Learning Paths

Photoshop – sharpening in LAB mode

While Photoshop’s sharpening filters are very good, the way they work can seriously damage the original image. But, this damage can be avoided – entirely.

How does Photoshop sharpen images?

Sharpening an image implies adding detail, but Photoshop can’t do this. Instead it enhances the contrast along all the visible edges. The ‘spread’ of this effect is a radius based on a number of pixels, and the ‘amount’ is how strong you want the enhancement to be. These settings can be found  in ‘smart sharpen’ and ‘unsharp mask’ (both under ‘filter > sharpen’). In addition, Unsharp Mask has a ‘threshold’ setting which determines the range of colours in the image which will be affected. A setting of zero applies the filter to the entire image.

original image, image
The original image with no sharpening applied

Using Unsharp Mask:

Choose ‘fliter > sharpen > unsharp mask’. Usually, use a ‘threshold’ of ‘0’, a ‘radius’ of between 1 and 2, and an ‘amount’ of whatever you think the image needs. Bear in mind that if you can see weird halo edges appearing, it will look much stronger in print. The key advice here is: back off the settings a bit.

If the image is too blurred for this to work, you may be tempted to overdo it. OK, we’ll overdo it: here’s the result using a radius of 20 and an amount of 250 – way over the top!

unsharp mask, image
Unsharp Mask sharpening – seriously overdone

Using LAB mode:

1) Change the colour mode of the image to ‘LAB’ (‘image > mode > LAB colour’)
In LAB mode, you can go way beyond what you’d normally think possible, without damaging the colour at all. This is because LAB stands for lightness, A and B. The A and B channels hold ALL the colour in the image, while the lightness channel only holds the light and dark information.

2) Open the Channels window

Don’t mess around with the A and B channels, or you’ll park your image up a tree faster than you can believe possible. Instead, click on the ‘lightness’ channel and apply the sharpening to it – at the same level used in Unsharp Mask. It will look awful. Don’t worry.

3) Reselect the ‘LAB’ composite channel at the top of the Channels window to see the result.

In LAB mode you can sharpen an image way beyond what is otherwise possible – without distorting the colour.

It may be a very stylised image, but as the lightness channel doesn’t contain any of the colour, none of the colour gets distorted. So it’s still an image that you might be able to use – which is a whole lot better than not being able to use it at all!

Give it a try! And let us know if it’s helpful… Leave your comments below. And please feel free to share this article using the buttons below.