Digital Zone System, Part 4 – Human Vision

The Zone System is all about

Getting the Tonal Contrast You Want

This is all well & good except

Sometimes what you think your eyes see

Is not accurate

Your brain fools you


It’s a problem if you’re trying to affect tonal contrast

and what you think you see isn’t what’s really there

Quick – Which Ellipse is the Lightest?

How would you make the tonal value of each the same?

What if I told you they are all Zone 10 – pure white?

They are all the same – pure white!

Your eyes are seeing pure white, but your brain says otherwise


This section will be repeated in each part of this series –
A useful reference
At the heart of the zone system is the zone scale which divides the tonal space from black to white into eleven zones.

Above & below – Wikipedia

There’s often a “gotcha” when it comes to

Getting the tonal contrast you want

That gotcha’s the human vision system

There is often a big difference between

The visual data captured by your eyes &

How your brain interprets that data

It’s the stuff that optical illusions are made of….

This can be a problem when judging tonal values IF

During capture and|or post-processing

Your eye (brain) is deceiving you

What can be done about it?

Capture – take lots of pictures and train yourself to See

Post-processing – Use a program like Silver Efex Pro 2 that can display tonal regions

I’ll describe SEP2’s zone system features in a future post

As a preview, here’s SEP2 showing zone 10 areas for the ellipse image

As I said, all three ellipses are pure white

Your eye is fooled because of the surrounding tones which range from pure black to pure white

Note pure white in upper left background tone

Bottom right is pure black

This problem holds for color, too, not just B&W

Click to enlarge for details

11-30-2012 7-25-54 AM

For the PS literate, you can verify the tonal equality by using the color selection eye-dropper to test & compare the ellipses.

Just for fun, here’s another example of the same visual perception problem. The question is which of the three smaller squares is the darkest?

After the three ellipses you’re probably tempted to say – they’re all the same (regardless of what your eyes|brain say).

You’d be right. It’s another example of perceived tonal values being affected by the tonal values of the surrounding area.

This can be verified in the same way as suggested previously for the ellipses – test via SEP2 or PS, for example.

Or – just trust me 😉

There’s a second “illusion” present here as well for the visually acute.

Look at the large square in the center.

Doesn’t its left side appear to be lighter that the right side?

Same phenomena again

For both color and tone there can be quite a difference between true and apparent (perceived) values.

More tomorrow – keep shooting & train yourself to see tonality.

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0 thoughts on “Digital Zone System, Part 4 – Human Vision”

    • Thanks. Trying to go a few steps beyond snapshot point & shooting just to give those bored with the same-old-thing something to think about – or not. 😉

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