Lesson 2 : Lighting in CGI
Discussing lighting in Computer Graphics (CG) is of paramount importance. It not only contributes to creating moods, telling stories, and evoking emotions in virtual environments but is also crucial for achieving realistic visuals that immerse the audience. On a technical level, mastering CG lighting requires specialized expertise. Constantly evolving, this field blends creativity and technology, continually pushing the boundaries of visual expression in the digital realm. Thus, CG lighting stands as a central and exciting element of contemporary graphic design.
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Table of Contents
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1. Lighting and MaterialÂ
2. Light Sources Categories
3. Types of Light Sources
4. Lighting Techniques
5. Movie Analyses
6. SourcesÂ
1. Lighting and Material
Lighting and material models are essential components of how light interacts with objects in a 3D computer graphics scene. Understanding these concepts is fundamental for creating visually convincing renders.
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Light reflection models describe how light interacts with object surfaces. Here are some commonly used models:
Phong reflection model: The Phong Law, also known as the Phong reflection model, is a widely used lighting model in 3D computer graphics and computer graphics to simulate how light interacts with object surfaces. It was developed by computer scientist Bui-Tuong Phong in 1973. This law of light reflection is divided into three main components: diffuse reflection, specular reflection, and ambient reflection.
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Diffuse Reflection: Diffuse reflection represents light that is scattered uniformly in all directions from the surface of an object. It is responsible for the object's base color. The amount of diffuse light reflected depends on the angle between the direction of incident light and the surface's normal. The closer this angle is to 90 degrees, the weaker the diffuse reflection. In other words, surfaces facing the light source directly will have more intense diffuse reflection.
Specular Reflection: Specular reflection controls shiny or specular highlights on the surface of an object. It is responsible for the bright spots and sharp reflections that can be observed on smooth and glossy surfaces such as glass or metal. Specular reflection depends on the direction of incident light, the viewer's position, and the surface's roughness. Smoother surfaces produce sharper specular reflections.
Ambient Reflection: Ambient reflection is a less realistic component of the Phong model. It assumes that there is always a minimum amount of light present in the scene, regardless of the direction of incident light or the geometry of the surface. Ambient reflection is often used to prevent dark areas of objects from becoming completely black in poorly lit environments.
The sum of these three components yields the final color of a pixel on the object's surface. The Phong model is relatively simple to calculate, making it a popular choice for real-time rendering in video games and interactive applications. However, it may be less accurate than more complex models in simulating real light interactions, including phenomena like light refraction and dispersion. As a result, in contexts requiring a high degree of realism, other more sophisticated reflection models, such as the Cook-Torrance model, are often preferred.
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Blinn-Phong Model: Similar to the Phong model, it provides more efficient calculations for specular reflection, making it popular in many applications.
Cook-Torrance Model: The Cook-Torrance model represents a significant advancement compared to the Phong model, as it relies on more realistic physical principles to simulate light interactions. It is particularly well-suited for generating renders of complex materials, such as glass, metal, glossy plastic, and other highly reflective or rough surfaces. Due to its complexity, it is typically employed in professional 3D modeling and rendering software to produce high-quality visuals.
Material Properties
Materials have properties that determine their behavior under different lighting conditions. Here are some key properties:
Reflectance: This is a material's ability to reflect incident light. Some materials, like metals, have high reflectance, while others, like fabric, have more diffuse reflection.
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Transmission: This property pertains to a material's ability to allow light to pass through it. Transparent materials like glass have high transmission.
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Diffusion: This involves the scattering of light in all directions. Matte materials exhibit high diffusion, creating a soft, non-glossy appearance.
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Emission: Certain materials can emit their own light, making objects appear as light sources.
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Refraction: This relates to the bending of light as it passes through a transparent material, such as glass or water.
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Specularity: It is a material's ability to produce specular reflections, creating bright areas on the surface.
Interaction between Light and CGI Surfaces
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The interaction between light and surfaces results from material properties and reflection models. Choosing the right reflection model for a given material and adjusting its properties are crucial for achieving the desired visual appearance. By comprehending these principles, CGI artists can manipulate materials and lighting to create realistic and compelling 3D images. This profound understanding is essential for producing visually convincing renders in 3D computer graphics.
