refraction73_MG_1171

High frequency

refraction74_20100809__ICEjokulsarlon_0148

Medium Frequency

refraction6420080816_iceland_reykjanes_0496

Low Frequency

Frequency is a term that’s being used more and more. That’s because new tools offer you more control over frequency than ever before. Noise reduction, sharpening, and HDR all offer unprecedented control over the look and feel of detail in our images. Frequency is used to describe the amount of detail packed into a given area of an image. This is measured by the amount of tonal variation between rows or columns of pixels. Imagine measuring an image with a line that passes across it (horizontally from left to right or vertically from top to bottom). The mean or average tonal value along lines can be charted and then compared to values from other measurement lines, especially those nearest to each other.

In high frequency images you’ll find a great deal of variation between measurements; many lines, thick and/or thin, and lots of texture, coarse and/or fine, rendered with high contrast.

In medium frequency images you’ll find a modest amount of variation between measurements; clear contours with moderate to low amounts of texture in between.

In low frequency images you’ll find very little variation between measurements; characterized by smooth long gradations, often with reduced contrast or flat fields of color.

Many images contain a combination of high, medium, and low frequencies. When enhancing images you can choose to emphasize the dominant frequency or selectively enhance areas with different frequencies for even greater precision. Some software features provide ways to target these frequencies as you adjust them. When software doesn’t provide ways to target frequency, you can design an effect for that image area on a separate layer in Photoshop and mask it from other areas you don’t want to be treated in the same way.

In many cases, you don’t need to measure an image to decide what tack to take. By looking at an image with a discerning eye you’ll quickly be able to tell if and where an image contains high, medium, and/or low frequencies.

Simply being aware of and sensitive to frequency in images will encourage you to be more precise with your image adjustments. With a little extra care your images will all become stronger.

Read more about sharpening here.

Learn more in my digital photography and digital printing workshops.

Refraction LXIX 2

Of the three stages in a sound sharpening workflow – capture sharpening, creative sharpening, and output sharpening – creative sharpening is the stage that has the most impact.

The goal of creative sharpening is to give an image a specific look and feel. There are at least three things creative sharpening can do for your images. One, creative sharpening can prioritize; it can direct attention to specific areas of an image. Two, creative sharpening can enhance; qualitative aspects of images like texture and line, can be amplified to produce stronger responses. Three, creative sharpening can be used to accentuate different qualities of light; a great deal of detail is carried by the luminosity component of color and changing it changes the overall appearance of light within the image. Used consistently creative sharpening can produce a distinctive style that is more easily recognizable to viewers. (Remember, sharpening is a way to enhance details and it may also be used with its counterpart blurring to make effects appear even stronger by comparison.)

The decisions made during creative sharpening are largely subjective and based on the visual preferences of the individual doing the sharpening, not the characteristics of the tools used to produce an image. When performing creative sharpening there are essentially no rules. Only the image source, the software you choose to use, and, most importantly, your aesthetic sensibilities will determine the limits of how far you can go. If there are limits to how far you should go, those limits are only determined by consensus; in general most viewers don’t want to be distracted unnecessarily by sharpening artifacts – unless they are an integral part of the statement an image makes. During creative sharpening you can leverage any and all sharpening techniques. Creative sharpening can be as simple or as sophisticated as you choose. Increasing your sharpening skills will lead to enhancing your expression. The final determining factor during creative sharpening is that it creates a desired visual appearance.

Creative sharpening needs to be determined visually, while previewing an image on a monitor at 100% screen magnification, the magnification that most precisely displays low frequency detail such as texture and noise.

Creative sharpening is done after Raw conversion that includes conservative capture sharpening, typically in Photoshop, employing additional image layers, with masks. Creative sharpening is most frequently applied selectively, varying the amount and/or type (Clarity, High Pass, Unsharp Mask, Smart Sharpen, etc) of sharpening in different regions of an image.

While there are no standard formulas for creative sharpening that will apply equally well for all images and more importantly all users, this doesn’t mean you can’t automate many parts of creative sharpening, once you’ve created a sharpening recipe that pleases you. Recording your preferred sharpening routines as actions can speed up this process. It does mean that to get it really right you’ll want to modify the results of your recipes based on the characteristics individual images you’re processing – sometimes subtly and sometimes substantially.

