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The Power and the Glory

The Scope of Creative Control in the DI Process By Steve Wright


The introduction of computers to the color timing of feature films in the Digital Intermediate (DI) process has dramatically expanded the realm of creative possibilities during film finishing.  Color correction and image processing operations previously available only in telecine and computer graphics are now routinely applied to entire feature films.  Many of today's filmmakers are not computer experts and don't really want to become one, so following is a plainspoken description of the capabilities you can expect to find in today's well equipped DI suite. It is the story of the power of the computer and the glory of a beautiful film finish.

Basic Color Correction
The colorist has controls that he will call lift, gamma, and gain, but you will call them pure magic. By working these three controls in careful combination the colorist can affect the brightness and the color of the shadows, midtones, or the highlights - all separately. Shadows that were once blocked up can now be gently teased apart to reveal hidden detail, and even given a nightly blue hue. The midtones can be made brighter and/or warmer without disturbing the shadows or highlights. Hidden detail can be teased out of crushed highlights to give more life to a fire or an explosion.  The name of the game here is separation and control. In the example below (left) the shadows in the lower left corner are badly blocked up, obscuring a park bench in the background. The version on the right has had the dark detail restored revealing the park bench and even separating the cars and trees in the deep background with minimal effect on overall brightness.

Left image shows badly blocked up shadow detail. Right image shows expanded shadow detail.

The saturation control in DI is exactly what you have always wanted for those less than colorful shots.  Without altering brightness, contrast, or hue (unless you want to), the saturation can be increased until the picture looks like it is made of candy, desaturated completely to black and white, or anywhere in between. By increasing the contrast while removing some saturation a bleach bypass look can be "baked" into the negative which avoids costly special processing of all of the prints to get a similar look. The colorful carousel horse below shows how the same original clip can be wildly modified to produce a bleach bypass look at one extreme or a super saturated look on the other.


From left: Original Clip, Bleach Bypass Look, Super Saturated

Key Frame Color
Sometimes the lighting in a shot will change over the length of the cut. Maybe the camera pans from a brightly lit part of the scene to a dark area or perhaps someone turns on a light in a dark room, abruptly changing the lighting conditions. The digital colorist can adjust the color timing to one setting at the beginning of the shot (setting a key frame)  then a different setting at the end of the shot (setting a second key frame), then the computer will smoothly interpolate (change) between these two key frames. The colorist can actually set as many key frames in a scene as needed and the computer will gracefully slide from one color setting to the next keeping the color on track even in a changing scene. 

The Keys to the Kingdom
Another important feature found in the DI suite is the ability of the computer to generate keys (a machine generated matte) that can be used to isolate objects in the picture for separate treatment. There are two kinds of keys - Luma keys and Chroma keys.  The Luma key creates an isolation matte based on the brightness (luminance) of objects in the frame, whereas the chroma key creates a matte based on the color (chrominance) of objects. The "specifications" for a key can also be altered (key framed) over the length of a shot so that if, for example, the target object gets darker towards the end of the shot the key can still follow it.  Once a key is created, color corrections can be restricted to only the objects inside (or outside) of the key. In the example below, a luma key is created from the sky so it can be enhanced without effecting the foreground grass or the lighthouse.

From left: Original Clip, Luma Key for Sky, Enhanced Sky

How might this power to isolate objects based on their brightness or color be used? You might start out with fluffy white clouds, but they suddenly turn a bit pink after the shot is color timed. A luma key can isolate the clouds so that a desaturation operation can be applied just to them to restore them to a pristine white. Perhaps you have a beautifully exposed shot, but the skin tones are a bit sallow. A chroma key can "lock" onto the color of the skin so that a bit of red can be added to the flesh without effecting any other parts of the picture.  

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Related Keywords:digital intermediate, digital negative, film scanning, color timing, film finishing, digital mastering

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