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Chapter 4. 2-D Animation > Pencil Test or Line Test

Pencil Test or Line Test

In traditional cel animation, after all the pencil drawings are made, they are filmed one at a time under a movie camera onto film, and the animators watch this film, called a pencil test or line test, played at full speed, to test the motion and check for problems in the animation.

Pencil tests are greatly simplified by using a computer, but how you do it depends on your original artwork and on the hardware and software that you have available. Assuming that you scanned all your images, importing them into an animation program for a pencil test is usually child's play and can be done very quickly. When the images are imported, they are simply saved as a QuickTime or AVI movie and played back at full speed on the computer. This saves the time and expense of filming and processing the film.

The work that goes into scanning the images into the computer is not a dead end, as it is with filmed pencil tests. If you are using a cel animation program that supports it, you can go directly from the pencil test to inking and painting the cells. Alternatively, if you're using a paint program, you can open and paint the scanned images there. Or if you're using a vector animation program, such as Flash, you can perform an autotrace on the scanned drawings to bring them into the program's vector artwork.

There are several ways to scan hand-drawn animation images into the computer. The most common input devices are flatbed scanners, video cameras, and digital cameras.

Scanner

Flatbed scanners are very inexpensive and easy to operate, and you can easily set one up so that it's always ready to scan animation. An appropriate scanner for Web animation is a standard-size (8.5 × 14 inch) grayscale flatbed with a minimum resolution of 300 dpi. Early in 1998, scanners that fit this description were selling for about $100.

Assuming that you're creating your drawings on an animation disk or a drawing board with a peg bar attached, the first thing that you'll need to do is to tape a peg bar to the edge of the scanner bed, using Mylar or other nonstretch tape. (Don't use masking tape, electrical tape, or gray duct tape, all of which stretch, allowing the peg bar to move and causing scans to lose registration from one to the next.) When you're completely comfortable with the positioning of the peg bar, you may want to glue it into place with epoxy, but keep in mind that peg bars and scanners sometimes break, so you may want the option of removing it later.

After you've drawn your animation cels, you simply transfer them to the scanner, place them on the pegs one by one, and scan each subsequent image with the same scanner cropping settings. To make sure that the settings are the same from scan to scan, save the scanner settings to a file. If the scanner won't save the scanner's crop settings, make sure that you scan the full size of the scan bed; then create a macro or an automated cropping routine in your paint program to make sure that every scan is cropped exactly the same way. This practice prevents registration errors between frames.

Figure 4.12 shows a flatbed scanner with a taped-on peg bar that matches the one on my animation disk. Taping the peg bar perfectly straight on the scanner helps eliminate the tedious and registration-threatening step of rotating each frame after you scan it, although with this setup, my Photoshop Action (script) for batch-processing scanned images includes a 90-degree rotation, because the image is initially scanned on its side.

Figure 4.12. Flatbed scanner with taped-on peg bar.


Scanning in this way can get pretty tedious, particularly if you have a slow scanner. To solve the problem, Linker Systems' Scan Link software automatically locates registration pin holes on standard animation cels and uses them to register frames of animation in software. This allows you to stack many frames of animation on a scanner's sheet feeder and set them to scan overnight. Keep in mind, however, that 12-field animation paper is slightly larger than the scanning bed of a standard legal-size scanner, and 16-field paper is much larger, so you'll need a large-format (11 × 17) scanner to take advantage of this feature. Fortunately, the price of such scanners is coming down fast, although the availability of sheet feeders for these scanners is very limited.

Tips for Scanning Animation Drawings

Tip

Check the scanner for mechanical consistency. Try scanning the same drawing several times without moving it and importing the images into an animation file. If the scanner's positioning is consistent from frame to frame, the drawing will appear perfectly still on-screen. If, however, the drawing jitters or jumps from frame to frame, this problem indicates that the scanner's head position varies from frame to frame, which will cause your animations to vibrate.


Tip

Scan your images at 1.5 to 2 times the final resolution of your animation. If your drawings are 8 × 6 inches, for example, and your final animation will be 640 × 480 pixels, you'll need to scan your drawings at 120 or 160 dpi (160 × 8 = 1,280, which is twice the horizontal resolution of the final animation). If you scan your drawings too small and have to scale them up, you'll end up with jagged lines in your final animation. Also, scanning and working with animation images at high resolution and then scaling them down for the final animation allows you to touch up small details much more easily than if you start with the drawings at low resolution. Keep this in mind if you're planning to use a video camera or low-end digital camera for grabbing images. These cameras' maximum resolution is typically 640 × 480 pixels, which is exactly the resolution of most 14-inch monitors, which leaves no room for error or for scaling up any part of a drawing, if you're planning to do full-screen animation.


Tip

When you've determined a correct scan setting, which typically includes brightness/contrast and cropping position and dimensions, save the scanner's settings. This way, if you have to continue a session later (which is likely), you'll be able to load the scan settings, and the new scans will look just like the old ones.


Tip

Use manual scan settings. Many scanner drivers include automatic exposure correction, which is usually not tuned for animation drawings. In addition, autoexposure values will likely change from frame to frame, meaning that some frames will be exposed differently than others, which may cause disturbing variations in the weight of lines from drawing to drawing.


Tip

Create a script in your image-editing program for scanning, rotating, adjusting values, and cropping your scans. (Scripts are called Actions in Photoshop, and they are sometimes called macros in other software.) This serves a double function: It speeds your work, by letting you perform multiple operations in a single step, and it also prevents unintentional errors, such as rotating or cropping one or more frames with different values, which can be almost impossible to correct later. (I use DeBabelizer, which handles not only batch scanning, but also batch image adjustment, cropping, and fine-tuning.)


