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Line and Edge Enhancement IV: Size Doesn't Matter

Updated: Apr 12, 2020

This is the fourth in a series of posts regarding the Chevreul Effect. This effect is extremely useful for understanding how our visual processing enhances perception. Reading these previous posts will increase your appreciation of this one.

A brief recap: We perceive a subjective brightness gradient when bands of differing objective luminance are placed next to one another. What we see is different than what a light meter would read. This is the Chevreul Effect. Because of this effect, our perception of line and edge is enhanced.

The Chevreul Effect

The Chevreul Effect changes dramatically when it is placed on a background luminance gradient. The two Chevreul diagrams below are identical but inverted.

The Chevreul Effect on a luminance gradient

In today's post I add another element to the first two. The above effects remain identical regardless of size:

The Chevreul Effect remains the same regardless of size

This is truly amazing if you imagine for a moment what it would take to engineer this. Our visual processing system has the ability to ‘localize local context’. Context can cover the entire field of vision, or be limited to a tiny location within our vision.

Context is everything when it comes to perception of edge, line, contour, detail, and brilliance. This remains true whether we are looking at a large scene or a tiny detail.

In the painting below, appreciate the brilliance of the girl's headdress, and the simultaneous detail in the man kneeling in the darkness.

Franz von DeFregger (1835-1921) Visitors in Tyrol

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