Sharpening

[T Paul]

There are several ways in Photoshop to sharpen an image. The most commonly used are Unsharp-Mask (USM) and High-Pass filter.

USM Filter Basics: Sharpening increases the contrast at the edges of an image, ie, makes the dark pixels darker and the light pixels lighter. USM has three controls to adjust:

Amount: The higher the amount the stronger the sharpening. A small radius will need a higher amount setting. Katrin Eismann in her book Photoshop Restoration and Retouching suggests 120%-200% for offset printing and 40%-80% for direct digital output devices. For web or screen output, just eyeball it. As you increase the Amount parameter by moving the slider to the right, dark areas get darker and light areas get lighter. Do too much and you will end up sacrificing good pixels resulting in white halos and areas of solid black without any detail.

Radius: Radius determines how many pixels out from the color edge will have their contrast increased controls how much blurring is used in the edge-finding stage. Katrin Eismann suggests an accepted rule of thumb for offset printing is to divide the printer’s output resolution by 200 and use that as your starting point. As one web site puts it: "Radius is sort of like a brush size for the filter. A low setting limits sharpening to exact edges. A higher setting spreads the sharpening effect out according to the chosen radius."
This is the critical setting

Threshold: Adjusts how different the colors on the two sides of an edge have to be before the filter will recognize it as an edge and sharpen it. For example, a threshold Value of 5 means all tones within five value levels of 5 will be ignored.

[T Paul]

There are many suggested settings for all three sliders and they will vary from photo to photo. Your best bet is to experiment and find what you like. Generally set the amount between 50% and 150%, the radius between 1-4, and the threshold between 3-20.

Suggested Settings: Possible starting points (these will differ from photo to photo and be dependent on the photo's size, resolution and so on)

General
Amount 150%, Radius 1, Threshold 3

Soft Subjects
Amount 150%, Radius 1, Threshold 10 (works well for images of a softer nature like people and flowers)

Maximum Sharpening
Amount 65%, Radius 4, Threshold 3 (works well on out of focus photos, or photos that have a lot of well defined edges like buildings)

All-purpose Sharpening
Amount 85%, Radius 1, Threshold 4

Web Sharpening
Amount 400%, Radius 0.3, Threshold 0 (good for blurry web graphics)

Lighter Web Sharpening
Amount 200%, Radius 0.3, Threshold 0

[T Paul]

Always sharpen at 100%

Experiment with selective sharpening vs sharpening the entire image

Sharpen your image as the very last step and avoid resizing or retouching after you have sharpened

Experiment with applying USM to individual channels

Convert your image to Lab Mode and sharpen only the L channel

NOTE: Running USM more than once at a lower amount can sharpen more smoothly than running it once at a setting twice as high.

[T Paul]

TECHNIQUES: There are a lot out there. Here are a few I found while searching the web

[T Paul]

The greatest problem with USM is that it can produce color halos along high contrast edges, especially if you over sharpen. A remedy for this is to use the Edit/Fade command set to Luminosity right after applying the USM to make sure the sharpening affects the luminosity only and not the color in the image.

[T Paul]

In this technique you take a History snapshot before and after using the USM filter. Then use the History Brush tool to paint back and forth between the sharpened and unsharpened snapshots.

NOTE: Alternative technique is to use a layer mask

[T Paul]

This method allows you to sharpen edges and not noise, pores, or out of focus areas. What you do is use the Channels palette to create an "edge mask" which isolates the edges of the image so you can create a selection out them for using the USM. Note, this technique is rather long so you may want to create an action for it.

1. Duplicate the original.

2. Go to Channels palette and find the channel with the most contrast, duplicate it as an alpha channel and name it Edge Mask.

3. Select Filter/Stylize/Find Edges on the alpha channel. Invert the image (Comm/Ctrl - I) so you have white edges on a black background. The white edges will determine the eventual selection.

4. Select Filter/Noise/Median with value of 1 or 2 to accentuate the edges.

5. Select Filter/ Blur/ Gaussian Blur with value of 2 - 4 to "feather" the eventual selection. The blurring will get rid of noise as well as well as prevent unnatural looking transitions between sharpened and unsharpened areas.

Bruce Fraser: "High-resolution images typically require a higher-radius blur than low-resolution ones, and close subjects with soft detail, such as head shots, typically need a higher radius than high-frequency images with lots of fine detail."

