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

Home > Articles > Digital Audio, Video

  • Print
  • + Share This
This chapter is from the book

Color Manipulation Building Blocks

Color correction is a somewhat intuitive process. Often compositors just try something until they get it right. Understanding the math behind color correction can help you pick the right tool for the job when you’re attempting to reach a specific result—which is better than trial and error. TABLE 4.1 explains most of these building blocks.

TABLE 4.1 Basic Color Correction Functions

Math Function

Node

Explanation

Names in Nuke

Other Known Names

Add

Add, Grade, ColorCorrect

Adds a constant value to a channel.

Add, offset

Multiply

Multiply, Grade,ColorCorrect

Multiplies the channel by a constant value.

Gain, Multiply

Brightness, Contrast, Exposure, Input/Output White

Gamma

Gamma, Grade, ColorCorrect

Applies a gamma curve to a channel.

Gamma

Contrast

RolloffContrast, ColorCorrect

Applies a contrast curve to a channel. This is also a form of multiplication.

Contrast, RolloffContrast

Lift

Grade

This function is similar to Multiply and Contrast. It’s a contrast curve with a center at white. More later in this chapter.

Lift

Pedestal, Input/Output Black

Lookup

ColorLookup

Applies a user-defined curve to a channel.

Colorlookup

Curves

Saturation

Adjusts the color intensity by reducing the differences between the RGB channels.

Saturation

Dynamic range

When dealing with color correction, I usually talk about dynamic range and its parts. Dynamic range means all the colors that exist in your image, from the darkest to the brightest color. The dynamic range changes from image to image, but usually you are working with an image that has black and white and everything in between. The parts of the dynamic range, as mentioned, are split according to their brightness value as follows:

  • The shadows or lowlights, meaning the darkest colors in the image
  • The midtones, meaning the colors in the image that are neither dark nor bright
  • The highlights, meaning the brightest colors

In Nuke, and in other applications that support colors beyond white and black (float), there are two more potential parts to the dynamic range: the super-whites and the sub-blacks.

Let’s look at these building blocks in several scenarios to really understand what they do and why you might choose one over another.

  1. Launch Nuke.
  2. Bring in a clip called car.png by pressing R and navigating to the chapter04 directory.
  3. Click Read1, then press 1 on the keyboard to view it.

    It’s an image of a car. Did that catch you by surprise?

  4. With Read1 selected, go to the Color toolbox and click Add in the Math folder.

    You have now inserted a basic color-correcting node after the car image. Let’s use it to change the color of the image and see its effect.

  5. In Add1’s Properties panel, click the Color Picker button to display the In-panel Color Picker. Play with the R, G, and B colors to see the changes (FIGURE 4.1).

    FIGURE 4.1

    FIGURE 4.1 Using the In-panel Color Picker

    You can see that everything changes when you’re playing with an Add node—the highlights, midtones, and even blacks (FIGURE 4.2). An Add operation adds color to everything uniformly—the whole dynamic range. Every part of the image gets brighter or darker.

    FIGURE 4.2

    FIGURE 4.2 The whole image is becoming brighter.

  6. When you’re finished, close the In-panel Color Picker.
  7. Select Read1 again and branch out by holding the Shift key and clicking a Multiply node from the Math folder in the Color toolbox.
  8. While Multiply1 is selected, press 1 on the keyboard to view it.
  9. In Multiply1’s Properties panel, click the Color Picker button to display the In-panel Color Picker and experiment with the colors (FIGURE 4.3).

    FIGURE 4.3

    FIGURE 4.3 The changes affect the highlights more than the rest of the image.

    You can see very different results here. The highlights get a strong boost very quickly whereas the blacks are virtually untouched.

  10. Repeat the previous process for the Gamma node. Remember to branch from Read1 (FIGURE 4.4).

    FIGURE 4.4

    FIGURE 4.4 The midtones change the most when you’re changing gamma.

    You can see that gamma deals mainly with midtones. The bright areas remain untouched and so do the dark areas.

    You should now have three different, basic, math-based color correctors in your Node Graph that produce three very different results, as shown in FIGURE 4.5.

    FIGURE 4.5

    FIGURE 4.5 The results from changing Add, Multiply, and Gamma

    Your DAG should look a little like FIGURE 4.6.

    FIGURE 4.6

    FIGURE 4.6 Branching three color correctors from a node

    Let’s try some more color correction nodes.

  11. Select Read1 and then Shift-click RolloffContrast in the Color toolbox to create another branch.
  12. While viewing RolloffContrast1, open its Properties panel and play with the Contrast value (FIGURE 4.7).

    FIGURE 4.7

    FIGURE 4.7 A high contrast value produces a high contrast image.

    You can see how, when you increase the contrast above 1, the lowlights get pushed down and the highlights are pushed up.

  13. Keep the Contrast property above 1 and bring the Center value down to 0.

    The Center property changes what is considered to be the highlight or lowlight. Colors above the Center value are considered bright and are pushed up, and colors below the Center value are considered dark and are pushed down.

    Now you can see that the result of the RolloffContrast operation is very similar to that of the Multiply node. In fact, they are virtually identical. When setting the center value at 0, you lock that value in place. The value 0 is locked in place when you’re multiplying as well.

  14. Bring the Center value up to 1.

You haven’t gone through an operation called Lift yet, but the RolloffContrast operation is virtually the same as that operation. With Lift, the value 1 is locked in place, and the further the values are away from 1, the bigger the effect. You will go through Lift when you learn about the Grade node later in this chapter.

To wrap up this part of the color introduction, here’s an overall explanation:

  • When dealing with color, usually you need to control the lowlights, midtones, and highlights separately.
  • The Add operation adds the same amount of color to every part of the dynamic range.
  • The Multiply operation multiplies the dynamic range by a value. This means that a perfect black doesn’t change, lowlights are barely touched, midtones are affected by some degree, and highlights are affected the most. It is good to mention that a Multiply operation is virtually the same as changing the exposure in a camera or increasing light. It is the most commonly used color operation.
  • The Gamma control is a specific curve designed to manipulate the part of the dynamic range between 0 and 1 (black and white, remember?), without touching 0 or 1.
  • Contrast is actually very similar to a Multiply, but has a center control. If you place the center point at 0, you get a Multiply node.
  • + Share This
  • 🔖 Save To Your Account

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