about this project
This project, created for the Virtual Production course at RTVE Instituto, outlines the process for integrating a character into a city-to-forest scene transition using Chroma Key technique, detailing visual elements, chroma setup, lighting, and the use of tools such as Ultimatte 12. It also analyzes the choice between pre-key and post-key, emphasizing the importance of post-production to control lighting, color, and effects.
Visual Elements Definition
To ensure a smooth integration of the character with the environment during the transition from the city to the forest, we defined the following elements in the background and foreground.
Transition from City to Forest
- The pavement progressively transforms into dirt, with cracks and loose leaves.
- The buildings in the background gradually fade away and trees appear in their place.
- Vehicles in the foreground disappear and are replaced by logs and rocks.
Urban Scenario
Background:
- Rows of buildings lined up in side perspective
- Urban decorations such as lampposts, traffic lights and billboards.
Foreground:
- Moving vehicles (cars, buses) passing from left to right.
- Additional urban elements such as litter garbage cans, benches or electric poles.
Natural Scenery (Forest)
Background:
- Tall trees and dense vegetation in the background.
- More natural ambient light, with dynamic shadows of the foliage.
Foreground:
- Trees, roots and branches framing the foreground.
- More detailed rocks and vegetation to reinforce depth.
Chroma Keying Methods
Since the pre-key and post-key have different applications, we must analyze which one best fits this film production.
Pre-key (Chroma Key with external software, such as Ultimatte 12)
This method allows the green background to be extracted in real time during the shooting, but the final composition is adjusted in post-production.
Advantages:
- Facilitates on-set previsualization, improving direction and performance.
- High quality chroma key extraction.
- Allows detailed adjustments in post-production.
- Standard method in film, combining live visualization with post retouching.
Disadvantages:
- Requires manual corrections in post-production.
- Requires additional equipment such as Ultimatte 12.
- Errors in preview if lighting is not optimal.
Post-key (Chroma Key in real time with Unreal Engine, ICVFX, etc.)
Keying and compositing are performed in real time, generating the final image during the recording.
Advantages:
- Ideal for live productions, eliminating the need for post-production.
- Reduced editing time by generating the final image on set.
- Less workload in post-production.
Disadvantages:
- Less correction margin in postproduction.
- Possible errors in real time that cannot be corrected later.
- Requires powerful hardware to process keying without failures.
In addition to choosing between Pre-key or Post-key, we will compare different chroma key extraction software to select the most suitable option for the project.
To do so, we will compare software based on key criteria such as price, quality and chroma key extraction accuracy.
Choice of method for the scene
Since this is a film production and not a live event, the best choice for this scene is pre-key with Ultimatte 12.
Zero Density is also a strong option, but Ultimatte 12 gives us more control in post production without relying completely on realtime processing.
Justification
Greater control in post: Transitioning from an urban environment to an outdoor space requires detailed lighting, color and effects adjustments. With pre-key, we can make these changes without limitations.
Optimization of shooting without compromising later adjustments: On-set visualization is maintained without losing the ability to refine keying and composition in post.
Standard use in film: This method is the most widely used in film productions because of its balance between preview and control.
Implementation of the Chosen Method
Chroma Key Configuration
Background choice: Use of a uniform green cyclorama with controlled light absorption.
Chroma key material: Matte paint or cloth with tight tension to avoid wrinkles and reflections.
Set spacing: Sufficient distance between subject and background to avoid shadows or color contamination.
Lighting
Background: Homogeneous lighting with soft highlights to avoid color variations.
Character: Separate lighting with keylight and backlight to improve chroma separation.
Spill control: Use of clipping lights and reflectors to minimize green contamination on skin and clothing.
Physical Camera and Tracking
Camera: A high resolution sensor camera will be used to capture details without compression artifacts.
Tracking:
- Markers are placed on the ground and on key objects to correctly align effects in post-production.
- An optical or mechanical tracking system is used depending on the complexity of the scene.
Genlock and Timecode configuration
Genlock: Synchronization of multiple cameras and tracking systems to ensure frame-accurate alignment of frames and avoid misalignments in post-production.
Timecode: Ensures that digital capture and post-production effects match frame by frame.
Visual Example
Scene Description
The character walks in a straight line from left to right while the camera follows him with a horizontal tracking shot. Initially, he is in a crowded city, with skyscrapers in the background and urban decorations such as lampposts, litter garbage cans and moving vehicles, both in background and foreground. The environment is subtly transformed: the pavement becomes more rustic and small details such as leaves on the ground or changes in ambient light appear, indicating a progressive transition.
At a key moment, a bus passes in front of the camera, completely covering the character's view. Just as it crosses, the scenery changes completely: the character is now in a forest, with dense vegetation and completely different lighting.
It has been difficult to find reference images to show exactly what I want to convey and how to do it, thanks
and how to do it, thanks to a project I knew, I was able to identify how to show it.
Developed Competencies
- Scene Planning & Visual Composition: Designing and detailing the transition between environments (city to forest) with precise foreground and background elements.
- Technical Decision-Making: Comparing chroma keying methods (pre-key vs. post-key) and selecting the optimal solution for cinematic quality and control.
- Chroma Key Setup & Lighting: Planning chroma key studio setup, lighting strategies to avoid color spill, and ensuring clean keying.
- Virtual Production Integration: Understanding the use of real-time engines (Unreal Engine) and external keying software (Ultimatte 12) for scene compositing.
- Camera & Tracking Configuration: Planning the use of high-resolution cameras, tracking systems, and synchronization tools (Genlock, Timecode) for seamless integration.
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Problem Solving & Resourcefulness: Identifying potential technical challenges and sourcing practical references and solutions to visualize complex transitions.
