September 22, 2019

Rendering Terms


Familiarizing yourself with the language of rendering will help you as you improve your rendering skills. Use this resource when you need a quick reference point.

Alpha Channel: An Alpha Channel represents information added to a raster image to indicate where it is transparent.  SketchUp supports transparent PNG alpha channels. Many paint programs like Photoshop and Photoshop Elements also make it easy to add alpha channels. However, Windows Paint, and several other paint programs do not have this capability. The RpTools Alpha Channel wizard (a SketchUp plug-in) makes it easy to add an alpha channel to an existing raster image (saved on disk), by indicating a color in the existing image which is supposed to be transparent.

Ambient Light: Ambient Light is light applied to the entire scene.  Renderers, like IRendernXt, add ambient light to a scene to represent more realistic lighting effect without having to enter every actual light source.  You can highlight parts of an image with an actual light, and then use ambient light to provide a flat but usable illumination for the rest of the scene. Decreasing ambient light generally produces images with more contrast. Too much ambient light can make a rendered image seem flat, and too little can cause excessive contrast.  Indirect Lighting, whichcalculates the effect of light bouncing off of surfaces and illuminating other surfaces, can reduces the need for ambient light.

Anti-Aliasing: Anti-aliasing refers to the process of making edge lines look smoother by blending in the colors at the edges. SketchUp provides an option for anti-aliasing when saving a SketchUp model as a 2D image using “Export 2d Graphic”.  SketchUp anti-aliasing provides a slight improvement, but you will achieve a much better result if you save the image at 4X the desired size from SketchUp, then use an image editor to reduce its size and perform the anti-aliasing in the image editing program.

Batch Rendering:  When using a batch render feature you don’t need to be running SketchUp to process a rendering. You can close all other programs on your computer and dedicate your CPU processing power to render a / multiple scenes.

Biased:  A biased rendering engine will enable you to generate high-quality renderings quickly. For the highest quality renderings use an unbiased engine.

Bump Mapping: Bump Mapping refers to a rendering technique where a raster image, or procedural routine, is used to represent “bumps” on a surface. This change to the texture of a surface effects the illumination of that object when rendered, enhancing its 3D effect (without having to model the geometry). The source image itself is not rendered but is used to define changes in height of the surface.  Bump mapping is commonly used on water surfaces to add realism.

Caustics: Caustics refers to the bending and refraction of light when passing through transparent materials. Caustics can be set to change the way transparent objects treat light passing through them. The caustic effect produces focused light and shadow effects from a point light.

Clay Rendering: Clay Rendering is a gray scale rendering (without adding colors or textures) which is used to show the details of your model.  You can highlight the quality of a model with monochrome surfaces which do not distract from the model, and subtle lighting effects which bring outmodel detail.

Cove Lighting: Cove Lighting is a popular indirect lighting technique.  Lighting is pointed up to reflect off the ceiling to illuminate a space.  It’s ideal to generate soft and subtle lighting and shadows into your rendering.  However, cove lighting present a challenge for many renderers because the lights do not illuminate the scene directly, they must be processed as light reflected from the ceiling.

Depth of Field: Depth of Field and focal distance settings create renderings with some areas in sharp focus and other areas out of focus.

Edge Highlighting: Edge Highlighting can be used to bring out details on surfaces that would otherwise require the addition of geometry to the model to represent actual edge conditions. This is especially useful for cabinets or furniture where edge line highlighting helps bring out the detail of these components.  Some renderers do not perform edge highlighting.

Global Illumination: Similar to the terms Radiosity and Indirect Lighting, Global Illumination is a rendering term that refers to the process of accounting for the reflection of direct lights off illuminated surfaces.

Glow: Glow is an effect that allows you to define a material as if it were illuminated by lights, even if it is in a shadow, or the lights are dim as in a night scene. Glow can be applied to windows that are illuminated from the inside of a building, neon lights, or other lights, such as a car tail light, which would look photorealistic if they were self-illuminating, but do not need to cast light on nearby objects.  In other words, items with glow applied will seem brighter, but will not illuminate other items.

