Thursday, March 12, 2009

High Pass Filter

One of the comments on Chris' post on HDR had to do with the filters that were mentioned. Chris "the science guy" Russ often throws out terms thinking that everyone is one the same page. Unfortunately, some of us aren't even in the same book. :-)

Side note: the picture shown above was taken by an arson investigator. It was processed using the technique described by Chris yesterday and the results are shown below.

Back to the question ... the question had to do with High Pass - where does the name come from? Many folks use High Pass. Others are confused by the name and leave it alone. Some worry that it might not work as a sharpener as it's not found in the Sharpen sub menu, it's found in Filter>Other. So what's with the name?

High Pass removes low-frequency detail whilst preserving edge detail in areas that contain sharp colour transitions. In other words, it lets the high frequencies pass through and stops the low frequencies. Yes, it's really that simple.

As far as the arson image goes, you can notice the richness of the colours and the enhanced contrast. All of this comes from within the single image using Chris' technique.

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