Creative sharpening may need to be removed and reapplied if an image file is dramatically upsampled, as the resampling process can make sharpening artifacts not visible at smaller scales more pronounced at larger scales and in some cases exaggerate them.

Not all images need to be creatively sharpened. In high productivity workflows, where large volumes of images need to be processed quickly, creative sharpening is typically abandoned because it can’t be fully automated. But ‘hero’ images are another matter entirely. The images you care most about deserve creative sharpening – and for these it can make all the difference in the world.

Follow up with How To Avoid Common Over-Sharpening Artifacts.

Read more about sharpening here.

Learn more in my digital photography and digital printing workshops.

1_sharp_refraction_LXXIII1 copy

2_sharpenedlayerstack copy

Layers have Blend Modes and can be masked

3_layerstyle copy

Double click a layer to activate its Blend If sliders  

There are many reasons to use layers when sharpening your digital images.

How do you do this? Simply duplicate the Background layer and sharpen the new layer.

Eliminate Saturation Shifts

Layers can be used to eliminate saturation shifts. Change the Blend Mode of a sharpening layer from Normal to Luminosity. Color noise will also be reduced this way.

Prevent Clipping

Layers can be used to prevent clipping in deep shadow detail (near-black) and bright highlight detail (near-white). As sharpening is a contrast effect, near-white and near-black values can be driven to pure white and pure black by it. There’s a cure. Double-click the layer to activate Layer Styles. Use the Blend If sliders to reveal the lost highlight and shadow detail in the background layer below the sharpening layer; zoom way into a highlight area, hold the Option/Alt key and drag the right arrow to restore highlights and the left arrow to restore shadows.

Precise Local Adjustment

Layers can be masked for greater control over confined areas in an image. To begin, add a layer mask. Select an area from which you wish to remove a sharpening effect, like a sky or other area of even tone, and fill the area with black. You can use this strategy to remove unwanted texture or noise from selected areas of an image. Gray values can be created on a mask with the Gradient tool or with a Brush tool to gradually reduce a sharpening effect. This often can produce a more strongly felt impression of space within an image. In anticipation of selectively modifying an effect, you may decide to sharpen an image more aggressively.

One approach to gaining additional flexibility with sharpening effects is to set a sharpening layer to 50% Opacity before applying the filter and then later adjust the opacity up or down to get more or less of the effect. This can be useful, but be mindful of its limitations. Reducing or increasing a sharpening layer’s opacity will provide an effect similar to adjusting Amount; more or less contrast is added. But modifying opacity can’t simulate the effects of different Radius settings—thicker or thinner contours.

Combine Multiple Types Of Sharpening

Use more than one duplicate layer and you’ll be able to combine multiple types of sharpening by simply reducing the top layer’s opacity. Unsharp Mask, High Pass, and Clarity all produce different effects that can be combined into still new effects. With these tools, you can craft a unique look and feel for detail in your images.

In addition to the flexibility of changing and/or removing and remaking sharpening effects layers’ features Blend modes, Blend If sliders, Opacity, and Layer Masks offer extraordinary control and precision. When you want to get sharpening effects really right, use layers.

Read more on sharpening here.

Learn more in my digital photography and digital printing workshops.

Adams_Ross_425

Ansel Adams and Imogene Cunningham by Alan Ross

Check your inboxes!

My newsletter collects great resources on photographer Ansel Adams.

Sign up here.

01_CaptureSharpen

02_CaptureSharpen
Adobe Camera Raw’s Detail panel

Optimal image sharpening is best done in three stages – capture (Do it during Raw conversion.), creative (Do it in Photoshop.), and output (Automate it.).

This article covers the first stage of sharpening – capture sharpening.

Capture sharpening benefits all images. Capture sharpening compensates for inherent deficiencies in optical and capture systems. All lenses and sensors have specific characteristics and deficiencies. They do not all have the same characteristics or deficiencies.

To speed your workflow, default settings for a best starting point for capture sharpening can be determined for all images created with the same lens/chip combination and saved for subsequent use. To optimally sharpen an image, you’ll need to modify these settings to factor in additional considerations – variances in noise (ISO, exposure duration, temperature), noise reduction settings, and the frequencies of detail (low/smooth to high/fine texture) in an image.

Capture sharpening is determined visually. Perform capture sharpening while previewing an image on a monitor at 100% screen magnification, the magnification that most precisely displays high frequency detail such as texture and noise.

