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

Home > Articles

This chapter is from the book

Track Mattes

Track mattes are the primary method by which you can use the alpha or luminance information of one layer to set the transparency of another layer ( Figure 3.37 ). This is actually the normal way to apply a matte channel in many compositing applications, which don't have the concept of the alpha channel so firmly integrated into the overall pipeline as After Effects.

03fig37.jpg

Figure 3.37 A basic alpha track matte setup: The alpha of layer 1 is set as the alpha of layer 2 via the highlighted pull-down menu. The small icons just to the left of the layer names help remind you that this relationship has been set up, and which is the color layer and which is the matte.

The perceptual difference between an alpha channel and a track matte isn't, for the most part, too difficult to grasp. In both cases, you have pixels with a value (in 8-bit color space) between 0 and 255, whether they are color or grayscale alpha pixels. That any image would be interchangeable with the alpha channel shouldn't be too shocking; even if you're using the luminance of a full-color image, After Effects simply averages the 0 to 255 value of the three color channels into one value. The principle doesn't even change in 16-bit color—it's just the same range of values, with finer increments, being sampled.

You set a track matte by placing the layer that contains the transparency data directly above its target layer in the timeline and choosing one of the four options from the Track Matte pull-down menu:

  • Alpha Matte: Uses the alpha channel of the track matte layer as if it were the alpha of the underlying target layer
  • Alpha Inverted Matte: Does the same as Alpha Matte but inverts the result, so that the lighter areas of the alpha are transparent and the darker areas are opaque
  • Luma Matte: Uses the luminance data of the track matte layer (the relative brightness of the red, green, and blue channels combined) as if it were the alpha of the underlying target layer
  • Luma Inverted Matte: Does the same as Luma Matte but inverts the result, so that the lighter areas of the alpha are transparent and the darker areas are opaque

By default, the source layer for the track matte (the upper of the two) has its visibility turned off when you set the track matte, which is almost always what you want. This sets the track matte with a single click to the Track Matte pull-down menu. If you need to adjust the source after setting it, you can always temporarily turn it back on; just remember to turn it back off when you're finished.

Why They're Useful

Track mattes are not the only way to apply alpha or luminance data to the transparency of a layer, but they're the clearest and most straightforward way. They help you out of a lot of jams in which creating a selection via other means would be inconvenient or in which mask or matte features constrain you.

For example, it's not possible to track a mask in After Effects. But it is possible to apply the mask to a track matte instead, and then to track that layer (instead of the mask itself). Chapter 8, "Effective Motion Tracking," discusses this in detail.

In Chapter 6 you will learn of the many ways to pull a key, including hi-con mattes. Some of these methods apply their results directly to the alpha channel of the target layer, but others cannot. Additionally, specific operations such as blue-screen keying can change the color of the source (automatically removing blue spill from the foreground); applying the key via a track matte to a duplicate clean source instead is an effective workaround if you want the matte but not the despill.

Why They're Occasionally Tricky

Unlike with parented layers (described in Chapter 2, "The Timeline"), selecting a track matte layer does not lock it to the current layer. In fact, setting a track matte means that no matter which layer is next higher in the stack, that layer is the source of the matte. Thus, accidentally moving a layer in between a layer and its track matte can cause easily solvable but, nonetheless, disastrous results.

When you duplicate a layer with a track matte activated (Ctrl+D/Cmd+D), After Effects automatically duplicates it above the matte layer or two layers above the current layer. If you duplicate the matte layer at the same time, the duplicate will also move up two layers, so that all layers preserve their proper track mattes ( Figure 3.38 ). That's good. What's bad is if you forget to duplicate both layers, because the track matte remains active in the duplicate layer, even if it has been duplicated to the top of the stack, and you can't see that it's active.

03fig38.jpg

Figure 3.38 Selecting and duplicating the layers from Figure 3.37 creates two new layers that leapfrog above the previous layers to maintain the proper color/matte relationship in the source and duplicate layers.

If the layer to which the track matte is applied already has an alpha channel, then the new selection area created by the track matte will be opaque only in the areas that are opaque in both mattes. So applying a track matte in this situation is like making a subselection of the current selection.

Render Order

Also tricky to work out with track mattes is the render order: Sometimes adjustments and effects that you apply to the matte layer are applied to the target matte, and sometimes you must first pre-compose to get the applied effects and adjustments.

And what happens if you apply a track matte to a track matte? It's actually hard to say; sometimes it will work, sometimes not. The user interface does not prohibit this behavior so you can try it, but a better idea is probably to pre-compose the first instance of track matting and apply the second track matte to that nested composition.

The next chapter, "Optimizing the Pipeline," looks in depth at solving issues related to render order, and you'll begin to use After Effects as a visual problem-solving tool for these issues.

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