High Pass Filtration

I usually don’t post information about Photoshop techniques simply because there is an entire universe of websites dedicated to Photoshop that are run by folks who are far more Photoshop savvy than I could ever hope to be. However, every so often I run across a technique that I find really interesting and so, on those occasions, a post about it seems reasonable. Such is the case with High Pass Filtration. Please don’t consider this to be the definitive ‘how to’ regarding this technique but, rather, a jumping off point to look into it in a more sophisticated manner if it seems of interest to you.

The reason I found High Pass filtration interesting is that while ‘surfing the net’ I have occasionally come across images that seem to have a somewhat ‘enhanced’ sense of reality that gives them a very three dimensional appearance. The effect seems somewhat similar to the HDR effect, but tuned down. When I have followed discussions about such images the photographer will often say, when asked, that the image in question was not processed with HDR software.

So, it whet my interest when I ran across a technique which, by description, seemed to be one way to generate this effect. It is done by using the Photoshop High Pass filter to increase contrast. I knew that this filter could be used for sharpening and, of course, contrast enhancement is a form of sharpening.

At any rate, here is a way to use this technique in order to see if it will achieve a desirable effect (plus I made my own little addition to what I read). Once the image you are considering using it on is complete, duplicate the image and flatten it, but don’t sharpen it yet. Now the image consists of only a background layer. Duplicate this background layer twice and click the icons to turn these duplicate layers off, making them invisible. Now click back on the background layer to make it active and go to the Photoshop filters and choose High Pass (Filter>Other>High Pass). You get a dialogue box in which you can choose a radius. Choose 75 pixels to start, but this is obviously a ‘jump off’ point for experimentation. Your image will now look totally disgusting. Don’t worry….just click on the duplicate background layer which is directly above the layer that was just filtered to make it active and then click on the icon to make it visible. The image now returns to the way it looked before starting this whole thing because it is a duplicate of the original at 100% opacity lying on top of the filtered image. Now the fun begins. Change the blending mode of this layer from normal to overlay and the image undergoes an interesting change.

Perhaps the effect is too much? That is why I added the second duplicate layer (which is not visible at this point) on top of the others at the start of the technique. Click on that layer to now make it active and click on the icon to make it visible. The image now appears as it did before starting. But turn down the opacity of this topmost layer to let the filtered look come through and see how you like it.

A few comments:

1) I have only played around with this technique a bit and found that there are some images that it truly enhances and others that it totally destroys.

2) If an image is found that would benefit from this technique, the entire process can obviously be performed within the original file by duplicating the entire image and placing the entire image on a new layer and working from there.

4) It really is difficult to duplicate this effect with curves....I tried.

3) With the image size being so small, and with the effect being toned down with the topmost layer blogs don't really lend themselves to really demonstrating the effect well…..so, if it sounds interesting, play around with it on your own images and see what you think. With that in mind I am posting one example. The only difference between these two images was the High Pass filtration step.

Pre High Pass Filtration
Copyright Howard Grill

Post High Pass Filtration
Copyright Howard Grill