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Shoot Review — Red Giant Primatte Keyer 3.0 for After Effects

Image A. Here''s the original DV greenscreen footage with the arjpgacts clearly apparent along the black edge of the jacket.

Nowadays, compositors have several good chroma key products to choose from, including Primatte, the Foundry's Keylight, dvGarage dvMatte Pro, Digital Film Tools zMatte, and, of course, Ultimatte AdvantEdge. All these products will pull very clean keys from film footage, but digital video such as MiniDV and HDV is another matter. Primatte Keyer 3.0 from Red Giant Software, the latest version of this popular keyer, has been rewritten to handle video footage. Lots of other new features make it easier to key and clean up mattes and foreground elements.

Image B. The result of turning on Primatte''s de-artifacting. Hit a button and it''s gone.

All keying, whether based on chrominance or luminance, uses algorithms that distinguish between foreground and background elements. The better the bit depth of the source, the better the key. That's because the background color or key color should be as narrow a portion of the spectrum as possible. That way, when the software removes the key color, it has the least possible effect on the foreground. The trouble with DV and HDV is that the sampling rate is low on the color channels, which introduces blocky artifacts.

Popular formats like MiniDV, DVCAM, and DVCPRO sample NTSC at 4:1:1. In YUV color space, this means that the luminance channel is sampled at four times the rate of the two color difference channels. This works for basic imaging — human visual perception of detail relies more on differences in luminance than color, so this produces good apparent detail while keeping data rates low. Chroma keying, on the other hand, is based on color, so these lower sampling rates are a problem. The edges in Image A exhibit typical DV artifacts that are caused by the low sampling rates in the color channels.

Before developers addressed DV artifacts in various keying programs, artists discovered a few tricks to knock out the artifacts in DV. They'd redigitize footage with an analog connection or just slightly blur one of the color channels. Both solutions tended to soften the blockiness, which improves the quality of matte edges, but this requires experimentation and an extra pass on the footage.

Internally, Primatte 3.0 is doing much the same thing when users select one of four options: None, DV/HDV, DVCPRO, or Other. There is also a Strength slider measured as a percentage (0 to 100 percent). The results of Primatte's de-artifacting (at 100 percent) are shown in Image B. I compared Primatte's results to those of Keylight and Digital Film Tools zMatte and found the de-artifacting in Primatte to be the cleanest without additional tweaking. The initial de-artifacting results in Primatte are very, very good.

You''ll see four panels under the Keying option. You work from left to right. When you''re done, the basic key is clean and ready for spill removal.

Workflow


I have used many keyers, and Primatte has one of the most intuitive and straightforward workflows. Using this as a plug-in for After Effects, you begin a project by selecting Primatte from the Effects menu, which brings up the familiar gray parameter panel. If you are working with digital video, you can apply de-artifacting at any time, and it processes in a couple of seconds.

The main work of keying takes place under the Keying option. Twirl down the arrow and you will see four buttons for Select BG, Clean BG, Clean FG, and Fine Tuning. Select BG turns the Arrow cursor into a sampling tool. You can point-click the background per pixel, or you can draw a line that leaves a trail of sampled pixels. Primatte averages the multiple samples. Within a second, the key color disappears and you have 90 percent of your keying done. New in Primatte 3.0 is a rectangular selection option that draws a marquis around selected pixels. For unevenly lit backgrounds, this is faster than making multiple point samples.

Also under the Keying area are View options: Comp, Matte, Foreground, Background. The default is Comp, but you would now select Matte for the next step: Clean BG. Matte view displays the alpha channel. There will most certainly be gray areas that you will want to remove — a perfect result is to have only white in the foreground and black in the background. Gray is only appropriate on transparent objects such as water or smoke. You clean unwanted gray pixels by making additional samples of these imperfections with the same sampling tool. One thing you don't sample at this time are the transition areas between the foreground and the background. Edge cleanup is done separately.

Once this is completed you move on to the third area in Keying, Clean FG. Here you repeat the process of selecting gray areas that are not edges — but this time only in the foreground of your footage. When you're finished cleaning the FG, your key should be looking fairly good. However, there will almost certainly be color contamination caused by light spill from the background on the edges of the foreground subject.

