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”

 SINCE CONTRAST IS DUE TO DIFFERENCES IN TONES

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

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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 –

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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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