Capture sharpening is best done during Raw file conversion. (Do it after scanning for analog originals.) I recommend importing your Raw files into Photoshop as Smart Objects. If you do this, you can quickly access specific sharpening and noise reduction settings simply by double clicking the image layer. At the same time, you’ll also be able to take advantage of any updates in detail rendering (noise reduction and sharpening) with the click of a button. (Do be mindful that any adjustments you make in Adobe Camera Raw will not be recorded in a Lightroom library.)

Capture sharpening is typically done globally and uniformly to all areas of an image, but on the fly masking routines are recommended for reducing and removing sharpening effects, such as halos on contours and noise in low frequency or smooth image areas.

When performing capture sharpening, err on the conservative side and avoid producing unwanted artifacts. Don’t fall prey to the temptation to fix unwanted sharpening artifacts you could produce at this first stage of sharpening in subsequent stages of image editing; you’ll get better results if you don’t produce unwanted sharpening artifacts at all. Additional sharpening enhancements can be performed locally with more precision in Photoshop during creative sharpening.

Set Clarity before sharpening. It produces a different but related contour contrast. If you change Clarity settings substantially, double check your sharpening settings

Perform noise reduction before capture sharpening. You’ll use slightly more aggressive sharpening settings to compensate for the blurring noise reduction introduces. As with capture sharpening, produce as few artifacts as possible during noise reduction. If you need to perform more aggressive or localized noise reduction, do it in Photoshop. (See my noise reduction series on digitalphotopro.com.)

03_CaptureSharpen

04_CaptureSharpen

Lightroom’s Detail panel

The Detail controls in Adobe Camera Raw and Lightroom are identical; only their appearance varies.

There four Sharpening sliders.

1          Amount controls the contrast of the effect produced.

2          Radius controls the width of halos (light) and lines (dark) produced around contours.

3          Detail skews the effect towards a particularly frequency of detail – high, medium, or low.

4          Masking creates on-the-fly edge masks, removing the effect from smoother lower contrast areas. (You can see the mask when you hold down the Option/Alt key and click on or slide the slider.)

Images with high frequency detail benefit from using smaller Radius settings, higher Amount and Detail settings. (And lower Noise Reduction settings.) Images with low frequency detail benefit from using higher Radius settings, lower Amount and Detail settings. (And higher Noise Reduction settings.) Images with a wider variety of frequencies, especially those that containing significant contours, benefit from higher Masking settings.

If you don’t know where to start, start with an Amount of 100, a Radius of 1.0, and Detail of 50. Then adjust with the above recommendations in mind, but above all look critically at the way the effect affects your image.

There will be many times when you will want to readjust Noise Reduction settings after determining Sharpening settings. The two are intimately related.

Finding an optimum balance involves making trade-offs. Again, be conservative and avoid producing artifacts. This is perhaps the hardest part of capture sharpening, as the tools are powerful and the effects can be compelling so the temptation to go too far is great. Resist. Remember, there’s a second stage of sharpening for localized effects – creative sharpening.

Double processing Raw files with Photoshop will allow you to apply different noise reduction and sharpening settings to different areas of an image with great precision. In one version you can aggressively sharpen high frequency detail with little noise reduction, such as textured stone, and in second version you can minimally sharpen low frequency detail with high noise reduction, such as a clear blue sky. When you do this, you can optimize sharpening settings for one frequency of detail and ignore the artifacts produced in another. With detail settings optimized for different frequencies on separate layers in Photoshop, you can mask the suboptimal areas in the overlying layer and reveal the optimal detail in the layer below. (Here’s an easy way to do this. First, import the first version into Photoshop as a Smart Object. Second go to Layer : Smart Objects : New Layer Via Copy. Third, double click the new Smart Object to change the detail settings in the overlying layer. Note, if you simply Duplicate a Smart Object instead the settings will be reset in both layers. The way you make the Smart Object determines whether the duplicates share the same settings or have different settings.)

Read more in my digital image Sharpening resources.

Learn more in my digital photography and digital printing workshops.

1_Sharpen_No

No sharpening.

2_Double_USM

Double pass Unsharp Mask sharpening.

4_Hybrid_HighPass

Hybrid Unsharp Mask and High Pass sharpening.

Different sharpening techniques make the world look different. A world of difference can be seen between the thin hard line of Unsharp Mask and the broad feathered line of High Pass Sharpening.