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We will delve into these topics in detail in the Lookdev lessons.
2. Light Sources Categories
Natural lights
Natural light is one of the most fundamental and versatile elements in filmmaking and photography. It refers to the illumination provided by the sun, the sky and the moon. Here are some key aspects of natural light:
Qualities of Natural Light: Natural light changes throughout the day, affecting its color temperature, intensity, and direction. It can range from soft and diffused during overcast conditions to harsh and direct in bright sunlight.
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Soft vs. Hard Light: Soft natural light occurs when the sun is diffused by clouds, creating a gentle and even illumination. Hard natural light is direct sunlight, which creates well-defined shadows and can be more challenging to work with.
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Color Temperature: Natural light's color temperature varies throughout the day. It is cooler in the morning and warmer during the golden hour. Understanding and utilizing these temperature changes can greatly influence the mood and atmosphere of a shot.
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Directionality: The angle at which natural light strikes a subject affects the appearance of the scene. Front lighting illuminates the subject directly, while side or backlighting can create depth and drama.
The "Dome Light" is a specific feature in RenderMan, the rendering engine developed by Pixar. It is used to simulate environmental lighting, particularly for creating image-based lighting (IBL), where the 3D environment is lit based on a background image (HDRI) or a spherical texture image.
The Night In CGI
The moon: In cinema, the moon is often treated with a blue tint, whereas in reality it is physically yellow. This result is often due to an artistic choice. The color blue can evoke a sense of mystery, dream or science fiction, which may be appropriate for certain productions.
Lord of the ring (2001)
_-_Ringwraiths_Enter_Bree.webp)
As the moon is generally visible at night, the lighting of the scene can play a role in how it is depicted. To create a striking visual contrast with the night sky, the moon can be rendered in blue to stand out.
 Monstres Academy (2013) Pixar Studio
Artistic choices can be diverse, but in cinematography we like to play with these different hues. The example of the Monster Academy (2013) and the desaturated moon sequence is quite incredible. You can feel the sadness of the moment through the bland, colorless night.
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 Monstres Academy (2013) Pixar Studio
For example, in this scene from Pixar's Coco (2017), the character is lit only with pratical lights, while the candles bring rim light and a bit of warm color to the image, and the purple of the TV is the key light that illuminates the face.
Coco (2017) Pixar Studio
Here in Monstres Academy (2013), we see that the practical lights separate the background from the foreground. The background is blue lit by the moon (natural light) and the foreground is yellow-orange lit by the artificial lights. Here we also have a narrative purpose: Bob is sad, he was in the blue (sadness) and now he's in the yellow, which represents happiness and a good mood from his friends who want him to get better.
 Monstres Academy (2013) Pixar Studio
James Bond Skyfall (2012)
Natural light is a powerful tool in filmmaking and photography, offering a wide range of possibilities for creating compelling and evocative visuals.
Understanding its qualities and learning how to work with it effectively is a crucial skill for any visual storyteller.
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Pratical Lights
Practical lights, in the context of filmmaking, refer to actual light fixtures that are part of the scene and
serve a dual purpose: they provide illumination for the shot and they appear as part of the set or location.
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Here are some key points about practical lights:
Realism and Atmosphere: Practical lights add a sense of realism to a scene.
They can be lamps, overhead lights, candles, or any other source of light that might naturally exist in the environment. This helps create a believable atmosphere for the audience.
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Set Dressing: Practical lights are often used as part of the set design. They can be chosen for their aesthetic
appeal and how they fit into the overall visual design of the scene.
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Functional and Aesthetic: Practical lights serve both a functional and aesthetic purpose. They actually illuminate the scene, providing light for the actors and the camera. Additionally, they contribute to the overall look and feel of the shot.
Challenges of Practical Lights: While practical lights enhance realism, they can present challenges for the cinematographer. They may not provide enough light for a well-exposed shot, and the color temperature of practical lights may not match other lighting sources. Cinematographers often use additional lighting equipment to balance and enhance the practicals.
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Controlling Practical Lights: Sometimes, the intensity of practical lights needs to be controlled. This can be done by using dimmer switches or placing diffusion materials on or near the light source.
