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

Home > Articles

Image Editing Basics

This chapter is from the book

Correcting Tone and Contrast with Curves

If you're using Photoshop 7, CS, or CS2, then you have access to Curves, another type of tone and contrast correction tool. Curves allows you to do the same thing as Levels—brighten and darken the pixel values of your image—but it uses a very different interface ( Figure 3.20 ).


Figure 3.20 The Curves dialog box shows an interactive graph with original tones represented by the horizontal grayscale ramp, and adjusted tones represented by the vertical grayscale ramp.

First off, notice that unlike Levels, Curves does not provide you with a histogram display. If you're using Photoshop CS or CS2, then you can use the Histogram palette to watch your image's histogram while you edit.

Next, notice that there are two grayscale ramps: a horizontal one across the bottom, and a vertical one running up the side. The horizontal ramp is the input scale, and it represents the values in your image before the Curves adjustment. The vertical ramp is the output scale, and it represents the values that your image will have after the adjustment. The diagonal line through the center of the box shows the correspondence of the input scale to the output scale. This line is your curve, though when you first open the Curves dialog box, the curve is straight.

When you open Curves, if you trace a line from a gray tone on the input scale up to the curve, and from there directly across to the output scale, you'll see that the input tone corresponds to an identical output tone. In other words, the curve is not changing the value of the tone ( Figure 3.21 ).


Figure 3.21 Reading the Curves dialog box is very simple. For any particular original, or input tone, just trace a line up to the curve and over to the output graph to see what that tone will be after the Curves edit is applied.

By reshaping the curve, you can remap the input tones to new output values. To change the shape of the curve, you simply click it and drag. This will add a new control point in addition to the two on the ends. The curve is redrawn to pass through this new point.

For example, if you click the middle of the curve and drag straight up, you will create a new control point and reshape the curve. Now go back to the input tone you looked at before and trace a line up to the curve and then over to the output scale, and you'll see that that tone is lighter ( Figure 3.22 ). Most important, all of the surrounding tones have been adjusted to create a smooth transition.


Figure 3.22 Dragging the curve upward causes the original tone to be remapped to a lighter value. All of the tones around that value are remapped to create a smooth transition.

Curves actually does the same thing as Levels. The lower-left control point on the curve is the same thing as the black point in the Levels dialog box. Similarly, the upper-right point on the curve is equivalent to the Levels white point. When you add a point to the middle of the curve, you get a gamma control.

So to use Curves to perform the same correction that you saw in Figure 3.12, you would define a curve that looks like Figure 3.23 .


Figure 3.23 The end points of the curve allow you to change the black and white points of the image, just as the black and white control points in the Levels dialog box do.

The main advantage of Curves over Levels is that whereas Levels lets you adjust only 3 points, Curves lets you add up to 14 control points. By adding more points, you can brighten or darken selected portions of your image.

Although the gamma adjustment in Levels offers a great way to change the midtones of an image without affecting the white and black points, there are times when you won't want to adjust all of the midtones equally.

For example, Figure 3.24 shows another image that could use more contrast. Although we could increase the contrast by moving the white and black points inward, we would clip both the highlights and the shadows. With Curves, we can leave the white and black points where they are and apply separate adjustments to the middle of the curve.


Figure 3.24 Applying an S-curve to this image improves the contrast of the image by darkening some of the shadows while brightening the highlights. Notice that the black and white points are left untouched, so you don't have to worry about clipping.

The lower point on our curve darkens the shadows, while the upper point brightens the highlights. The overall effect is to give a big contrast boost to the image, without hurting the shadows and highlights. In most cases, adding a slight S-curve edit like this to an image will improve its contrast.

Making selective corrections

The ability to add multiple control points means that you can target Curves to adjust very specific parts of your image. For example, overall Figure 3.25 is well exposed. However, when this image is printed on glossy paper, the already dark house becomes much darker.


Figure 3.25 Though this image is generally well exposed, the barn becomes too dark when the image is printed. With a Curves adjustment, it's possible to lighten the barn while leaving the rest of the image untouched.

Ideally, you want to lighten the house without adjusting any other parts of the image. There are many ways to achieve this type of edit in Photoshop. You could select the house using the Pen or Lasso tool and apply an adjustment to only that selected part of the image, or you could use an adjustment layer with a layer mask—the list goes on and on.

With Curves, though, you can constrain the adjustment to only the house by editing only the part of the curve that contains the tonal values that make up the house.

With the Curves dialog box open, you can click anywhere in your image, and a small circle will appear over the curve to indicate the tonal value of the pixel you clicked. So if you click the barn, you see that its tones live in a very particular part of the lower-left end of the curve ( Figure 3.26 ).


Figure 3.26 With the Curves dialog box open, you can click within your image to see where particular tones lie on the curve.

To adjust only that part of the curve, you first "lock down" the rest of the curve by adding control points. These will serve as anchors to prevent other areas of the curve from being affected by your edit ( Figure 3.27 ).


Figure 3.27 To edit just one part of the curve, you first anchor the curve by placing a few control points.

Now you can simply drag the barn part of the curve up to create your edit ( Figure 3.28 ).


Figure 3.28 With the curve anchored, it's possible to edit just the area that contains the tonal values of the barn. With this edit, the barn brightens while the rest of the image remains the same.

Like Levels, Curves becomes much easier to use with practice. With just a little experimentation, you'll get a better feel for how to drag and shape the curve. Be careful, though—even a slight reshaping of the curve can create a big adjustment to your image. Keep your eyes peeled for posterization (the reduction of tones that can turn some transition areas into splotchy masses of solid color), especially if you're targeting a specific area where there aren't a lot of tones, such as deep shadows or highlights. A sudden or steep change in the curve will almost always yield posterizing. Try to keep the bends in your curve gentle.

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.


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.


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.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email

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.


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


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


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 and we will process the deletion of a user's account.


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:

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

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.


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