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

Home > Articles > Digital Audio, Video

Nuke 101: Color Correction

Whatever reason you have for color correcting an image, the color correction will work according to the way Nuke handles color. Nuke is a very advanced system that uses cutting-edge technology and theory to work with color. It is important to understand Nuke's approach to color to understand color correcting within Nuke.
This chapter is from the book

Wow. This is a bit naive. Calling a lesson "Color Correction." It should be a whole course on its own. But this book is about more than that, and limited space reduces color correction to a chapter. So let me start by explaining what color correction means.

Color correction is one of the most fundamental things you can do to an image. It refers to any change to the perceived color of an image. Making an image lighter, more saturated, changing the contrast, making it bluer—all of this is color correction. There are a lot of uses for color correction. The most obvious one is to make an image look different as a result of a stylistic decision. But you can also color correct to combine two images so they feel like part of the same scene. This is performed often in compositing when the foreground and the background should have colors that work well together. There are plenty more uses for changing the color of an image. An image might be a mask or an alpha channel that needs to have a different color in some way—to lose softness and give it more contrast, for example.

Whatever reason you have for color correcting an image, the color correction will work according to the way Nuke handles color. Nuke is a very advanced system that uses cutting-edge technology and theory to work with color. It is important to understand Nuke's approach to color to understand color correcting within Nuke.

Understanding Nuke's Approach to Color

Nuke is a 32-bit float linear color compositing application. A bit of a fancy description there, with potentially new words. I explain this bit by bit:

  • 32-bit: That's the amount of bits used to hold colors. Most compositing and image-manipulation programs are 8-bit, allowing for 256 variations of color per channel (resulting in what's referred to as "million of colors" when combining the three color channels). This is normally fine for displaying color, but is not good enough for some calculations of operations, and may result in unwanted results such as banding—inaccurate display of gradients where changes in color happen abruptly instead of smoothly. 32-bit allows for a whopping 4,294,967,296 variations of color per channel. That's a staggering amount that results in much more accurate display of images and calculations of operations. 8- or 16-bit images brought into Nuke will be bumped up to 32-bit, although that doesn't add any detail, it just enables better calculations from that point onwards.
  • Float: Normally the color of an image is represented between black and white. In 8-bit images, for example, the 256 color variations are split evenly between black and white—so the value 1 is black, the value 256 is white, and the value 128 is a middle gray. But what about colors that are brighter than white? Surely the whiteness in the middle of a lit light bulb is brighter than a white piece of paper? For that reason, there are colors that are brighter than white called super-whites. There are also colors that are darker than black called sub-blacks (but there isn't a real-world analogy that can be used here short of black holes). Using 8 bits to describe an image simply doesn't allow enough room to describe colors beyond black and white. These colors get clipped and are simply represented as black or white. However, in 32-bit color, there is plenty of room and these colors become representable. As mentioned before, 8-bit color is normally enough to display images on-screen. Furthermore, the computer monitor can still display only white—and nothing brighter. However it is still very important to have access to those colors beyond white, especially when color correcting. Darkening an image that has both a piece of white paper and a light bulb in it will leave the light bulb white, while darkening the paper to a gray color results in an image that mimics real-world behavior and looks good and believable. Doing the same with a non-floating image will result in the white paper and the light bulb looking the same gray color—which will be unconvincing.
  • Linear: Linear can mean lots of things. In terms of color, I mean linear color space. A computer monitor doesn't show an image as the image appears in reality, because the monitor is not a linear display device. It has a mathematical curve called gamma that it uses to display images. Different monitors can have different curves, but most often they have a gamma curve called sRGB. Because the monitor is not showing the image as it appears in reality, images need to be "corrected" for this. This is usually done automatically because most image capture devices are applying an sRGB curve too, in the opposite direction. Displaying a middle gray pixel on a monitor only shows you middle gray as it's being affected by the gamma curve. Because your scanner, camera, and image processing applications all know this, they color correct by applying the reverse gamma curve on this gray pixel that negates the monitor's effect. This process represents basic color management. However, if your image's middle gray value isn't middle gray because a gamma curve has been applied to it, it will react differently to color correction and might produce odd results. Most applications work in this way, and most people dealing with color have become accustomed to this. This is primarily because computer graphics is a relatively new industry that relies on computers that, until recently, were very slow. The correct way to manipulate imagery—in whatever way—is before the gamma curve has been applied to an image. The correct way is to take a linear image, color correct it, composite it, transform it, and then apply a reverse gamma curve to the image to view it correctly (as the monitor is applying gamma correction as well and negating the correction you just applied). Luckily, this is how Nuke works by default.

Still confused? Here's a recap: Nuke creates very accurate representations of color and can store colors that are brighter than white and darker than black. It also calculates all the compositing operations in linear color space, resulting in more realistic and more mathematically correct results.

Nuke has many color correction nodes, but they are all built out of basic mathematical building blocks, which are the same in every software application. The next section looks at those building blocks.

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