Multi-Level Sharpening an Image

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I can’t even start to count the number of books, articles and tips that are written about sharpening. There are so many recipes and so many methods that it gets confusing. In this small article I will describe a simple technique to control the amount of sharpening in an image. It’s a technique commonly used in astrophotography where the finest level of sharpening is needed and it can be applied to daytime images without any difference.

Using the HighPass Filter for sharpening

The tool we’ll use for sharpening is the high pass filter. The method is simple, duplicate the layer, apply the highpass filter to the new layer and set its layer mode to overlay. You will see how the new layer is a sharpened version of the previous one. To control the level of sharpening you change the radius of the highpass filter. A very small radius is useful to enhance textures without modifying the rest of the image. A larger radius can increase contrast in the edges. A very large radius will increase local contrast a lot but will probably create some artifacts.

The filter in action

To show you the effect of the filter I will show some images with different levels of sharpening applied.

Original Image

Original Image

HighPass Filter Radius = 1 pixel

HighPass Filter Radius = 1 pixel

High Pass Filter Radius = 10 pixels

High Pass Filter Radius = 10 pixels

High Pass Filter Radius = 20 pixels

High Pass Filter Radius = 20 pixels

You can see how increasing the radius changes the amount of sharpening applied to the image.

Sharpening Textures

If you want to enhance local contrast in your photo textures you should apply the filter with a radius of less than 1 pixel. 0.3, 0.5 and 0.7 are good values to try. This values will enhance micro-contrast in your textured areas without impact in the rest of the photo.

This is a example:

Original

Original

High Pass Filter Radius = 0.5 pixels

High Pass Filter Radius = 0.5 pixels


 
If you look carefully you will see how the texture is enhanced.

Different Levels of Sharpening

As we have seen we need different levels of sharpning for different things. The best approach is to create several copies of your original photo and apply the highpass filter to each layer with a different radius. Then you can use masks and opacity to decide the amount of sharpening to use from each layer and where to apply the changes. I use a very low radius to highlight textures, a 2 or 3 pixel radius for general areas of the image, a 5 pixel value for edges and a 10 or 20 pixel value for things such as grass or clouds where a higher level of sharpening can be needed.

This is how the layers look while editing:

 

Once we have all the different levels of sharpening masks and opacities are used to decide how the final image will look.

Original

Original

Finished

Finished

Final Sharpening Tips

Sharpening should be applied only to the final image once resized. Save your master photos in full size without applying sharpening at all. Then when you want to print it or put it on the web resize the image, apply sharpening a save a jpg to be used for printing or publishing. Different sizes need different levels of sharpening.

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  1. thinsmek

    This is a very good post! Thank you for simply explaining how sharpening can be used for different purposes.

    • Reply
  2. codrin dinu vasiliu

    because i want to control the level of the sharpening in real time with preview, i do a small modification in this technique. first i do the overlay on the new layer. then i apply the high pass filter on this layer and in the dialog box i use the preview mode.

    • Reply
  3. George Bailey

    Thanks for the post, Luis!
    This is also my most used shrpening process, but with one slight difference – I use Soft Light instead of Overlay mode for layer blending, I believe it makes the effect more gentle.

    • Reply
  4. Vic Cano

    High Pass is a great filter but with some textured image, I usually use unsharp mask esp for old people and hair.

    Try these values or better yet, duplicate the orig file then apply these settings:

    Background copy
    USM 18-40-0
    USM 150-.3-0
    Edit>Fade USM 100% in Darken Mode
    USM 150-.3-0
    Edit>Fade USM 50% in Lighten Mode
    Flatten image

    once you got the two image, you can go ahead and use masking as to where you want the sharpening to be more visible. Hope this one helps as well.

    I learned this from one of our local trainings regarding sharpening image using unsharp Mask (USM)

    • Reply
  5. Stefano Ciurli

    How do I do that with Aperture or Color Efex? Is there a way not to use layers?

    • Reply

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