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High Pass & Gaussian Blur Filters

Compared with Step Wedges

High & Low Frequency

Image Information

Photographs contain high and low frequency image information.

The High Frequency - Low Frequency Step Wedge below has:

• High frequency image information to the left.

• Low frequency image information to the right.

An example of high frequency information is the eyelashes on a portrait.

In the same portrait, the white of the eye below the eyelashes has low frequency information.

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High Frequency Image Information Low Frequency Image Information
Such as Eyelashes Such as the White of an Eye

High Frequency - Low Frequency Step Wedge

High Pass Filter v. Gaussian Blur Filter

The High Pass and Gaussian Blur filters do the opposite of each other.

The High Pass filter allows high frequency image information to pass through.

Low frequency image information is blocked.

In contrast, the Gaussian Blur filter is a low pass filter.

The filter allows low frequency image information to pass through.

High frequency image information, where there's lots of detail, is blocked.

Filter High Frequency Low Frequency
High Pass Passes Blocks
Gaussian Blur Blocks Passes

Below, compare the HL Step Wedge, the HL Step Wedge with High Pass Filter Applied, and the HL Step Wedge with Gaussian Blur Filter Applied.

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High Frequency Image Information Low Frequency Image Information

High Frequency - Low Frequency Step Wedge

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High Frequency Image Information Low Frequency Image Information

High Frequency - Low Frequency Step Wedge

With High Pass Filter Applied (Radius: 10 px)

High frequency image information (detail) is passed.

Low frequency image information (little detail) is blocked.

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High Frequency Image Information Low Frequency Image Information

High Frequency - Low Frequency Step Wedge

With Gaussian Blur Filter Applied

(Radius: 10 px)

High frequency image information (detail) is blocked.

Low frequency image information (little detail) is passed.