Bandpass Filtering

The bandpass filter is an effect that expands upon the basis of all image sharpening techniques. Sharpening processes compare the high and low frequency of two image layers allowing for or taking away the appearance of sharpness. To create a bandpass filter we will follow the the formula above.

Begin by duplicating your image so that you have 3 identical files. Using a Gaussian blur filter give the first file a "lesser blur" with a radius of 4 pixels. Do the same for the second file but give it a "greater blur" with a radius of 6 pixels. Making sure that you have the second file selected, go to Apply Image. Your source will be the lesser blur file, and the target will be the greater blur file. Change the blend mode to subtract and click OK. Your greater blur file will appear black at first, but by creating a levels adjustment layer we can push the image until we clearly see the edge detection. Repeat the process to your third original file, this time using your newly changed greater blur file as the source, and changing the blend mode to add.

Your final product should look something like the image above, but all images vary and will need individual tweaking to get the best results.