OK it’s time to get my head around sharpening once & for all! It’s something I naturally use at the end of editing every photo but I’ve never really understood what the three elements of “Unsharp Mask” did.
Radius. This controls how many pixels adjacent to the edges are sharpened (sharpening works by the software increasing the contrast along the edges of objects within the image). A small radius enhances smaller scale details eg. stray hairs, eyelashes etc. Usually a setting of 0.6 to 2.5 is used. Setting too high a radius can create unwanted halos around objects.
Factor. This affects the strength of the sharpening (how much darker & how much lighter the edges become).
Threshold. This controls how far apart adjacent tonal values have to be before they are considered an edge ie. before any action is taken. Low values should sharpen more because fewer areas are excluded. Therefore, for human faces for example, higher values should be selected whereas, inanimate objects such as still life images can take a lower value.
When using Affinity Photo always apply sharpening non destructively via the Live Unsharp Mask filter, Layer>New Live Filter Layer>Unsharp Mask Filter. By doing this not only can you switch this layer on & off to see what affect the sharpening has on your image but you can also come back to tweek your settings at a later date.
Using a small radius (eg. 0.5) & a large factor (eg. 3.5) will accentuate more of the finer details eg. the brickwork on a building. Using a large radius (4.0) & a smaller factor (1.0) accentuates the larger details & acts in a similar way to a clarity filter. For portraits or images of low contrast eg. skin, increase the Threshold slider gradually to prevent artefacts from being enhanced in these areas.
To sharpen an image in Photoshop Elements I usually turn to “Unsharp Mask” (I had previously used “Adjust Sharpness”). However, I recently discovered an alternative method using the High Pass Filter. Now I have to confess I’m not sure if one is better than the other or whether they are merely three different ways of obtaining the same result. Having said that, from what I can gather the “High Pass” option appears to be primarily used on examples of highly textured images such as, animal fur.
The whole sharpening process works by the software increasing the contrast along the edges of objects within an image. Of course, Elements can’t recognise individual objects so it looks for areas where there is a sudden change in brightness or colour between neighbouring pixels. Our brains interpret this increased contrast as being “sharper”.
There are several methods on the internet of how to use the high pass filter. Some convert the image to a “smart object” first, others head straight for the filter menu. The one described below uses the latter. (As usual, sharpening should occur after you’ve completed all your other processes).
Duplicate the layer “Ctrl+J”. At this stage opinions seem to differ. One method desaturates the image “Shift +Ctrl +U” first. Filter>Other>High Pass. Set the “Radius” to somewhere between 0.5 – 5.0 pixels. Not too much or you will end up with additional noise in the image (if you see any white on the grey screen you’ve gone too far & will get halos). Click “OK”. Change the blend mode to “Overlay” although “Soft Light” (slightly less) & “Hard Light” (slightly harsher) are also viable options. The second method doesn’t bother to desaturate the image & sets the blend mode at the start. This way you can view how the image changes as you increase the radius size.
Once complete, if you feel the effect is too strong, lower the opacity. Alternatively, you can duplicate this layer to increase the effect. If you find the image looks good in some areas but not others use layer masks to apply the sharpening more selectively.