The Unsharp mask filter in Photoshop is very important for the photographer. It provides an easy way to reinforce the precision (and the apparent focus) of a photo picture. Quite naturally, you will be deciding to use the lightest accentuation on your camera (most SLR cameras give you a lot of freee choice here), and leave the accentuation work for Photoshop editing.
Generally speaking, the Unsharp mask of Photoshop is very powerful, but it tends to be “too powerful” and sometimes leaves a kind of unpleasant halo. For example, check the effect of this filter (applied at the maximum parameters) on the black and white wings of this yellow-billed stork. The grey areas are bordered with white near black zones and with black near white zones.
As if halos were not enough, there is also a kind of color shifting around very little zones of color. Check the head of the stork and you will notice that very small colored spots are transformed into major color patches that look like a complete recoloration.
Consequently, you are often advised to limit yourself when applying the Unsharp mask:
Don’t use too large values for
Amount and too small values for
This is reasonable, but there is also an intermediate approach which gives you more flexibility in the application of the Unsharp mask, without most of its drawbacks on the final image.
You must go through these steps:
- convert your image from RGB color space to LAB, using Image>Mode… menu,
- select the
Lightlayer in the
Channelspalette (or with
- apply the
Unsharp Maskto this layer,
- convert back to RGB.
This reduces a lot the impact of halos and avoids most of the color shift that normally goes with the strongest parameters.
Try it by yourself, and you will find it quite appropriate.
Note: One of the nice things I find in this method is that you can apply nearly mechanically the conversion steps, your attention being concentrated onto choosing the right unsharp parameters.