6. Return to Composite view (Comm/Ctrl - ~) and Load the alpha channel as an "edge mask" selection (Comm/Ctrl - click the channel).

7. Now use the Unsharp Mask filter on this selection of just the edges of the image.

You can also download an action to automate this smart sharpening process and/or fine tune the action to your own needs.

Actions
Smart Sharpening by John Brownlow

Smart Sharpening by Ben Bardill

[T Paul]

Duplicate the original image twice and use one to sharpen the highlights and the second to sharpen the shadows.
Then use the Blend If layer options to blend the two layers.

[T Paul]

This method is supposed to avoid color shifts when using the USM. Convert the image to LAB mode and use the Unsharp Mask filter on the L (Luminosity) channel.

For portraits, flower shots, and things of a softer nature use amount 150, radius 1 and threshold of 10 for a starting point.

For objects that have well defined edges use amount 65, radius 3 and threshold 2 or amount 65 radius 4, and threshold 3 for a starting point.

Then convert back to RGB. There is some difference of opinion about whether you can shift modes like this and not introduce "quantization errors" from the switch.

[T Paul]

This is a summary of a tutorial by Bruce Fraser which is a variation of the High Pass Sharpening technique in that it involves creating an edge mask from a grayscale version of the image to isolate the effect of the USM. The idea that when you sharpen an image you may cause highlights to become too white and lose detail for printing. So he suggests a two stage process, first a mild sharpening with an edge mask, and then sharpening for the specific output, offset, inkjet, etc.

First pass - a mild sharpening to compensate for the effects of digitalization.
1. Duplicate image.

2. Convert the duplicate to grayscale using the method of your choice. (See summary of techniques on this site).

3. Run Filter/ Stylize/ Find Edges.

4. Run a Filter/ Blur/ Gaussian Blur to help get rid of noise and soften the transitions between sharpened and unsharpened images. Invert the image so the edges are white.

5. Use Levels adjustment to exaggerate the contrast and make sure edges are white and noise is pure black. You want to make sure there is still some gray for the eventual "feathering" of the selection.

6. Load the mask as a selection. Hide the marching ants of the selection with Command/Ctrl - H, and run the Unsharp Mask filter with something Radius .4, Amount 120%, and Threshold 0. You just want an mild sharpening to compensate for original digitization with this first pass.

Second pass - Sharpen the entire image for the particular output device.

[T Paul]

It may be that sharpening just one channel is enough to improve the sharpness of the image.

[T Paul]

This technique uses the USM to make slight bumps in image contrast. Just select a low value for Amount (10-25%), a very high value for Radius (200-300 pixels), and a 0 Threshold. This technique can produce a more likeable contrast boost than does the Contrast command. Just be sure to save a version of your image before using this technique (it's not undoable at a later date). You can also perform this action prior to doing a "real" sharpening.

From Sharpening 101

[T Paul]

The idea here is to have a sharpened layer and an unsharpened layer and use a mask and paint tools to control location of sharpening.

Duplicate the image, use the Unsharp Mask filter on the duplicate layer. The upper layer is now sharpened.

Next add a layer mask by Option/Alt clicking the mask button at the bottom of the Layer palette. This creates a Hide All (black) mask. Use a large, soft, white airbrush on the mask to show the sharpening where you want it.

Or: create a Reveal All (white) mask by simply clicking the mask button at the bottom of the Layer palette. Using a black brush will HIDE the sharpening effect where you paint.

[T Paul]

Duplicate image.

Changing the Blend mode to Soft Light produces a gentle sharpening (increase in contrast), while Hard Light produces a slightly harder sharpening.

[T Paul]

Good for slightly out of focus images, and ones with clear lighting direction.

1. Duplicate the image.

2. Use Filter/ Stylize/ Emboss. Set the angle to match the lighting of the image. Set the Height within 2-4. Keep the Amount near 100%.

3. Change the blend mode to Overlay, which eliminates the gray and accentuates the edges. Adjust the Opacity to control the effect.

[T Paul]

(from Steve A.K.A Trimoon )

1. Copy your image and name the new layer sharp 1

2. Go to Filter>Sharpen>Unsharp Mask

Settings: Amount 200, Radius 8, and Threshold 4. Note, this should greatly over sharpen your image but the next step will resolve this.

