Publishers of technology books, eBooks, and videos for creative people

Home > Articles > Adobe Photoshop > Technique

Real World Image Sharpening Tips From Expert Bruce Fraser

Avoid oversharpening your images and learn how to set up a multipass sharpening workflow in Adobe Photoshop CS2 in this excellent sample chapter from best-selling author Bruce Fraser.
This chapter is from the book

This chapter is from the book

In the last chapter, we saw that sharpening has to take into account several different and often contradictory demands. In this chapter, I'll offer a means of reconciling these disparate demands, while pointing out the potential pitfalls in doing so.

Having tried for decades to meet all the requirements imposed by image source, image content, and image use in a single sharpening operation, I've reluctantly concluded that it is in fact impossible to do so. Of course, this conclusion flies in the face of conventional wisdom, which dictates that sharpening should be applied in a single pass as either the last or next-to-last step (before conversion to final CMYK in an RGB workflow) in the image reproduction chain. But the conventional wisdom does have some foundation.

  • Back when the drum scanner was king, images were usually scanned directly to CMYK, at reproduction size, with sharpening applied by the scanner. The conventional wisdom workflow tries to replicate this.
  • If downsampling is done after sharpening, the image has to be resharpened, because the haloes get downsampled out of existence.
  • Multiple passes of sharpening tend to ruin images.

    These are all good points that deserve careful consideration, but let's look at the downsides to the conventional wisdom.

Traditional Prepress Sharpening

First, let's be clear that traditional sharpening works reasonably well as long as it's done with the requisite skill and the built-in assumptions aren't violated. But there's a substantial difference between "reasonably well" and "optimally."

In the traditional sharpening workflow, sharpening is applied either as the final process (which allows tricks like sharpening only the black plate, so that eyelashes and hair get sharpened, but skin textures don't), or as the next-to-last process before conversion to final CMYK. It offers a simple workflow (which is no small advantage), but it also has its share of disadvantages.

One-Pass Sharpening is Inflexible

A key assumption in the traditional sharpening workflow is that the final use is known, and the image has been sized for that final use. Back in the rubylith days, this assumption was generally valid, but as soon as page layout applications gave designers the ability to resize images in the layout, that assumption went out the window.

Nowadays, it's common practice for prepress operations to act both as suppliers of original scans, and as the final step in the output chain. As a result, it's not uncommon for scanned images to receive two rounds of sharpening, once at the time of the scan on the high-resolution image, then again on the resized image before output. The key point is that traditional sharpening is designed to be applied to the final image at final output resolution, and the further the image is from that state, the less successful the sharpening is likely to be.

One-Pass Sharpening is Often Overdone

Since traditional sharpening, as it is commonly use today, is sensitive neither to image content nor to final use, it's common to see grossly over-sharpened images, especially in the case where a sharpened scan receives a second round of sharpening at final output size.

Figure 3-1 shows an image scanned without sharpening, then sharpened carefully in two passes, and the same image sharpened during the scan, then again after resizing.

fig3_1a.jpg

Figure 3-1 Oversharpening

While this kind of oversharpening is rare in high-end work (because someone has paid to make sure that it doesn't happen), it's depressingly commonplace in commercial publishing. However, this is not an argument against multi-pass sharpening: Both versions of the image in Figure 3-1 received two sharpening passes. Rather, it's an argument against careless sharpening that fails to account for image content and final use.

One-Pass Sharpening and Digital Capture

Traditional one-pass sharpening is very much tailored to scanned transparencies, since it essentially simulates the sharpening built into drum scanners. (It's possible to get good drum scans from color negative, but relatively few operators know how to do so.)

Traditional Sharpening is Global

A salient feature of traditional sharpening is that it's applied globally to the entire image. While this worked reasonably well with transparency scans, it generally fails to do justice to digital raw captures, where it sharpens the noise along with the edges.

The problem becomes worse when global sharpening is also applied by the conversion software that translates the raw camera capture into a rendered RGB image. (Bear in mind that when you shoot JPEG, the camera itself performs a raw conversion, often with sharpening applied as default.) Figure 3-2 shows a range of possibilities from a digital raw capture.

fig3_2a.jpg

Figure 3-2 Digital raw capture

Most raw converters offer the option to produce an unsharpened image, but many photographers decline to exercise this option because the results are obviously soft on the display. Yet many of the major stock agencies specify that submissions should be unsharpened. This is a recipe for soft images.

