Photoshop Technique: LAB Sharpening

LAB Sharpening

Sharpening is something that almost any image can benefit from. Like saturation, it can easily be ignored or overdone if you’re not careful. When done right, it’s a subtle change that results in a big improvement.

!!! For the sake of presentation and comparison, the images shown in this post are highly exaggerated examples of sharpening. These images are NOT good examples of proper sharpening. At the very end of the article, I’ve shown the true sharpened photo in comparison with the original !!!

It seems that there are many ways to sharpen a photo, and the most common is Photoshop’s Unsharp Mask. It’s a fine tool for most cases, but it can produce terrible results when used incorrectly or without caution. I, myself, usually fall back on the Unsharp mask for a majority of my sharpening needs. But using this tool in the RGB color space is not ideal!

Recently I posted an article about a LAB Saturation Photoshop Technique — and this article is much the same, but with a focus on Sharpening. LAB (Lightness, A, B) color mode is a great way to increase the quality of a tool such as the Unsharp Mask or other sharpening methods. So open up a photo that could use some sharpening and follow allong!

DOWNLOAD THE PHOTOSHOP ACTION

Just like with the saturation article, I’ve put together a Photoshop Action that will assist you in speeding up the process of LAB Sharpening. I’ve been using this action for the last several months and I can honestly say that I’ve been using it with every photo that requires sharpening. As with the saturation action, you simply select the top layer, run the action, choose your Unsharp Mask settings, and when presented with a location to duplicate to, just choose your original file. And before running the action, read through the steps below to get a better idea of what it’s doing.

1. OPEN YOUR IMAGE AND DO YOUR STUFF

RGB Adjusted

The RGB color mode is the most common to work with, so I’ll assume that most of us use this as our default. We can still work in RGB even though we’re doing adjustments in LAB color mode — it’s just a little extra work. So open up your image as you normally would and basically process the entire image until you’re happy with it.

Sharpening should occur as the very last step in your workflow for two main reasons: 1) It’s a very localized adjustment of brightness and any further processing will exaggerate it beyond your original intent, and 2) It’s a destructive process, so we’ll be using a copy layer for the sharpening — and if you stack adjustments on top of those layers, it makes life very difficult if you choose to go back and rework the sharpening.

2. OPEN A COPY IN LAB MODE

Make a copy of the visible image by doing a “Stamp Visible” command (Ctrl+Alt+Shift+E). This gives us a single layer that contains all of the underlying adjustments we’ve applied. Now take this layer and duplicate it to a new document. Once in that new document, change the color mode to “LAB”. Why not just change the color mode in the original file? You’ll lose any RGB-specific adjustment layers such as the curves adjustment we just applied (go ahead, try it and see what happens). OK, so now we’re working with LAB and we’re ready to sharpen that photo.

3. SHARPEN THE LIGHTNESS CHANNEL

The lightness channel contains all of the light and dark tones in the image while avoiding any noise caused by the color channels. Sharpening works by darkening the darks and lightening the lights at their boundaries. Any color noise will cause noisy sharpening, so we’ll just avoid it altogether. In this example, I’ll use the Unsharp Mask to sharpen the image. In truth, you could use whatever method you prefer in place of that — the key is to do it on the lightness channel.

LAB Adjusted

So switch to the channels palette and select “Lightness”. The “A” and “B” channels should be deselected and your image should look like a black and white photo. Now, apply your sharpening directly to that channel. For the Unsharp Mask, you can find it under Filter >> Sharpen >> Unsharp Mask. I typically start with an amount of 100%, a radius of 1.5%, and a threshold of 1 — but every image requires different settings, so don’t just assume that those numbers are the best. Once you get the sharpness where you like it, apply the filter and reselect the “LAB” channel in your palette.

4. COPY BACK TO THE RGB IMAGE

Now go back to your layers palette and copy that layer back to your original image — it should convert itself back into RGB when you copy it over.

Once you’re back in the original image, you’re pretty much done with the adjustment. You can now toy around with masking and opacity settings to get the final look you’re after. Sometimes I’ll over-sharpen the sharpest areas just a bit then go back and partially mask out those areas that didn’t need much sharpening. This allows me to properly sharpen the majority of the image.

A COMPARISON OF THE RESULTS

Now for the fun part — let’s evaluate just how much better this technique is from an RGB image that’s been sharpened with the Unsharp Mask. Sometimes the old RGB method will work out better for you, but in my opinion, the LAB sharpening is much more natural with fewer halos and color oddities.

You folks reading this on the feed will have to pop over to the site in order to see these mouse-over effects.

LAB Sharpened (shown), RGB Sharpened (mouse-over)
Each of these were sharpened at 200%, 3 pixels, and a threshold of 0.
See the white halos, discoloration, and over-saturation on the RGB version? This is why LAB is the way to go.
Labsharp 500

LAB Sharpened (shown), Unsharpened (mouse-over)
Labsharp 500

RGB Sharpened (shown), Unsharpened (mouse-over)
Rgbsharp 500

True LAB Sharpened (shown), Unsharpened (mouse-over)
This one was done at 65%, 1 pixel, and a threshold of 1.
Truesharp 500