Tip

Macro applications, such as QuickKeys (for the Mac) and Keyboard Express 95 (for Windows), let you create macro functions for many applications, such as scanner software, whether or not the software has built-in scripting functions.


Tip

Name sequential files with leading zeroes. GIFBuilder, DeBabelizer, and many other animation utilities automatically import files that are properly sequentially numbered. A1.GIF, A11.GIF, and A101.GIF will not import in numerical order; A101 comes before A11, alphabetically speaking. A001.GIF, A011.GIF, and A101.GIF, however, import in the proper numerical order. The rule is to add enough leading zeroes so that all the numbers in the sequence have the same number of digits—for example, 0002, 0020, 0200, and 2000.


Eye Cam

Another low-cost way to scan animation frames is to use an "eyeball" camera, such as the ones from Connectix. These cameras allow you to grab frames directly into your painting or animation software by using a plug-in or a TWAIN driver, and you can mount them on a standard camera copy stand (see "Digital camera" later in this chapter). The older grayscale cameras have fairly low resolution (320 × 240), and their image quality isn't spectacular, but it's adequate for the needs of many Web animators. The newer color models have 640 × 480 resolution and are more versatile.

One of the problems with these cameras is that their cheap lenses cause vignetting at the corners of an image. The ANIMAC software comes with an anti-vignetting filter that you can attach to solve this problem, or you can construct your own (see Chapter 5 for more on ANIMAC).

Digital Camera

Like low-cost video cameras, digital still-frame cameras have become very affordable, and the resolutions of most of these cameras are adequate for most Web animation purposes. Generally, the quality is much better than what you'll get from a cheap eyeball video camera. Most digital cameras do not suffer from the vignetting that is common in video cameras. You can mount a digital camera on a standard camera copy stand (see Figure 4.13) and use it to grab frames directly into your animation program.

A copy stand is simply a table that has a bracket to hold the camera in position above the subject. Typically, the table has two or more lights mounted at approximately 45-degree angles to the work, providing even illumination without glare or shadows.

Before purchasing a digital camera for animation, check with the manufacturer to make sure that the camera can be controlled directly by the image software, through a TWAIN driver

Figure 4.13. Typical camera-stand setup, showing a digital camera attached.


or Photoshop plug-in, for example. This lets you snap the pictures of the frames directly from within your animation or drawing software. The alternative is to transfer the images from your camera to your computer after you've shot as many as the camera will store, which is inconvenient.

You can capture images from a digital camera or eyeball camera in many different ways, depending on your software and hardware setup. In Photoshop, for example, you can use an acquire plug-in (if one is available for your camera) that snaps the image. Furthermore, you can create a script, called an action, which automatically grabs a new frame from the camera and exports it as an image file. These image files in turn can be imported into GIF Builder or GIF Animator, for example, and combined into a single animation.

Equilibrium's DeBabelizer excels at scripted image capture and processing, with the advantage that scanned images can automatically be optimized and appended to an animation file.

If you have drawn your images directly into a software program, you avoid the scanning step altogether. You can simply import the finished images into an animation program and save them in the appropriate animation format.

Black and White or Grayscale?

When you are scanning pencil drawings, regardless of the scanning device, you can scan the lines in two ways: as pure black-and-white aliased lines or as antialiased grayscale lines. Both styles have advantages (see Figure 4.14a).

Black-and-white lines compress very well, so they download and play back quickly. They also are easy to fill with color, because most programs pour color into every white pixel, right up to the edge of the lines. The downside of black-and-white lines is that they appear very hard-edged and "jaggy," particularly when viewed up close or magnified.

Antialiased lines use shades of gray to blend lines into their surrounding colors. The advantage is that antialiased lines appear to be very smooth and slightly soft on the edges, more like natural ink on paper. The disadvantages are many. The first is that most paint programs recognize the shades of gray along the edges of the line as being nonwhite and do not fill these areas with color when it comes time to color your animation's cels. This results in regions of color bordered by a thin line of white surrounded by black, which is almost never desirable. See Figures 4.15b and 4.15c.

Most animation and paint programs, such as Photoshop and Painter, let you blend color fills into the gray border regions with a paint-bucket tolerance setting that determines the number of gray levels to interpret as white. This results in smooth color fills without the white edges.

The final pitfall of grayscale (antialiased) lines is that they don't compress nearly as well as flat regions of solid color, so they take longer to download.

Figure 4.14a. Antialiased lines have soft gray edges that make lines appear smooth. Aliased lines have jaggy edges, but they minimize other problems.


Figure 4.15b. Antialiased lines can result in unwanted edge borders between color fills and lines.


Figure 4.15c. The final pitfall of grayscale (antialiased) lines is that they don't compress nearly as well as flat regions of solid color, so they take longer to downfload.



Viewing the Pencil Test

In almost any animation or desktop video-editing program, you can compile your animation's frames and save the movie to play back at the normal frame rate directly on-screen—typically, as a QuickTime movie, animated GIF, or Flash file. Normally, you'll also be able to combine the movie with the audio track, if any, and preview the results. This reveals whether the animation's timing, motion, and sound synchronization work out. If they don't, you can sometimes adjust the timing by adding twos—duplicating a frame to slow things down—or deleting a frame where action is too slow. If you're creating a GIF file, you can adjust the timing of individual frames by setting their delay values. If these methods don't correct the problem, you may need to go back to the drawing board to add, delete, or change frames.

Unless you are using a dedicated cel animation system, such as X Sheet, Retas, or Animation Stand, it is very likely that you'll have to back out of your animation program when the pencil test is complete. The next step—inking and coloring—typically has to be done in a painting program; then the colored frames are reimported into your animation program to composite the final, finished animation.

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