|Nuke: Project managment||Florian||2004-07-15|
|Nuke: Launch Framecycler without loading frames||Sean Looper||2004-06-16|
|Nuke: Script Drag n' Drop||Wonko||2004-01-28|
|Nuke: 'Sliding' Numeric Input Fields||Wonko||2004-01-28|
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|Day Sky: Latitude and Longitude Coordinates||Matt Leonard||2007-02-19|
|Simulating liquid reflections with Digital Fusion 4.02||Chris Maynard||2003-07-27|
|DF: cloud/vapor displacement||Chris Maynard||2003-07-02|
|Fluid simulation with displacements and grid warp||Chris Maynard||2003-06-10|
|microthermal turbulence in fusion 4||Chris Maynard||2003-06-05|
|Digital Fusion: Color Matching||Jason Kolodziejczak||2003-01-29|
|Digital Fusion: Using the new Grid Warp tool||Jason Kolodziejczak||2002-11-25|
|Digital Fusion: Type On Text||Jason Kolodziejczak||2002-09-14|
|Digital Fusion: Color Suppression||Jason Kolodziejczak||2002-09-14|
|Digital Fusion: Creating Fireworks||Jason Kolodziejczak||2002-08-31|
|Digital Fusion: Pulling an Ultrakey||Jason Kolodziejczak||2002-08-31|
|Digital Fusion: Tracking Tips||Mike Seymour and Jason Kolodziejczak|
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|Free Video tutorials for Smoke and Fire 7||Alan Souza||2005-07-27|
|Creating Borders on Text in the DVE||Brian Mulligan||2005-07-09|
|Using Excel as an Animation Tool for smoke/fire||CE Raum||2005-05-16|
|Creating a selects reel for Tape-to-Tape after the conform||tim farrell||2005-03-20|
|3/2 pulldown in 720P projects||tim farrell||2005-02-01|
|How to Make a Line Wipe Transition||Mark Longchamps||2004-11-04|
|The dAMer||CE Raum||2004-09-08|
|Smoke Shortcuts||Brian Fox||2004-03-11|
|fire: Easy End Credits With Single Frame Image Files||Jesse Morrow||2004-03-05|
|3 Basic Uses of Layer Re-Entry in Fire/Smoke||Tim Farrell||2003-10-17|
|Fire/Smoke - Combining Mattes in DVE||Tim Farrell||2003-09-30|
|Fire Tiling Helper||Jef Huey||2003-01-28|
|Using 3D geom to import and zoom||karen m boyle||2002-08-02|
|fire - Control Multiple Surfaces/Axes||Scott Ellman|
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Several tracking tips to keep in mind the next time you supervise on set.
Tip Number 1 - Try Using Yellow Markers on Green
On green screen - use yellow markers and separate the components separately for tracking and keying. On the left, you can see what the full color rgb image looks like. Note that if you use the green channel only (middle image), the markers are easily keyed and you avoid time consuming marker removal. The red channel provides a great high contrast image for tracking.
Tip Number 2 - Use Newspaper as Pattern for 3D Tracks
Newspaper makes an excellent tracking pattern for 3D trackers. If you have a large green screen set, lay down newspaper away from the keying area and the non repeating - highly detailed patterns of the news paper will track really well.
Tip Number 3 - Marker Placement for 3D Tracks
If you are filming a greenscreen, it is important to not just have markers on the same flat greenscreen background, markers need to be at different distances from the camera for a good 3D solution.
Tip Number 4 - Round Adhesive Labels
Good premade tracking marks are as close as your nearest Office Depot or other office supply store. Avery makes a variety of colored dot stickers in a variety of sizes. Their web site shows a large variety of sizes and colors and don't take up much room in your travel bag.
Tip Number 5 - Keep the Greenscreen in Focus When it Makes Sense
For compositors, this is a pretty obvious tip. Sure, there are times when this isn't a steadfast rule and the lens choice requires a soft-focus background. But we mention it here because you might be surprised how many times this isn't simply basic procedure on set. It never hurts to mention it on a technical call, especially if you're not going to be on set for the supervision. The first time you get back some footage with all the tracking marks way out of focus and you don't need it that way, you'll remember to mention this
Tip Number 6 - Special Case - TV and monitor screens
One area that people tend to "over mark" is when shooting TV and monitor screens. Often the best comp can be done by shooting with the unit just turned off instead of covering the tube with blue or green screen. This let's you get realistic reflections that you can kiss back in to make the comp better. You can usually pull tracks off of the corners easily or off some detail in the case. If tracking marks are put on the face of the screen, and you are trying to keep the reflections, removing the marks can be tedious.
