Inside Combustion 2
Page 3 of 4
I found the paint and roto tools extremely responsive, given the RAM cache management system that Combustion is using. It is so important to be able to see the results of your paint and roto in realtime. And the ability to do this without having to make a preview each time you need to view it is invaluable for production. Not only do you get the immediate feedback that you need for this, but if you have a post house with combustion licenses and a flame or inferno, the roto/paint work can be done on the lower end machines, and then the data can be transferred over to the high-end systems for final composite. This, in fact, is applicable to all the parameters in Combustion – color correction, keying, spline data, etc. can all be ported over to the SGI’s and vice versa. [an error occurred while processing this directive]
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| Combustion's Roto Tools window |
Painting with vectors allows you a great deal of control, but when each stroke contributes to more calculation time, the composite can get very heavy very quickly. To alleviate this, Combustion provides a process where you can commit an operator to disk. When you commit, Combustion will render the flow up to the operator that you chose to commit – in this case it would be the paint operator. It will then create another node in your composite that brings in the committed footage and it will create a switcher operator that enables you to toggle between the committed footage and the actual flow. This speeds up the rendering process tremendously by removing the heavy paint calculations, but it gives you the freedom to switch back to the original flow and make changes if necessary.
Discreet purchased Illusion, a 2D particle generator, last year, and incorporated it into the Combustion pipeline. The system is deep and robust and quite complex. The amount of control the artist has seems bottomless. However, discreet has provided a substantial library of particle presets that will keep any artist happy and busy with systems ranging from fire to smoke to explosions to water to flowers. Nearly every parameter is animatable and has a learning curve of its own beyond Combustion itself. The particles not only can use points, but also image-based sprites. You can even take the output of a particular operator in the Combustion flow and assign it as a particle. The emitters and deflectors within the system can be animated and can also be attached to a tracker. So, you can track a position on the live action footage, like a cigarette tip, for example, and then have a particle emitter attached to that track point, giving the impression that the cigarette is burning.
Despite the capabilities of the particle system, I would really like to see controls to influence the systems with forces like wind, gravity, turbulence, etc. Having control over killing particles and spawning would also bring this feature to a state that could more effectively replace a 3D particle system.
The discreet keyer is a port from FFI in the SGI world. The same tools that the larger houses use are available in this relatively low priced package. All the tools within the keyer are designed to finesse a matte into place. Other keying systems such as Primatte, Ultimatte, and UltraKeyer (Digital Fusion), are geared toward getting the matte quickly and effectively. And as effective as they are, the finessing tools for controlling the edge, suppressing spill, and the density of the matte don’t seem to be as broad as the discreet keyer. The keyer allows for multiple methods of pulling the key including RGB, YUV, HLS, RGBCMYL, Luminance, or any pure color channel. Each method is stored as a different key, so you can compare the quality of each matte pull. Beyond that you not only have the ability to choke, expand, and blur the matte, but you can erode the edges which changes the transparency of the edges without actually removing pixel information. Softness of the matte can be controlled globally as well as individually for each color channel.
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| Combustion's Key Tools |
Combustion also carries a feature that I have not seen in other compositing programs, and that is the idea of controlling both a front and a back matte. These terms are equivalent to the matte and the holdout matte in optical compositing terms. In digital compositing, you generally have the one matte that is assigned to the foreground object. In optical compositing, you not only need the matte for the foreground object, but you need another matte to create a hole in the background to prevent a double exposure. The two mattes are equal in shape and inverted in value. Combustion gives you curves to control how the edges of the mattes change from white to black. Finessing these values creates a difference between the two mattes, blending with one another along the edges. This creates a polluting of one image into the other, creating a more seamless compositing.
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| Click image to see larger view of Combustion's Curves function |
Spill suppression is given a set of curves as well. You can have the control of desaturating a particular area of color, or adding the compliment that the spill color into the image (magenta is usually added to green spill, for example). You are also given the ability to choose a color that will replace the spill color. This is helpful if your subject is in front of a particular color, like a sunset. You can take the oranges of the sunset and assign them to the spill color, again, making the composite more seamless.
The Color Correction tools for Combustion are just as wide, if not wider than the keying tools. Again, coming from the FFI, these tools have gone through many years of development and have developed because of project upon project needing solutions to problems. The tools provided give you access to each color channel individually, but you can also adjust color based on tonality, general hue, and tint. You can control with a color wheel, or curves and a histogram. On top of just adjusting the values of colors, you can make a comparison between clips (a foreground and background, for instance), and match the color between the two to provide for a more integrated composite.
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| Click image for larger view |
Within these color correction tools is the capability to correct within a number of different bit depths – 8-, 10- 16-, and floating. When working with files that are a higher bit depth, the color corrector has a lot more range to work with and will give you more accurate results if you need to shoot out to film. You also have less to worry about when it comes to colorbanding or clamping when values begin to go out of range. This multi-bit depth capability does have a downside however, which is not a limitation in Combustion, but rather a limitation of the computer monitor in general. This is trying to work with files that contain more colors than the display can provide.
Combustion is able to now import and export color Look Up Tables (LUT). This is nothing new to programs such as Digital Fusion and Shake, but Combustion lacked this in its previous iteration. LUTs refer to how a program will assign out of range color values to colors that can be displayed on a monitor. This is based on a curve function, which can be displayed in Combustion to control the values in order to have the display on you monitor to best reflect what will ultimately be put onto film. Combustion also provides a setup of test patterns to calibrate the monitor you are working with.
Another quality of film, is that it has grain – something that CG images do not have by default. Combustion provides numerous grain management tools to not only add grain to CG imagery, but also remove grain from footage for things like creating cleaner bluescreens. For adding grain, you can actually choose from a number of preset film stocks. Or, you can analyze the grain of a piece of footage so that Combustion can recreate that grain structure. I am generally impressed with the ability to sample grain and match, but the algorithm for removing grain, which is essentially made of a noise filter and a soften isn’t really as effective as sampling and averaging the grain over a series of frames.
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