Lightroom 3 - Sharpening & the "Alt" Key

Click for larger image

Last winter we discussed the Lightroom 3 Detail Panel in the post "The Lightroom Detail Pane".  In that post we learned how to use the "Alt" key to help mask your image before applying sharpening to the photo.  What we didn't discuss, however, is how the "Alt" key can be used in combination with ANY of the Sharpening sliders to help identify what areas of your image will be impacted by the adjustment and to what degree.

To help illustrate, we've invited young Mr. Grosbeak here to assist.

The Sharpening Exercise

How much? How little? What for?...  Guess what.  Just with all other adjustments in Lightroom, there is no "stock answer" except for "It depends.".  It depends on your intended output (screen, print, etc), your personal preferences, the photo itself.  The best I can do is share with you my version of "how to" and the rest is left to you and your experimentation.

Step 1 - Masking

In most Lightroom adjustment panels, I find the "top down" approach often works best.  That is to say you would adjust the sliders in the order they are presented starting at the top and working your way down.  Except for the Sharpening panel. :-)

If you expand the photo above, you'll notice there is a fair amount of noise in the blue sky background.  I'd been trying to capture one of those zooming hummingbirds feeding in the crab apple blossoms so I had my shutter speed cranked up to 1/1000th of a second (still isn't fast enough btw) which resulted in an ISO of 1100 in this case.  The thing I DON'T want to do while sharpening this image is to further enhance the noise in that blue background.  Enter the Masking slider.

 

By holding down the "Alt" key while sliding the Masking slider, a negative of your image will appear.  You'll notice the image to the left (Masking = 30) still shows a fair amount of grain in the dark area.  Continuing to drag the slider until that grain goes away (see right image, Masking = 57) will ensure that whatever additional sharpening adjustment you makes will only apply to the non-black (masked) areas.

Step 2 - Detail

The Detail slider is responsible for the edges in your image.  As a general rule, I don't find I adjust this slider much UNLESS the other sharpening adjustments have introduced the dreaded "halos" around your edges.  In that case, moving the detail slider to the left can help mitigate the halos.

In our sample image above, the edges of the soft flower pedals are probably not going to be as noticeable as say the head feathers on the grosbeak.  When working on more detailed areas like this, I prefer to leverage the preview panel inside the Detail adjustment pane at a 2:1 magnification (right click on the preview to change magnification).

Holding the "Alt" key down while moving the Detail slider provides a sort of "embossed" look that will give you a better view of the detailed edge.  When making these adjustments I usually move the slider all the way to the left and then gradually bring it back to the right until start to notice more pixelation of the area you're adjusting - in this case the head feathers - and then back it down just a hair.

CAVEAT: When making adjustments in the preview window, the preview doesn't seem to be respecting the masking you've already applied.  In other words, the sky portion of the image also appeared to be impacted by the adjustment, but this is limited only to the preview and not the actual image.

Step 3 - Radius

The Radius slider controls how far out from the edge will be impacted by the sharpening adjustment.  Using the "Alt" key in conjunction with the slider will again present that "embossed" view to allow you to better see the impact on the edge. 

In this screen shot, I've moved the slider all the way to the right to illustrate how the edge is expanded by a white halo in the preview screen.   You may want to also be sure that you have the main window zoomed in at 100% and keep an eye on the "white halo" on the other parts of your image.  Back the slider down until white halo just disappears.

Step 4 - Amount

Up to this point we've only adjusted the supporting settings for the actual sharpening.  As the Lightroom default for the "Amount" setting is 25 and not 0, those adjustments have already made noticeable changes in your image.

Holding down the "Alt" key in combination with the "Amount" slider reveals a grey-scale image.  There is really only one scenario in which I find this to be helpful and this image is a good example.  If you have a high degree of color saturation in your photo it can sometimes be difficult to recognize the effect of the sharpening adjustments in those areas.  The red-breast on the grosbeak is a good example.

When adjusting the "Amount", it is again a good idea to zoom in to 100% on your main image as well as focus on a particular important area of  your image inside the preview window at 2:1 magnification.  Slide to the right until the edges start to go "too far" and then back it off just a little bit.

Once you're satisfied with the amount of sharpening applied, you may find it necessary to go back and fine-tune some of the other settings.

One last sharpening tip.  If there is anything in your image with an eye that isn't a potato, make sure to give it special attention in the adjustment process.  Again, using the preview window at 2:1 magnification helps that process.

Until next time, keep click'n.

-Ken