Obviously you will have to use some judgement on each shot. If someone with frizzy hair is going to linger in front of the monitor you may prefer to cover the face with blue or green material and add tracking marks. This will result in you not getting any real reflections, but general reflections can be faked easily.
One thing you DON'T want to do is let them feed a color generator to the monitor - "look it's blue" ... this is a frequent production thought and one that rarely works well, if at all.
Also check carefully thru the viewfinder for what is actually being reflected to make sure it is what you want and is not the camera, some lights and a crew member. Reflections can be hard to see on video assist.
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Matching lighting which is part of a photographed background is a staple art of Technical Directors and FX artists. It is an art more than a science. Below Andrew Whitehurst (see: Charile & the Choc. Factory fxg podcast) presents some basic thinking and principles to tackle such an assignment. This technique uses no raytracing, no Global Illumination and no HDRI. This is because in real-world production it can be prohibitively time consuming to render using these more advanced techniques. The majority of FX shots you see in film are produced using nothing more sophisticated than depth-map shadows and reflection and environment maps.
The majority of FX shots you see in film are produced using nothing more sophisticated than depth-map shadows and reflection and environment maps.
OK, so how do we tackle this problem? Well the first thing to do is have a good look at your background plate. For this shot I had been asked to add an CG aircraft taking off to a photographed backplate. I had been given no reference images and no tracking data. I duplicated the shot's camera move by hand in Maya and I animated the aircraft to the CG camera move. Once this was done It was time to look at the plate and extract the information I would need to light the CG elements in the shot.
Film and video seldom represent true black in their images. In this plate the circled area is scene black i.e. it is in total shadow. However, looking at the pixel values shows that the average shadowed pixel is roughly R=30, G=29, B=32. Therefore I should not let any element of my CG lighting become darker than that, as it will stand out when it is composited. To achieve this I add an ambient light to the scene.
Here is a render showing the ambient light's contribution to the scene. This is as dark as the CG elements will get. This was achieved with one ambient light tinted to match the slightly blueish cast of the shadows in the background plate.
As I had been given no reference for this scene it was necessary to estimate the light direction from objects present in the photographed plate. This water fountain's shadows gave a good indication of the angle and intensity of the key light and I was able to set my CG light to match this angle.
This area of wall which is actually only just off-white indicates that the key light should be an orange/pinkish colour. It is always a good idea to find an object in direct light in your backplate which is close to white as this will give you your cue as to what colouration should be given to the keylight.
The Keylight Pass
Here is the render of the key light's contribution to the scene. Its intensity, direction and colour are all derived from looking at the background plate. Now all that's left to do is add the fill light to the scene.
The Fill Light Pass
Adding the fill lights is a bit of a black art. There is no rule of thumb on this other than that they are generally a similar colour to the ground or walls in a scene (they represent bounced light after all) and that generally they are placed in the opposite direction to the key light. Using the backplate as reference, keep adding fill light till the ratio between light and shade looks similar to the photographic backdrop.
Once all ambient, key and fill light passes are combined they look like this. All that now remains is to composite these elements with the background plate and to add any effects passes, like particles for example, to complete the shot.
The Finished Shot
By adding some noise to the CG elements, blurring their edges and tweaking the values of the colour balance and contrast etc. the final composite can be produced. Rendering all the passes as separate elements gives your more control over your final image in comp. By this I mean you can increase or decrease the amount of key or fill by tweaking the individual layers rather than having to render the whole sequence again from scratch. This sequence also has a particle pass rendered from the exhausts which was also used as a matte to add some heat haze to the background plate.
This is not an exhaustive guide to matching real lighting by any stretch of the imagination but I hope it gives you some methods and strategies for tackling this complex problem. This was a pretty simple example, there are no contact shadows nor reflective surfaces with elements in the background plate for example which would complicate matters, but none the less it's a real-world example of how I tackled one pretty simple shot for a film.
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