other contrast adjustment tool is its equal

We have lots of post-processing programs to choose from

and they all offer different contrast adjustment features



Level and Curves is the common denominator

It is the one contrast adjustment tool that

All good post-processing programs share in common

A perfect place to begin our journey

(and it doesn’t hurt that it’s the most powerful, also)

D800E_130514_094430__DSC8652 acr cep-1

Calla Lily

(iPad camera & Snapseed)

Today’s post is only about L&C basic principles

Apologies to those for whom it’s way too basic

I’ve found over & over that

Assuming everyone knows something or another

Is a bad assumption when explaining anything

Go grab a cup of coffee & stop back tomorrow ;-)

I’ll use the Levels & Curves from Color Efex Pro

Other programs’ L&C are similar

All operate on the same basic principles

In a later post, I’ll examine a few program specific implementations


If you were to  open L&C in Color Efex Pro you’d see this

We’re interested in the contents of the red rectangle

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Fig. 1

Begin by ignoring everything except the numbers in red

It’s essential to understand what they tell us

In the simplest sense when you see

0 – think black

255 – think white

A number in between – think shades of gray

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Fig. 2

Those numbers are showing you tonal levels

In comparing their meaning to that of the more familiar histogram

The axis labeled INPUT is identical in meaning to the histogram’s

It’s the tonal levels of the input image’s pixels

The axis labeled OUTPUT is totally different

A histogram Y-axis measures pixel count

How many input pixels have a tonal value of 0,

How many 2, 3, 4, …., 255?

In the L&C display the Y-axis shows us the

Output tonal level for

Pixels with a given input tonal level

As an example, in the default L&C, shown in Fig 2.

Output tonal levels are identical to input levels

That is – the image is unchanged

128 in gives us 128 out (middle gray)

0 in, 0 out; 255 in, 255 out

Base on the above, let’s see how things change if we

Change L&C’s default settings

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Fig. 3

By the numbers –

1. Change the dark-side from

0 In & 0 Out to

0 In & approximately 50 Out

This means a black tonal input level (0) is now

Gray with a tonal level of 50 when it’s output

Further, the new “curve”, the diagonal white line,

Differs  from the default (red)

Everywhere (except at 255, 255)

This says that every input tonal level

Is now lighter when it is output

2. The above changes are reflected in the histogram

Note how far the darkest area has shifted

Further, the entire histogram is compressed


The wider the histogram, the greater the contrast

This simple change greatly reduced the image’s contrast

3. Shows the visual effect of 1 & 2

The above tells how I made this before|after shown yesterday

Raised the 0 end as shown AND dropped the 255 end

6-26-2013 9-10-43 AM

500 word cut off – see you tomorrow ;-)

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Contrast Part 5: ………………… Contrast Adjustment Basics

The series’ previous posts illustrated both color and tonal contrast and explained their importance. Today’s post is step-one in showing how contrast can be adjusted.

Part 5 of a series

“All About Image Contrast for Photographers”


Photoshop, Lightroom, Aperture, GIMP, .. the list goes on

The number of contrast adjustment options is even greater

This post introduces the grand-daddy of

All contrast adjustment tools (& the most powerful)

Subsequent posts will elaborate and

Discuss other members of granddad’s family



Walking the dog in the late afternoon

Saw this enormous cloud

Ran back inside, grabbed the D800E with 70-200 f/2.8 & tripod

Took this shot (the cloud already had lost some of its “punch”)

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Alfred Stieglitz, a famous photographer,

Made a series of cloud photos (1925-31) which achieved fame

I have to admit that I don’t get it

To recap the message of this series’ earlier posts –

There are two basic types of image contrast

Tonal & Color

Each has a different impact on the human vision system

Proper contrast is important for

Image impact (eye-catching vs. ho-hum)

Most  images need post-processing to achieve the best contrast

Straight-from-the-camera contrast is often flat

I plan to do the rest of this series,

The what, why, and how of Contrast Adjustment

In small bite-size pieces (500 words or less)
Maybe 10 or so bites

For the most part I’ll be using Figure 1 (all or pieces of it)

To illustrate the what/why/how

Download a copy and follow-along day-by-day

Reference Print printer 2362x3543pixel

Figure 1

Lesson #1 – The Hallmarks of High & Low Contrast

To begin, we need to recognize high & low contrast when we see it

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Figure 2

Figure 2 shows that the difference between high and low contrast

Manifests itself in two ways

Visually – image “Pops” (high) or it’s Flat (low)

“Pops” is a technical photography term ;-)

Histogram – Wide (high) or Narrow (low)

Ed, what is this “grand-daddy” of all contrast tools?

It’s Levels & Curves, or to be more precise

The Curves portion

This is a tool found in one form or another in

Any post-processing software that’s worth using

If you learn to use it,

There is virtually nothing than can’t be done contrast-wise

At least nothing important

Tomorrow, all you ever wanted to know about

Levels & Curves

If you downloaded Figure 1’s test image

It’s an exercise for the interested reader to

Do the high-to-low contrast conversion shown in Figure 2

The high is taken directly from Figure 1

The low was made using Levels & Curves

Easy; not rocket science

Time to go; word count is over 450

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Contrast Part 4: ………………… Luminosity and Lightness

Yesterday looked at describing and measuring color. Today we consider tones. When it comes to contrast, tones are where the magic is made in our images.

Part 4 of a  series

“All About Image Contrast for Photographers”

Just as contrast itself comes in several “flavors”

1. Tonal contrast

2. Color contrast

The same is true of lightness (brightness)

1. Measured by a device (light meter for example)

2. Perceived by a human’s vision system

Since brightness is “the stuff from which contrast is made

It’s important to understand how it is

Measured (and perceived)

If we want to control contrast in our images.

Imagine Monet at a green field of red poppies palette in hand

and you at his side with your camera

Click to enlarge

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Luminosity & Lightness

We need to know how to display lightness in its several forms

Further, we need to know how to adjust the resulting contrast

For example – how to get from #3 to #4, if we were Monet

(Being able to change 3 to 4 in post-processing is a key to making magic)

The significance of equiluminance was discussed in part 2

This painting by Monet was used as an example

Monet – Impression: Sunrise

Note the sun vs. its background

Wildly different hue, but


 In the next part –

How to adjust brightness

Both perceived and actual

(Ansel’s dodge & burn changes the perceived portion;

how can the actual be changed?)

Also, closely related, different B&W conversions, e.g.

The conversion that shows perceived lightness (grayscale)

Is not the one to display luminosity

(Hajo, This is related to our long series of comments in a recent post)

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