Tuesday, August 12, 2008

Unsharp Mask settings

OK look. Sharpening, and Unsharp Mask in particular, seems to spark intensely complex and heated debates. My strategies are really simple, and I think plenty effective, and are very much specific to digital photography, not necessarily for scanned images. Here are my settings, a bit about why, and that’s pretty much all I have to say about it. As my friend Paul says, let’s pay our respects and move on.

First, it’s absolutely crucial that you have sized your image to it’s final size and resolution. You must apply Unsharp Mask as a very last step in your process, just before you print. (On that point I think we all agree.)

Here I’m going for a print for an 8 ½ x 11” sheet of paper.

Next, do yourself a favor and turn your Rulers on. (View>Rulers, make sure it’s checked, or simply Command R.)

Now, and this is a point of contention, view the image at “Print Size”, NOT “100%”. (Zoom Tool, the button for Print Size is in the toolbar, to the right.)

This lets you look at the image at roughly the size it will be printed by your printer. Viewing at this size insures you will not over, or under-sharpen for the print size you’re making. (That said, mostly I zoom in one or two clicks from the “Print Size” setting to actually get the thing to display at the right size. That’s why I like the Rulers visible, so I can match up one inch on the display with an actual inch. “Print Size” uses your screen resolution to take a stab at the right size, and if your screen is a high res display you’re going to get an image that shows up as too small.)

Now you can hit Filter>Sharpen>Unsharp Mask.

Preview is selected. Do not look at the Preview screen in the Unsharp Mask window, look at the main image that Photoshop is showing. Now you can make your adjustments intelligently.

Step one is to lock the Radius setting to .5 pixels. This departs from the standard 1 pixel setting Photoshop defaults to, and means you have to compensate by increasing the amount. That is why my Amount seems high, at anywhere from 150 to 350%. The Threshold setting feathers the effect back, by adding more “levels” to the increase in local contrast (the contrast between pixel neighbors, which is what makes the image appear sharper). I run this between 2 and 7.

These settings correspond to the size of the image. A bigger image needs more “Amount”. A smaller image, smaller Amount. The Radius is always, always at .5 pixels. The rationale behind this is simply that this produces a nicer sharpening effect with digital capture files than other settings I’ve tried. It gives you a subtle, crisp edge, and avoids the dreaded halo of a nasty sharpening job.

Here’s a particularly hideous example of that halo effect. Note the black line, and the areas that are lighter bordering that line. They taper off to the normal tone, a fair distance away from that line.

This is what we’d prefer it look like. Nice even tones leading up to some hard edges.

In case that’s not enough to spark a nice heated exchange on a digital photo forum, I have one more thing to add. I very rarely apply sharpening over the entire image anymore. It really seems that there are very few instances where you want to sharpen everything. In the first place, Unsharp Mask needs an edge, and if there is no edge it won’t have anything to work with. Areas that are out of focus, or areas of tone or color without an edge may get some unpleasant effects, most often an undesired enhanced noise or “grain”. In the second place, it’s just something that, well, isn’t what I want in every area of the image. In a portrait, for example, I’ll only sharpen the eyes and the hair to give the image some snap. I will almost never sharpen the skin or background.

Of course, I use my masks to control this, but you saw that coming, right?

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