Can you choose a combination of both? Yes you can! You can choose the texture of one, the halo of another, and the line of yet another, applying them either globally or selectively. You can customize the look and feel of detail in any image or image area with astonishing precision and flexibility.

2_Double_USM

2b_Sharpen_DoublePass

Double Pass Sharpening

Results will differ if you filter the same image layer twice. Why? First, either the technique or the settings can be varied. Second, having been filtered once, the state of the pixels will have changed before a second pass is applied, generating a different final effect. Consequently, not only the type and amount of filtration matters, but also the order in which the filtration is applied.

One classic double pass sharpening technique involves filtering first with an Unsharp Mask setting using a low Radius (under 1.0) and a high Amount (300% or more) and second with an Unsharp Mask setting using a high Radius (approximately1.5) at an Amount of 100%. A variant of this technique adds a third pass of High Pass sharpening. Both methods use the first pass of Unsharp Mask to give the second pass of filtration more to bite into. The key to making any multi-pass sharpening technique successful is to produce a strong yet still convincing effect with as few, if any, unwanted artifacts as possible, either with or without masking.

Some routines will repeat filtration at a lower amount multiple times; for instance, a sharpening setting may be applied ten times at ten percent instead of one time at one hundred percent. The idea behind this approach is that you can achieve a more intense effect (crisper edges) with fewer artifacts (accentuated noise/texture). As it’s inefficient to perform these routines by hand more than one time, this type of approach is best handled by recording an Action that you can play for future uses, which may need to be modified if resolution varies substantially.

Are there benefits to filtering more than twice on the same layer? Maybe. Maybe not. You get diminishing returns with each additional pass of filtration. You may also run the risk of producing more unintended artifacts. Furthermore, as complexity rises your ability to both predict and interact with the final effect diminishes. In general, I recommend you be cautious of highly complex routines and urge you to ask yourself if you derive significant benefit from them.

4_Hybrid_HighPass

3b_Sharpen_Hybrid

Hybrid Sharpening

Sharpening results will also differ if you apply varied filtration techniques to separate layers. Here, the order of the layers in the layer stack matters.

To combine the effects of the different layers use blend modes: Darken will display the only values on a sharpening layer that are darker than values on layers below it, such as the dark line; Lighten will display the only values on a sharpening layer that are lighter than values on layers below it, such as the halo; Luminosity will display any values that change in brightness, but not hue or saturation, and may override any sharpening effects below them so consider separating one Luminosity layer into two layers, one on Lighten and the other on Darken, as their cumulative effect will enhance rather than override underlying effects.

High Pass sharpening layers (or any technique that reduces an image layer largely to gray values) combine easily with other layers using blend modes (typically Overlay); they do this so well that many times it doesn’t matter whether they are placed above or below other sharpening layers.

To reduce file size, you may decide to merge multiple sharpening layers into a single layer. While this makes a file easier to manage now, it reduces your ability to modify the sharpening effect in the future and to clearly track any effects or artifacts were produced. Weigh the pros and cons of this option carefully.

Selective Sharpening

By keeping sharpening effects on separate layers you not only preserve the future flexibility of the effects you create but you are also able to selectively control the effects and target specific areas of an image more precisely. There are three primary ways of doing this; blend modes; Blend If sliders; and masks. A layer’s blend mode controls the way its values combine with values in layers below it; access a layer’s blend mode at the top of the layer stack. A layer’s Blend If sliders let you quickly remove effects from highlights and/or shadow. Activate a layer’s Blend If sliders by double clicking on it – split the sliders for smoother transitions. A layer mask allows you to target different areas of an image. Add a mask to any layer by clicking the mask icon in the Layers palette and fill (either with selection or brush) areas you want to reduce an effect in with varying shades of gray, darker values reduce effects more.

When you combine different sharpening techniques you’ll find that when it comes to the appearance of detail you’ll have a wider variety of choices to choose from. This can affect more than just the look and feel of your images. You can also use it to guide the eye to specific image areas in different ways, producing a qualitatively different visual journey. Sharpening can make the world looks different. Master sharpening and you may even see the world differently. People who view your images certainly will.

Read more in my digital image Sharpening resources.

Learn more in my digital photography and digital printing workshops.


keep looking »

Subscribe

Get the RSS Feed  

Subscribe by Email