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Symbolism and Storytelling: The choice of practical lights can also carry symbolic meaning or contribute to the storytelling. For example, a single flickering candle can create an intimate and mysterious atmosphere.
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Mixing with Other Lights: Practical lights are often used in combination with other types of film lights, such as key lights,
fill lights, and backlights. This allows for greater control over the overall lighting setup.
Overall, practical lights play a significant role in creating a natural and immersive visual experience for the audience.
They add depth and texture to a scene, making it feel more lived-in and authentic.
Dramatic Lights
Dramatic lighting is a technique in cinematography and photography that emphasizes contrast, shadow, and highlights to create a visually striking and intense atmosphere. It is often used to evoke strong emotions and add depth to a scene. Here are some key aspects of dramatic lighting:
High Contrast: Dramatic lighting typically involves a significant contrast between the illuminated areas (highlights) and the shadowed areas. This creates a strong visual impact and can draw the viewer's attention to specific elements within the frame.
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Harsh Shadows: In dramatic lighting setups, shadows are typically well-defined and can be quite dark. This creates a sense of depth and dimensionality in the scene.
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Directional Lighting: The angle and direction of the light source play a crucial role in creating dramatic effects. Lighting from the side or at an angle can sculpt the subject and create interesting textures.
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Use of Key and Fill Lights: In dramatic lighting setups, the key light (the main light source) is often positioned in a way that creates strong contrasts. A fill light (a secondary light source) may be used to partially fill in shadows, but it is kept relatively low to maintain the dramatic effect.
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Color Temperature: The color temperature of the light source can be manipulated to enhance the dramatic effect. For example, using warmer tones (lower color temperature) can create a more intimate and intense atmosphere.
Psycho (1960)
The shower scene in Alfred Hitchcock's 1960 film "Psycho" is one of the most iconic scenes in the history of cinema. The lighting of this scene is essential in creating an atmosphere of tension and horror.
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One of the most striking features of the lighting in this scene is the high contrast between the bright and dark areas. The shower itself is brightly illuminated, creating dramatic shadows on the body of Janet Leigh (portrayed by Marion Crane). This extreme contrast adds to the intensity of the scene.
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The shot where the killer is seen features very dramatic lighting as we only see their silhouette, which enhances the mystery and dark aspect of the scene. It's one of the most well-known examples of dramatic lighting. In real life, the character would never have appeared so dark. The actor was painted black during filming, and laboratory touch-ups were used to achieve this result.
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Common Uses
Dramatic lighting is frequently seen in genres like film noir, horror, thrillers, and dramatic cinema. It is also used in portrait photography to create striking and impactful portraits.
Overall, dramatic lighting is a powerful tool in visual storytelling, allowing filmmakers and photographers to create scenes that are visually compelling and emotionally resonant. It can heighten the impact of a narrative and leave a lasting impression on the viewer.
3. Types of Light Sources
Key Light: The key light is the primary and most influential light source in a scene. It provides the main illumination on the subject. It is typically placed to one side of the subject, at an angle, and can be positioned above, below, or at eye level, depending on the desired effect. The key light defines the overall mood and establishes the direction of the shadows on the subject.
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Fill Light: The fill light is used to reduce the contrast between the highlights and shadows created by the key light. It "fills in" the shadows, providing a more even and balanced illumination. The intensity of the fill light is usually less than that of the key light. It is placed on the opposite side of the key light or at a different angle to soften the shadows.
Rim Light: The backlight is placed behind and slightly above the subject. It illuminates the edges of the subject, creating a subtle outline or halo effect. This technique separates the subject from the background, adding depth and dimensionality to the scene. It can also enhance the three-dimensionality of the subject.
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Bounce Light: Bounce light is indirect light that is redirected onto the subject using reflective surfaces. This technique softens shadows and provides a more natural and flattering illumination. A bounce board or a reflector can be used to bounce light from a source, such as a window or a studio light, onto the subject.
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3 points Lighting
Peaky Blinder (2020)
Gobo
A gobo is a stencil or pattern placed in front of a light source to create a specific shadow or shape on the subject or background. It can be used for dramatic or decorative effects.
Negative Fill: Negative fill involves blocking or absorbing light to create stronger shadows or areas of darkness. It is often used to add contrast and drama to a scene.