Global sharpening in the raw converter followed by traditional sharpening produces images with sharp noise, but not necessarily with sharp detail. The two-pass sharpening used on the image at the bottom of this page accounts for image source and content, producing the best result.

Traditional Sharpening Fails to Exploit Digital Capture

By its nature, digital capture, unsharpened, produces images that both tolerate and require a good deal more sharpening than those from film. Most digital cameras actually include an optical low-pass filter to prevent color artifacting, which has the effect of softening the image. As a result, traditional sharpening, which is optimized for transparency scans, often undersharpens digital captures. Figure 3-3 shows the difference between a traditionally sharpened and an optimally sharpened digital raw capture.

fig3_3a.jpg

Figure 3-3 Digital raw capture and undersharpening

This failure to understand the inherent properties of digital capture and the differences between digital capture and scanned transparencies has given rise to a considerable body of prepress myth regarding the perceived superiority of film over digital capture. But like it or not, digital capture has already largely replaced film for most commercial work, and the trend is clear and irreversible.

Traditional Sharpening Roots

Traditional sharpening is rooted in the drum scanner, and, moreover, in the analog drum scanner. The earliest drum scanners, from the 1960s, were analog devices that produced actual CMYK film separations, and the sharpening was done optically. By the 1980s, drum scanners produced digital CMYK files, still with optical sharpening.

When the desktop revolution hit in the early 1990s, the old paradigm of scanning at final resolution for a specific use fell by the wayside. Photoshop 2.0 introduced CMYK support, and changed print manufacturing forever, though not overnight—proprietary systems from the likes of Scitex, Linotype-Hell, Crosfield, and Agfa continued to hold sway for much of the decade, but by 1999, Photoshop had become not only a ubiquitous noun, but also a verb.

Photoshop Sharpening Practice

As has often been the case when an analog process is replaced by a digital one, most practitioners of sharpening in Photoshop used Photoshop's sharpening tools to replicate the drum scanning workflow. There is still considerable debate as to whether to sharpen before or after conversion to CMYK (some even advocate converting to Lab and sharpening the Lightness channel), but it's generally agreed that sharpening must be done at the final output size and resolution, after all major tonal adjustments have already been performed.

Traditional Sharpening Problems

The main problem with the traditional sharpening approach is that it tries to account for image source, image content, and output process in a single round of sharpening. After 15 years of experience using Photoshop to produce images both on press and on desktop printers, I concluded that it's simply impossible to address all three factors in one sharpening pass. The preceding pages of this book show the kinds of problems that arise when we attempt to do so. While the results aren't invariably bad, they're never as good as they could be.

Multipass Sharpening Problems

Many Photoshop users have at some point tried a multipass sharpening approach. A few have made it work, but the vast majority have wound up creating grossly oversharpened images, usually by falling into one or more of three potential pitfalls.

  • Relying on the computer display to judge sharpness is a practice fraught with peril, yet until we make the print, it's all we have. The temptation is to make the image look sharp on screen, then to sharpen it again for output, often with unacceptable results.
  • Failure to take image content into account in the first round of sharpening typically results in applying the wrong kind of sharpening for the image, so wanted detail may be obscured and unwanted detail or noise may be exaggerated.
  • Applying the first pass of sharpening globally rather than through a mask that isolates edges sharpens noise and flat textured areas such as skies as well as sharpening the edges. When the second pass of sharpening is applied, the image becomes oversharpened.
  • Applying the first pass of sharpening to the entire tonal range, rather than protecting the extreme highlights and shadows, almost guarantees that the second pass of sharpening will create blown highlights and plugged shadows.

The good news is that all of these problems are avoidable given sufficient attention, care, and skill. Building a multipass sharpening workflow is not a trivial undertaking, but neither is it impossible—otherwise I wouldn't have bothered writing this book!

Peachpit Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Peachpit and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Peachpit products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email ask@peachpit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.peachpit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020