Anything Photoshop or Photography

Unsharp Mask Filter In LAB Mode


I have been experimenting with all types of sharpening methods over the last few months. I really liked the High Pass Sharpening method that is very popular, the new improved Sharpen Tool in Photoshop CS5, and the Smart Sharpen Filter that so many use. Recently I read Harold Davis‘ book The Photoshop Darkroom where he gives steps to sharping in the LAB Mode. I have now started using this method – it takes a little more time to do, but I believe it really gives the best results. Since I take a lot of time with my images, like to print them, and don’t batch process, it is important that each image gets the best sharpening I can do.

The above image of the fruit shop along the road on the Big Island in Hawaii is an good example of how nice the sharpening can be in an image. Both Nik Color Efex Pro 4 and Topaz Simplify 3 (see sidebar at my Tidbits Blog for website link) were used in Photoshop to get the rich colors. The LAB sharpening was done after most of the adjustments were made to the image in Lightroom and Photoshop.

Why use LAB Mode sharpening? The most important reason people use it is to keep the colors true and not be influenced by any color shifting that other RGB Mode sharpening may produce. By using a black layer mask, the image is first over-sharpen and then just areas that need the sharpening can be painted back into the image selectively and to various degrees so it does not  have that over-sharpened look. This process also works really well on portraits where just the eyes are sharpened or on areas you want to draw attention to a certain part of an image.

The workflow steps to get this effect are easy:

1.  Apply most of the filters and do  clean up to your image before the next step. Just be sure there are no adjustment layers in the document or they will be discarded upon the conversion. You will need to save the image as an unsharpened version and then flatten it to proceed.

2.  Go to Image -> Mode -> LAB – Click “Don’t Rasterize” and “Don’t Merge” buttons.

3.  Duplicate the layer by clicking CTRL+J.

4.  Go to the Channels panel and highlight the L channel.

5.  Turn on the top eyeball so all channels are showing but only the L channel is highlighted.

6.  Go to Layers Panel and to Filters -> Sharpen -> Unsharp Mask.  I like Harold Davis’s recommendation to start with these settings and adjust from this point.

Radius  2.7   – The higher the Radius setting, the more sharpening occurs
Threshold 9   – The lower the Threshold setting, the sharper the image
Amount  – somewhere between 50-120

Watch out for noise enhancement, especially when adjusting the Amount slider.

7.  Add a black layer mask to layer by holding down the ALT key and clicking the Layer Mask icon at bottom of Layers Panel. Using a soft white brush set to 30% opacity, paint back in the areas you want sharpened leaving areas with noise or over-sharpened edges unpainted. Paint over several times to enhance the effect.

8.  Go to Image -> Mode -> RGB and press the “Don’t Flatten” button. Now you can add your Curves Adjustment Layer and frames to finish up.

Dan Margulis (one of the first three people ever inducted into the Photoshop Hall of Fame) is the most knowledgeable person when it comes to using the LAB Mode and has written the best book ever on the subject, Photoshop LAB Color. He covers LAB sharpening very thoroughly.


Here is another example of how great this type of sharpening works – it is great to be able to localize where the actual detail is emphasized. This old vintage car was parked in front of the Casa Monica Hotel in St. Augustine, Florida. It is a three image HDR photo processed using Katrin Eismann’s workflow – see my blog HDR Using Photoshop Merge to HDR and Nik”s HDR Efex Pro and Silver Efex Pro? Wow! (used Granny’s Attic preset in HDR Efex Pro and Structure Harsh in Silver Efex Pro). Nik’s Viveza 2 was used to increase the detail and color in the wheels and curtains in the windows. Then it was taken into the LAB mode and processed using the Unsharp Mask Filter (settings Amount 98/Radius 9.4/Threshold 1). Using a brush set to white at 30% opacity, the wheels, curtains and lettering were painted back in. I wanted the rest of the image to have that grungy old feel to it which HDR Efex Pro gave the image. OnOne PhotoFrame (see sidebar at my Tidbits Blog for website link) Kevin Kubota Flower was added as a last step.


The LAB Unsharp Mask was used on this image of an elephant puppet from Burma that was on display at the Hilton Waikoloa Village on the Big Island in Hawaii. To see how it was processed see my blog Nik Color Efex Pro 4 Just Does It Right! The sharpening was applied as the last step and it was selectively painted in to just the details in the elephant but not the background. This really made the details in the puppet stand out.  Also all the images but the Lightroom image in my blogs Can a Pseudo HDR Image be as Good as the Real Thing? (Part One) and Can a Pseudo HDR Image be as Good as the Real Thing? (Part Two) used this method on the bicycles very successfully.

I am not really sure why, but I definitely see an improvement in sharpness using the LAB method of sharpening. There are times when not that much needs to be sharpened in an image and the Sharpen Tool is enough or Nik’s Viveza 2 adds enough sharpening so this process is not necessary. I do think it works really great on my landscape and HDR images where I want a very clear edge on most of the objects. Give this easy method a try and see what you think…..Digital Lady Syd

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