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Practical Effects: Practical effects involve using physical objects or techniques, such as smoke or fog to manipulate and enhance the way light interacts with the environment. These lighting techniques, when used skillfully and thoughtfully, allow cinematographers and photographers to control the mood, atmosphere, and visual impact of a scene, ultimately enhancing the storytelling experience for the audience.
4. Lighting Techniques
To create the right atmosphere in our scenes, we have access to several types of light. Let's discover the main sources used by Renderman and Arnold. These dazzling rendering engines have redefined the standards of the film, animation, and 3D design industry. RenderMan, developed by Pixar Animation Studios, and Arnold, crafted by Solid Angle, have successfully captured the hearts of artists and studios worldwide, thanks to their ability to transform virtual scenes into images of striking reality. Here are the different light majors :
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Dome Light / Skydome
Distant Light
Rectangle Light / Area Light
Sphere Light
Disk Light
Renderman Shelf
Arnold Shelf
Use HDRI with Dome Light
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What is a HDRI ?
High Dynamic Range Images (HDRI) are images that contain an extended range of luminance values. Unlike traditional images, HDRI captures a much broader range of brightness, spanning from very dark areas to very bright ones.
It's important not to use an HDRI with a sun, as we won't have full control over the sun. We'll simulate it with a Distant light instead.
Renderman Dome Light
Arnold Skydome
Dome Light Render
HDRI with Distant Light
The distant light corresponds to the sun, and we can adjust all the parameters as we wish. This is why we need an HDRI without a sun, for complete control over our lighting and intentions.
Distant Light
Distant Light in RenderMan are special light sources used to simulate light coming from distant sources, such as the sun or the moon, which emit parallel light.
Distante light and setting
Renderman set up Dome + Distante light
Dome Light + Distante lightÂ
SettingÂ
Here are the main parameters used for the distant light; you can refer to the RenderMan documentation for more details:
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Intensity: This parameter controls the brightness of the distant light. A higher value will increase the brightness of the light, while a lower value will decrease it.
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Exposure: Exposure adjusts the overall brightness of the light, which can be useful for controlling the dynamic range of the distant light.
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Color: You can specify the color of the distant light using this parameter. This allows you to give the light a specific hue; for example, sunlight can be yellow-orange.
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Direction: The direction of the distant light is crucial. You can specify the light's direction using a vector. This vector indicates the direction from which the light originates; for example, (0, 0, -1) indicates that the light comes from above and shines downward.
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Shadow: This parameter controls whether the distant light generates shadows in the scene. You can enable or disable shadows as needed.
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Specular Reflection (Réflexion spéculaire): You can enable or disable specular reflections caused by the distant light.
Rectangle Light / Area Light
The Rectangle Light (Renderman) / Aera Light (Arnold) is a light source that emits light in the form of a rectangle. It is particularly useful for simulating light sources such as neon lights, light panels, or rectangular windows in a scene. It's often the most commonly used light.
Rectangle + Area light
Render with Rectangle Light in RendermanÂ
Sphere Light
The Sphere Light in RenderMan is a light source that emits light omnidirectionally from a sphere. Unlike other types of lights, the Sphere Light emits light in all directions from its point of origin, thus creating ambient lighting in all directions.
Sphere Light
Render with Sphere Light in RendermanÂ
Disk Light
The Disk Light in RenderMan is a light source that emits light in a circular pattern from a disk. This light is designed to simulate light sources such as spotlights, headlights, or ceiling fixtures that emit light directionally and in a circular fashion.
Disk Light
Render with Disk Light in RendermanÂ
What's interesting about these types of lights like the rectangle, sphere, and disk in RenderMan is that we can access the light's Cone Angle and its Softness, which provides a lot of possibilities for lighting.
The Softness and Cone Angle parameters are essential features of lights in RenderMan, and they control how light propagates in a scene. Here are explanations of these parameters:
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Softness: The Softness parameter controls the softness of the shadows generated by the light. A higher softness value will result in softer and more diffused shadows, creating a more realistic and soft lighting effect. A lower value will produce sharp and hard shadows. You can think of it as the apparent size of the light source from the perspective of the illuminated object. A larger apparent light source produces softer shadows.