3. Next duplicate this layer and name the new layer sharp 2.
Set the blending mode for this layer to LIGHTEN, set the layer mode on sharp 1 to darken.

Experiment with the opacity modes for both layers until you are satisfied with the results.

By adjusting these two layers you will sharpen the image and do away with the edge effect caused by the overuse of the Unsharp Mask filter. It doesn’t work with every image, but 80% of the time it does.

[T Paul]

High Pass Filter Sharpening - Optional Layer Mask

Filter turns all non-edge areas to neutral gray but leaves edge intact. This technique is used in combination with the Soft Light or Overlay Blend modes.

1. Duplicate image.

2. Apply the Filter/ Other/ High Pass filter with radius settings of 3-6. Low-frequency images -- those with close subjects and soft detail -- generally require a higher Radius setting than high-frequency images with lots of fine detail.

3. Change the blend mode to Overlay. The neutral tones in the image are eliminated and the edges accentuated. Use the Opacity slider to control the effect. Use Soft Light blend mode for a softer effect. Overlay produces a little more contrast.

4. Add a layer mask (Option/Alt layer mask button at bottom of Layer palette) on duplicated layer with Reveal All to paint back in original image smoothness, or Hide All to paint in sharpness in selected areas.

5. Stack multiple sharpening layers with layer masks to adjust different areas of an image.

[T Paul]

(from Steve A.K.A Trimoon )

1. Copy your image and name the new layer High Pass

2. Go to Filter>Other>High Pass, now the following settings are not set in stone, you can play with them for different results, but for this we’ll use the following. Let’s try a radius of 10. Then set your blending mode for this layer to overlay. Using the Opacity, adjust accordingly.

Sometimes I will create a couple of layer like above, but different adjustments. By turning each layer off & on you see which one gives you the best results for this particular image. I also will adjust for a certain area, say the eyes; and will mask out the rest and delete, which will give you sharp eyes, yet a soft look to the rest of the image. Again using the Opacity adjustment for just the right look.

This above method of using the high pass filter is something that I used a year or so ago and no longer recommend this method except for certain special effects when doing artistic renderings. Below is a link to the method that I now use, which uses the custom filter. I think you will find it a much better way of doing things. It applies a slight blur to the image before sharpening. After a while, you get to where you are so good at it that you do it intuitively.

Better Than USM

[T Paul]

Books

Adobe Photoshop 7 Advanced Digital Imaging by Against the Clock

Photoshop 7 Wow! Book by Linnea Dayton & Jack Davis

Photoshop Restoration & Retouching (2nd Ed.) by Katrin Eismann

"Out of Gamut: What You Always Wanted to Know About Sharpening But Where Afraid to Ask", two internet tutorials by Bruce Fraser

Photo Re-touch Secrets by Scott Kelby

The Photoshop book for digital photographers by Scott Kelby

Good RetouchPro Threads:

Smart Sharpening

Sharpening using Photoshop (Something Different)

Sharper Images

Good Links:

Understanding Digital Unsharp Mask

Sharpening and USM

Sharpening Techniques

Photoshop High Pass Filter

Everything You wanted to Know about Sharpening

Tutorials

Smart Sharpening Tutorial

Bruce Fraser Two Pass

Glenn Mitchell tutorial on sharpening

Advance Sharpening Movie by Russel Brown

Better than USM

[Mosha]

Are you a teacher...?

Thanks for this wonderful explanation.
Taking advantage on your knowledge... can you do the same thing but for channels...I just don't get them. The more I try to understand them, the more I get confused...

Congratulations

Mosha

[T Paul]

Not a teacher, but I am self-taught so I am pretty good at searching the web or my books for information. As you can see from my resources I gathered this information from all over the net. I find it nice to have all the information at your fingertips.

I'll add channels to my list of things to do.

~T

[Mosha]

What can I say....just... THANKS...

[W. Rose]

Great Job T. Paul,
This has really helped me alot.

[T Paul]

Glad to hear that this is helpful!

If anyone else has a sharpening technique or favorite USM setting I didn't include, please feel free to add them.

[byRo]

Originally Posted by T Paul

(from Steve A.K.A Trimoon )
This above method of using the high pass filter is something that I used a year or so ago and no longer recommend this method except for certain special effects when doing artistic renderings.
..........
Better Than USM

I saw this yesterday in the other thread ('something different') and went running to the link. I was planning to spend the weekend (wife permitting) immersed in convolutions and filter factories.