You have two options at this point: use the Correction tools or use the new Fine Tuning feature. Actually, Fine Tuning is a parameterized version of the Correction tools that were always in Primatte. Fine Tuning was added because the Correction tools are applied without calibration. Fine Tuning lets you adjust the Spill, Transparency, and Detail with sliders. A very slight adjustment makes a very big difference with these sliders, so don't go overboard.

The original spill cleanup option involved using the Spill Sponge, Matte Sponge, Restore Detail, and Decrease Opacity. These involve selecting problem areas with the sampling tool in a more intuitive and graphic way than the Fine Tuning tools allow. However, because Primatte is fast and updates quickly, Fine Tuning allows for good interactivity. Either way, a few samples and the spill begins to disappear. This usually does the trick, but later you have one additional operation that can reduce spill.

Another simple but important new feature is the ability to keyframe the primary background key color selection. This is useful for situations in which the lighting at the greenscreen shoot changes — for example, a cop car's flashing lights affect the background. In this case, the initial samples would be made throughout the footage at the peak of any change.

Primatte has several edge refinement tools such as Defocus Matte, Inward Defocus, Shrink Matte, Edge Color Replace, and Replacement Color. In the past, these processes were applied using other filters available in After Effects. The trend in the latest version of most keying products is to add these tools to the keyer. This makes sense, and Primatte 3.0 has provided one of the most complete sets of these additional cleanup tools.

This is apparent in two new tool sets in version 3.0: Alpha Controls and Composite Controls. In addition to adding Gamma control, the Alpha Cleaner section has six tools for eliminating specks and holes in the alpha channel. These new percentage sliders allow global cleaning of the matte without having to sample every speck. It's great to have all these tools under one roof and within an orderly workflow.

This is the correction workflow. The operations here can be duplicated within Keying—the Fine Tuning option allows for correction using parameter sliders.

After the key


In addition to the Alpha cleaner, the new Composite Controls include three tools that are usually applied to the subject footage and don't really affect the key itself. These new tools are Spill Killer, Color Matcher, and Light Wrap. Spill Killer allows sampling of contaminated areas that are then replaced with the opposite color of the key once you select Red, Green, or Blue. The spill effect is refined with sliders for Range, Tolerance, and Strength.

Color Matcher is similar to the new Photoshop CS2 filter used for matching elements in a comp. This is necessary because it's hard to match the ambient light in the background plate when shooting a subject in front of a greenscreen. Color Matcher makes the determination of the overall cast of the background and applies it to the foreground. This is nice to have in the keyer workflow, and it works fairly well. However, After Effects' other color correction tools offer more sophisticated ways to match color. Primatte's Color Matcher does a good job and may be sufficient in many situations. It's there if you need it.

The last of the Composite Controls is Light Wrap, which is, again, a staple of third-party image enhancement tools sold separately from the keyer. Primatte's light wrap is quick and easy to use.

If you want more refinement than this tool provides, After Effects has many, many additional color edge and color correction filters. This is not to say that Primatte's Light Wrap will be insufficient for most of your work, but in serious visual effects work, comp artists usually find their own sets of tricks to properly integrate elements into a shot. The fact is that most integration problems in a key are due to improper lighting of the subject. Frankly, matching studio lighting to the sun is rarely done well and is very difficult to fix later on. This is a very common problem in visual effects work.

Conclusion


Upgrading or purchasing Primatte 3.0 is easily justified if you are going to be doing keying of video footage, or if you're relatively new to keying and don't have a workflow and third-party cleanup filters. Apart from the addition of the video de-artifacting tools, Primatte 3.0 has added all the essential compositing and matte cleanup tools and made them part of a straightforward workflow. For the relatively low cost of the software and the time saved from not having to open lots of other filters, Primatte is a complete keying solution. More often than not, this is the first keying tool I open, mainly because of the simple workflow and fast, high-quality results. Highly recommended.

Special Thanks to Alex Lindsay of dvGarage for the sample greenscreen footage. You can find excellent keying and VFX tutorials at
www.dvgarage.com.


Bottomline


Company: Red Giant Software
Fort Wayne, Ind.; (260) 625-5343
www.redgiantsoftware.com

Product: Primatte Keyer 3.0 for AE

Assets: Straightforward workflow, high-quality output, has all the necessary tools to pull a clean key.

Caveats: In Fine Tuning, very slight adjustments make a big difference.

Demographic: After Effects users keying HDV and DV footage.

PRICE: $695