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Cone Angle: The Cone Angle parameter controls the direction in which the light is emitted. It specifies the angle from which the light is emitted from the light source. A large cone angle will emit light in a wide beam, while a small cone angle will limit it to a narrower and more directional beam. This allows you to simulate light sources like spotlights or projectors, where light is concentrated in a specific direction.
These parameters are particularly useful for adjusting the appearance and behavior of light in a scene, allowing you to create different lighting effects to match your artistic needs. By experimenting with softness and cone angle, you can achieve a variety of lighting effects, ranging from soft and diffused shadows to sharp and directional lighting. This adds flexibility to creating moods and atmospheres in your 3D renders.
Cone Angle 12.035
Softness : 0.00
Cone Angle 12.035
Softness : 0.6.31
Cone Angle 2.093
Softness : 0.965
This chart is a brief summary of the different lights and categories, and how they are named in the outliner:
Inspired by the chart by Chris Brejon
5. Movie Analyses
In this analysis, we delve into captivating sequences from cinema. Through a meticulous examination of the lighting, we will unveil the artistic choices that bring them to life. Every visual element contributes to creating an immersive experience. We will see the analysis of :
The dark knight (Interrogates the Joker)
Piper (short movie Pixar)
How to train your Dragon (making friends scene)
The Dark knight
Director of photography : Wally Pfister
The Dark Knight (2008), Warner Bros Studio
Let's see how light is treated here :
Extreme Contrast: The scene is characterized by a very strong contrast between the Joker and Batman. The Joker is illuminated from one side by an intense white light, highlighting his pale face and makeup. In contrast, Batman is immersed in darkness, leaving his face partially masked.
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Use of Natural and Artificial Light: The light comes from a combination of artificial sources, such as hanging lamps, and natural light from a window. This creates dynamic lighting that reinforces the tense atmosphere of the scene.
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Chiaroscuro Effect: The interrogation takes place in a semi-darkened room, with areas of shadow and light creating a chiaroscuro effect. This adds drama to the scene and heightens the intensity of the interaction between Batman and the Joker.
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Focus on Facial Expressions: The lighting particularly highlights the facial expressions of both characters. Every detail of the Joker and Batman's faces is visible, emphasizing the intensity of their confrontation.
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Use of Colors: The dominant colors are white and black, creating a striking contrast. The Joker's pallid face and smile stand out vividly, while Batman's dark costume blends into the shadows.
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Emotional Impact: The lighting contributes to intensifying the atmosphere of this crucial sequence. The interplay of light and shadow heightens the tension and underscores the duality between the Joker and Batman.
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In summary, the lighting in this scene is a crucial element in creating an intense and dramatic atmosphere. The strong contrast and expert use of light add visual depth to the confrontation between the Joker and Batman, thereby enhancing the emotional impact of this iconic sequence in The Dark Knight.
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Piper
Director of photography : Erik Smitt
Piper ( 2016), Pixar Studio Animation
Let's see how light is treated here :
Use of Natural Light: Piper is renowned for its impressive use of natural light. The scenes primarily take place outdoors, under the sunlight, creating a warm and luminous atmosphere. This reinforces the sense of realism and proximity to the natural environment.
Water Reflections and Refractions: Water plays a central role in this short film, and the Pixar team beautifully captured the reflections and refractions of light on the water's surface. This adds a visual complexity and enhances the realism of the aquatic environment.
Soft and Diffuse Lighting: The light is often soft and diffuse, creating a soothing and gentle atmosphere. This contributes to the visual aesthetic of the film and gives the impression of a peaceful day at the beach.
Use of Shadow for Drama: While most of the light is soft and diffuse, there are moments where shadow is used to create suspense and intrigue. For instance, when Piper explores the underwater depths, the darkness builds tension that is later relieved when she discovers the luminous shells.
Play of Light and Color: The moments where Piper interacts with the luminous shells are particularly striking. The variations in color and light create a fairy-tale and magical ambiance, contrasting with the realism of the rest of the short film.
Focus on Details: The lighting highlights the meticulous details of Piper's feathers and the shells. This adds a dimension of realism and authenticity to the animation.
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The expert use of lighting in Pixar's Piper greatly contributes to immersing the viewer in the world of this short film. The natural light and play of reflections add a level of visual sophistication, while the use of shadow and contrasts enhances the emotion and suspense of the story. It is an impressive demonstration of Pixar's mastery of lighting in animation.