But..
Can anybody give us a jump start on the learning curve?
Is it better than USM? If so, when and how?
Is it better than high-pass? If so ,when and how?
Use custom filter, or filter factory, or something else?
etc??

Roland

[T Paul]

Excellent question, but one I can't answer. Perhaps someone else will be able to.

Here is a quick low down on the three filters:

From the PhotoShop help file:

Custom Filter

Lets you design your own filter effect. With the Custom filter, you can change the brightness values of each pixel in the image according to a predefined mathematical operation known as convolution. Each pixel is reassigned a value based on the values of surrounding pixels. This operation is similar to the Add and Subtract calculations for channels.

You can save the custom filters you create and use them with other Photoshop images.

To create a Custom filter:

Choose Filter > Other > Custom.
Select the center text box, which represents the pixel being evaluated. Enter the value by which you want to multiply that pixel's brightness value, from -999 to +999.

Select a text box representing an adjacent pixel. Enter the value by which you want the pixel in this position multiplied.

For example, to multiply the brightness value of the pixel to the immediate right of the current pixel by 2, enter 2 in the text box to the immediate right of the center text box.

Repeat steps 2 and 3 for all pixels to include in the operation. You don't have to enter values in all the text boxes.

For Scale, enter the value by which to divide the sum of the brightness values of the pixels included in the calculation.

For Offset, enter the value to be added to the result of the scale calculation.
Click OK. The custom filter is applied to each pixel in the image, one at a time.

Use the Save and Load buttons to save and reuse custom filters.

High Pass

Retains edge details in the specified radius where sharp color transitions occur and suppresses the rest of the image. (A radius of 0.1 pixel keeps only edge pixels.) The filter removes low-frequency detail in an image and has an effect opposite to that of the Gaussian Blur filter.

It is helpful to apply the High Pass filter to a continuous-tone image before using the Threshold command or converting the image to Bitmap mode. The filter is useful for extracting line art and large black-and-white areas from scanned images.

Unsharp Mask
The Unsharp Mask does not detect edges in an image. Instead, it locates pixels that differ in value from surrounding pixels by the threshold you specify and increases the pixels' contrast by the amount you specify. So, for neighboring pixels specified by the threshold, the lighter pixels get even lighter and the darker pixels get even darker based on the specified amount.

In addition, you specify the radius of the region to which each pixel is compared. The greater the radius, the larger the edge effects.

A while back there was a discussion on the Custom Filter in this thread

Also here are some web links that may be helpful if you want to tackle convolutions

Convolution Web Links
Creating Custom Filters Photoshop Tutorial

Convolution Corner

Convolution Kernels

Custom Image Filter

Home-made effects: Creating your own filters - lots of info here

[kbeatrice]

Hi T. Paul, this is a great summary of sharpening methods! In the layer mask section I think that you might have accidentally swapped the brush colors:

Next add a layer mask by Option/Alt clicking the mask button at the bottom of the Layer palette. This creates a Hide All (black) mask. Use a large, soft, black airbrush on the mask to show the sharpening where you want it.

Or: create a Reveal All (white) mask by simply clicking the mask button at the bottom of the Layer palette. Using a white brush will HIDE the sharpening effect where you paint.

Did you mean white airbrush on black for the first one and black brush on white for the second one?

Thanks again for the great summary!

[byRo]

Originally Posted by T Paul

Also here are some web links that may be helpful if you want to tackle convolutions..........

Wow, who needs Google when T Paul's around!

Didn't find much in the way of answers, did find a whole bunch of questions....
Seems like I'm going to be pretty bleary-eyed come Monday.

thanks,

Roland

[T Paul]

Originally Posted by kbeatrice

Hi T. Paul, this is a great summary of sharpening methods! In the layer mask section I think that you might have accidentally swapped the brush colors:

Ooops! Thanks for catching that. That post has been corrected.

[T Paul]

Originally Posted by byRo

Wow, who needs Google when T Paul's around!

Didn't find much in the way of answers, did find a whole bunch of questions....
Seems like I'm going to be pretty bleary-eyed come Monday.

thanks,

Roland

Yes the whole convolution thing is rather confusing. I think the best plan is to use some of the examples and start experimenting on your own.