What is High Pass Sharpening?
Every digital image you capture records the scene in front of you depending on the settings in your camera. The sensor measures the light hitting the cells and the camera processor turns this into an image. Depending on how you shoot, it might be heavily processed into a JPEG file (if you shoot in JPEG format) or it may be lightly processed into a RAW file. Either way – the important fact to remember is that it is processed in some form.
Once you review the image at your leisure, you may decide that it’s not sharp enough and want to do something about it. Some reasons for lack of sharpness are:
- Missing the focus point: Maybe you hit the portrait subject’s ear instead of their eye and the eyes are a bit blurred.
- Poor lens quality: Some lenses are not as good as others and things like edges of photographs can sometimes be a bit blurred, especially on wide angled lenses.
- Lens out of alignment: Maybe your lens is faulty?
- Not sharp enough: Maybe the processing in-camera (either RAW or JPEG) didn’t sharpen the image enough for you.
- Movement: You moved during the shot and blurred it.
- Aperture: Some lenses are considered to be “soft” at their widest apertures. (f1.4 for a 50mm f1.4 for example, or f2.8 on a 70-200 f2.8 lens)
Software can take care of sharpening for you. Lightroom has excellent sharpening tools for example, as does Adobe Camera RAW. However the High Pass sharpening method (in Photoshop) allows you to have a degree of control not only of how much sharpening you apply, but where it is applied too.
So you can see for yourself, here is a landscape image that was a hand-held HDR, so there is a blur to the branches of the tree (you may need to do a page refresh to see the image whilst I iron out some creases). Drag the slider (or just click on the image) to see how sharpening has improved definition in the tree branches but hasn’t affected the sky or foreground.
High Pass Sharpening In Photoshop (CS5): The Process
The process is very simple and has a lot of flexibility.
- Open your image in Photoshop
- Duplicate it with CTRL+J
- Click on Filter>Other>High Pass. This should make everything go grey. Don’t panic. The pop up box should be asking you for the pixel radius. Now, the radius you set and the effect it has will depend on your overall image size. You want to adjust the slider so that the edges are peeking through the grey. For my 50D which has an example 5000 x 3000 pixel image, I tend to use a radius of between 3 & 5 pixels. On lower resolution images though this will have a more pronounced effect.
- Change the Blending Mode from “Normal” to either Soft, Hard, Vivid or Linear light. “Soft” will give a much more delicate effect. Linear light gives a very pronounced effect. I find “Hard Light” to be the best “middle ground”.
- (Optional) Reduce the Opacity if you need to. This allows you that last degree of control over the whole sharpening process.
That’s it. Dead simple.
The last step is another optional one. In y example image above, I have just applied sharpening to the trees. How is this done?
Optional Step: Layer Masking
Layer Masking is quite a simple technique and really useful for other areas of Photoshop and not just sharpening. It does require a bit more work though.
If you look down at the right hand lower corner, you should see your background, with “Layer 1” above it (your sharpening layer). Photoshop builds images in layers so you have to imagine that you are looking down at your image (the background layer) through the sharpening layer. What Layer Masking does is “erase” bits of the sharpening layer to allow some parts of your image to be sharp, and others to retain their blur.
- On the bottom row, next to the “fx” button, you should see a rectangle with a little hole in it. Hovering over it should give you an “Add Layer Mask” pop up. Make sure your “Layer 1” grey sharpening layer is selected, then click on the rectangle. You should end up with a white box next to your grey layer.
- Press “D”, then “X”. This should set your foreground colour to Black and your background colour to white.
- Pick a soft edged brush and set the opacity to 50-80%.
- Start Painting on your image. Now, wherever you paint black on the mask will “block out” your sharpening. “X” will swap your foreground to white which will “reveal” your sharpening.
If you start getting black paint on your image you’ve probably selected the background by mistake.
This technique allows you to “paint out” sections of the image you don’t want sharp with a very fine degree of detail. So what about when you want to reverse the process? Let’s say you have a portrait where you want the eyes to be really sharp, but not the rest of the face, it’s a very long job to sharpen the image, then spend hours painting everything around the eyes.
In step 1, before you click the “Add Layer Mask” button, hold down the Alt key (Alt+Click). This will create a mask that’s automatically black and you can paint white straight onto the image. This will save a lot of time if you’ve only got eyes to sharpen (for example).
Hope you enjoyed this short tutorial. High Pass Sharpening is a great and simple to use technique.