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How to train Dragon
Director of photography : Roger Deakins and Gil Zimmerman
How to train your dragon (2010), Dreamworks Studio
Let's see how light is treated here :
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Atmosphere
Tension and Apprehension: The initial atmosphere is laden with tension and apprehension. Hiccup is visibly nervous about approaching the dragon, which is reflected in the overall ambiance of the scene.
Mystery and Wonder: The atmosphere is tinged with mystery as Hiccup explores this new and unfamiliar environment. The dragon represents something extraordinary and mysterious to him, adding an element of wonder to the scene.
Emotional and Tangible: The atmosphere is imbued with emotion, with Hiccup's curiosity, fear, and fascination clearly felt by the viewer. This makes the scene particularly engaging on an emotional level.
Initial Dark Atmosphere: The scene likely starts in a dark or semi-dark setting. This creates a sense of mystery and apprehension, emphasizing the unknown and the potential danger associated with the dragon.
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Lighting
Focused Lighting on the Characters: The lighting is directed towards Hiccup and the dragon, illuminating their faces and expressions. This creates a focal point on the interaction between the two, highlighting their budding connection.
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The color of the scene: the rosy hue of the scene evokes the passage of time, and harold stays close to the dragon for a long time. The lighting here indicates a temporal shift, like a timelapse. The pink tint brings softness, it's an emotional moment, a strong bond is being created, the color will help to feel a beautiful emotion. A soft, warm light could be used to express trust and mutual acceptance.
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Dynamic lighting effects: the dragon has luminous features (such as glowing eyes and scales), and lighting is used dynamically to accentuate these elements, underlining the creature's mysterious, fantastical side.
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Rim Light importante: at the end, when Hiccup manages to touch the dragon, a light rim links them. What's really interesting is that Hiccup isn't looking at the dragon, he's in the shadows. The rim is very symbolic here, creating the link that is being established.
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In conclusion, the lighting in this scene from How to Train Your Dragon plays an essential role in creating an immersive and emotional atmosphere. It contributes to illuminating the encounter between Hiccup and the dragon, underscoring the significance of this pivotal moment in the story.
How to train your dragon (2010), Dreamworks Studio
I hope this lesson has served you well !
6. SOURCES
Sources
https://en.wikipedia.org/wiki/Phong_reflection_model#/
https://inria.hal.science/hal-01515948
https://rmanwiki.pixar.com/display/RFK22/RenderMan+For+Katana+22.0
https://chrisbrejon.com/cg-cinematography/chapter-4-light-categories/
http://www.cs.sjsu.edu/~bruce/fall_2016_cs_116a_lecture_light_and_color_part_1_of_2.html
https://rmanwiki.pixar.com/display/REN/PxrGoboLightFilter
https://renderman.pixar.com/
https://taskercode.wordpress.com/tutorials/opengl-primer/tutorial-7-lighting/
Images
https://en.wikipedia.org/wiki/Phong_reflection_model#/media/File:Phong_components_version_4.png
https://en.wikipedia.org/wiki/Blinn%E2%80%93Phong_reflection_model#/media/File:Blinn_phong_comparison.png
https://inria.hal.science/hal-01515948
https://helpx.adobe.com/se/substance-3d-stager/using/add-materials-and-textures.html
https://renderman.pixar.com/resources/RenderMan_20/rfhEnvLights.html
https://www.rollingstone.fr/coco-pixar-de-lautre-cote-du-miroir/
https://doodleimprovement.tumblr.com/post/171319398629/my-favorite-scene-of-coco
http://www.cs.sjsu.edu/~bruce/fall_2016_cs_116a_lecture_light_and_color_part_1_of_2.html
https://ew.com/25-days-of-bond/
https://www.pinterest.co.uk/pin/348395721157569202/
https://www.distractify.com/p/what-are-they-smoking-in-peaky-blinders
https://www.ageofarmour.com/3d/tutorials/AoA_advanced_spot_light_help.html
https://rmanwiki.pixar.com/display/REN/PxrGoboLightFilter
https://taskercode.wordpress.com/tutorials/opengl-primer/tutorial-7-lighting/