A Couple of Basics – Gaussian Blur and High Pass Sharpening

Article by Jim Denham

With the sophistication of editing software these days, it’s easy to get caught up in the latest techniques and plug-ins. One of my Christmas gifts was onOne’s Perfect Photo Suite 7 upgrade and for my birthday, the Nik Software bundle from Google. These are some amazing and powerful tools that help keep photo editing fun and efficient and I really enjoy them. Sometimes, however, it’s good to go back to some of the basics I learned early on in my photographic journey and see just how impactful they can still be in producing strong images.

Two of the first techniques I learned in editing images were the Gaussian Blur and High Pass Sharpening. These are not complicated filters and can usually be found on any basic piece of editing software, like GIMP or Photoshop Elements. Let’s grab a photo and see how to apply these filters and changes that can be achieved with them.

So, we’ve got a tone mapped image (below). It’s a great fall scene just outside the parking lot at work – most people at work have a hard time believing that, but it’s true. You have to be on the lookout for shots like these, even in the most unobvious places! It was blended using 7 exposures, from -5 EV to +1 EV in Photomatix. Starting in Aperture (my workspace), the first step is to export the image to Photoshop Elements!

 

To be honest, this image looks pretty good right out of Photomatix, but I want to apply a bit more contrast, saturation and richness to it to make it more bold. Here’s how. First thing’s first, duplicate the layer in PSE so that we do not effect the original. Then it’s up to the ‘Filter’ menu, ‘Blur’ then ‘Gaussian Blur’.

A Gaussian Blur dialog box will pop up allowing you to select the amount of blur, in pixels, you’d like to apply to the image. A rule of thumb here is to apply enough blur that the ability to make out the elements of the image is only slightly possible. Usually this comes to between 20-25 pixels depending on what your image has in it. Once you have the settings you desire, click ‘OK’.

That’s it! Not so much, huh? Now all we have is a blurred image and it’s not much good to us, that is, until we hit it with a blending mode. Just above the Layers Panel is a pull down list of Blending Modes, ranging from Normal, which doesn’t apply any effect, to Luminosity, which can add a bit of contrast to the image. You can experiment with all of these modes and see what works for you, but in this application, I tend to stay in the range of Overlay to Hard Light. Let’s grab Overlay and see what it does.

 

 What the Overlay Blending Mode produces is a heavily saturated, heavy constrast image, which is too far over the top for what I’m looking for. From here there are two options, 1) adjust the Opacity slider to the right of the Blending Mode pull down to lesson the effect, or 2) select a slightly weaker mode like Soft Light that will yield a more toned down version. The image has all of the properties I want using the Overlay mode, it’s just a bit too far, so I’ll choose to move the opacity down to a more acceptable level. I like what I see at 50%. There’s a great deal of flexibility here, so suit yourself on what works best for your taste and image.

What we have now is an image that has strong contrast, glow, saturation and richness. It’s just a bit too soft, though. Here’s where the High Pass Sharpening comes in. On your Mac, press Shift – Option – Command – E (I believe that would be Shift – Alt – Control – E on a PC) to create a composite layer from the adjustments you’ve already made. Then click on the ‘Enhance’, ‘Adjust Color’ and ‘Adjust Hue/Saturation’. Once there, move the Saturation slider all the way to the left to remove all color from the image. I don’t know if this is absolutely necessary, but it helps me to see where the sharpening is taking place better than in color.

 

 

To apply the High Pass filter, go back up to the ‘Filter’ menu, go down to ‘Other’ and click on ‘High Pass’. You should see a dialog box similar to that of the Gaussian Blur with a window of the image and the high pass setting in pixels. Unlike the Gaussian Blur settings, I like to keep this one to a maximum of 5 pixels, otherwise it can show some slight halo effect where the sharpening is placed. You can see the adjustment both in the dialog box window and also in the actual PSE working area, which I use to see exactly where the sharpening is applied. There should be no detail in the areas with smooth edges, like the sky in this case, but you should be able to see that the trees are being affected.

This step may take some trial and error to get the amount of sharpening you’re looking for, but once you’ve got what you like, click ‘OK’. Once again, we need to go back to the Blending Modes to finish this off, otherwise you have a slightly sharpening grey skeleton of an picture, which looks kind of cool if you like stuff like that, but doesn’t make for much of an image in my book. In most cases, I will use either the Soft Light or Hard Light modes with the High Pass filter. The harder the light, the higher degree of sharpening, so play around and see what you like in your image. For this one, I’m going to go with Soft Light to keep a bit of the glow away from the edges!

 

 

Just like with the Gaussian Blur, we can adjust opacity if the effect is too much for our liking, or, for both effects, they can be masked in using layer masks to selectively apply them to parts of the image rather than the whole. For this image, I may have wanted to keep the sky a bit more edgy and could have masked out some or all of the blur effect, or only masked in the sharpening in selective parts of the trees. Once again, it’s to your taste.

From here, we import back to Aperture or Lightroom where finishing touches can be applied and the image exported accordingly. There you have it!

Now, could you get this same effect from one of the plug-in modules like Perfect Photo Suite or the NIK Collection? Likely. But it only takes a few clicks here to make a couple of quick high impact adjustments that are totally flexible in application. That’s not to say stop using the plug-ins – I’m sure not going to – but it’s always good to have a couple of basic tools at hand you can apply quickly and selectively to get an image where you want it!

Jim Denham

Jim loves all things photography, but the obsession with the medium started with HDR and it continues to be a main tool in his processing belt. Jim’s portfolio consists of images both from his hometown area of Minnesota’s Twin Cities, as well as images from many towns around the US.

website: http://www.jimdenhamphotography.com/

Smugmug Galleries: http://jimdenhamphoto.smugmug.com/