Levels & Curves – Input & Output Tonal Levels

Part of a new blog series

“All About Image Tonal & Color Contrast for Photographers”


The past several posts looked at L&C vis-à-vis color shifts

Today’s post looks at tonal effects (brightness)

For that, we’ll switch to grayscale

Easier to illustrate & see what’s happening


_DSC4327_nx_pwp filter sub 81ef-90-102_edited-1

Simulated Fog

Done using the contrast reduction method described in this post

See Figure 3


Shown below for comparison with the above is the

1. Fog using the Nik Collection’s Fog Filter

2. The Original Image

7-10-2013 5-39-33 PM

Since reduced contrast is what sets foggy scenes apart from normal (non-foggy) images

It stood to reason (to me anyway) that this method should work

Add it to your bag of tricks

I used the contrast-adjustment-only method shown in Figure 3 to make the featured image

The result (not shown) is even better when the combination method shown in Figure 4 is used

Try it yourself


The What – Two fundamental L&C functions (color and B&W both)

1. Setting B&W points

2. Controlling tonal contrast


The Why – B&W points and tonal contrast have a

Dramatic impact on images

It’s important to know how to adjust these parameters

L&C is just one way, but

It may be the most powerful overall


The How

The black & white sliders at the bottom of L&C

Can be used to set Black & White points

Moving the L&C “curve” end points up & down

Changes contrast

Both sets of operations are typically done together


Setting B&W points

When the black point slider is moved right

Every input tone in the image

Darker than the slider’s position

Is rendered black on output

When the white point slider is moved left

Every input tone lighter than the slider’s position

Is rendered white on output

This is shown in Figure 1

The cross-hatched areas are pure white & black

Every input tone darker than ~25 (0-255 scale)

is black on output

Every input tone lighter than ~229 becomes white


Lots of useful detail visible only if enlarged

Applies to this & all subsequent screen captures

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Figure 1

In the same vein, Figure 2 show the result of

Pushing the black point even further to the right

Note that besides more tones being rendered black

The remaining non-black and non-white tones

Don’t remain at their original tonal values

They get darker

7-10-2013 1-10-20 PM

Figure 2


Adjusting (global) Contrast

Here we look at changing contrast globally, that is

Throughout an image’s entire tonal range (0-255)

The next post will examine changing contrast locally

The final figure in this post is a preview of that

We just finished with the sliders at the bottom of L&C

Moving things vertically opens a whole new world

While B&W sliders defined which input tones are black

0 to ~25 in Figure 1

and which are white

~229 to 255 in Figure 1

The vertical adjustments define

What tone do we want to use for black output

o in Figure 1

& what tone for white output

255 in Figure 1

In the extreme, in an earlier post on negatives,

Dark inputs were turned to light on output and

Light inputs to dark

The very definition of a negative

Figures 3a & 3b show something less extreme

Resulting in a reduction of image contrast

Used to make the feature image “foggy”

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Figure 3a

3b is the same as 3a – without the cross hatching

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Figure 3b

Using this approach works well for reducing contrast

It’s useless for increasing contrast

(tune in to the next post for increasing contrast)


Then, of course, all of the above can be used in combination if desired

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Figure 4


Here’s a tease for the next post when

We move on to the Curves part of L&C

Curves represent the true power of L&C

Any & everything shown thus far in the L&C posts

Can be done with curves, plus

Much, much more

7-10-2013 1-37-26 PM

Figure 5


That’s today’s 500 (+100, oops) words

Continued tomorrow


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