Examples include a vehicle headlight or a taillight that needs to have a lamp in it so that it can illuminate the road or other objects, but it might be sufficient to apply a glow material instead, or an object in your model which is backlit or produces its own illumination, such as a television set (if you wanted a television screen to illuminate a dark room, you would set it to be a light instead).  You can make an item glow brighter or look more realistic by adding self-glow from the material editor.

HDRi Images and Backgrounds: HDRi is the abbreviation for High Dynamic Range imaging. HDRi images provide a quick and accurate way to apply a high quality background image and illuminate a scene using the HDRi light intensity and colors.  One of the benefits of HDRi skies is that the background image is in the shape of a dome, providing a full 360 degree background. This means that no matter what angle you are viewing your model from, there will always be a high quality background image. This also makes them valuable for scenes containing reflective surfaces.

Image Filters: Image Filters are used to quickly apply a specific overall effect on your rendered image. Filter types found in some renderers include sharpen, smooth, soften, gamma, emboss, and gaussian.

Indirect Lighting: Indirect Lighting refers to the processing of light reflected from mirrors and other surfaces.  Indirect lighting can add subtlety and realism to an exterior rendering, including the undersides of overhanging features, such as eaves or balconies, which can be rendered more accurately.  Such subtlety comes at the cost of performance as more passes are required to resolve the image, and each pass takes longer, but the results are great.

Lighting Channels: During or after rendering, some renderers allow you to modify the image by changing the intensity of specific lights using a lighting channels or light balancer feature. You can adjust the intensity of the light sources, or save the lighting channel settings to reuse the same channels in future renderings.  Lighting channels enable you to quickly adjust the final rendering to get the lighting effects desired, adjust both the sun and sky to create dusk, or nighttime renderings, add ‘self glow’ to objects (such as TV monitors, or illuminates signs), and save time by not having to re-render after making lighting intensity changes.

Mirror: Mirror, or mirroring, is a process for making an identical, reversed copy of something.

Morphing: Morphing is the process of “Photoshopping” 3D renderings to appear more life-like.

Motion Blur: Motion blur makes objects appear blurry due to high-speed motion, or the motion of the camera.

Non-Photorealistic Rendering: Non-photorealistic rendering of scenes enables you to transform an image to look like a painting or drawing.

Normal: Each SketchUp face has a “normal” which is used to determine how light illuminates it. For most surfaces (surfaces which have not been smoothed), the normals are all perpendicular to the face.

OpenGL:  OpenGL (Open Graphics Library) is a standard specification defining a cross-language cross-platform API (Application Programming Interface) for writing applications that produce 2D and 3D computer graphics.

Panorama: Panorama refers to a full 360 x 360 degree image containing everything that can be viewed by a single camera position.  Once created, a panoramic image can be converted to a format for easy viewing, using the mouse to navigate.

Packet Mode: Packet Mode is a particular type of biased rendering engine, one of the fastest methods for creating renderings. It does this by making assumptions about light, reflection, and transparency. Unbiased engines use more precise algorithms that process each individual pixel, but early rendering passes are grainy (or noisy) until the solutions for adjacent pixels converge.

Perspective: Perspective is an approximate representation of an image as it is perceived by the eye.

Radiosity: Radiosity, like Indirect Lighting and Global Illumination, refers to the process of accounting for the reflection of direct lights off illuminated surfaces.  Radiosity simulates the many reflections of light around a scene, generally resulting in softer, more natural shadows.

Ray Trace: Ray Tracing is a general technique of rendering in which the lighting is determined by following rays of light as they interact with lights and other surfaces. It produces photorealistic results and facilitates more advanced optical effects, such as accurate simulations of reflection and refraction, and is efficient enough to be of practical use when such high quality output is sought.

Reflection: mirror-like or highly glossy reflection.

Refraction: Refraction is the bending of light associated with transparency.

Renderer: A renderer is a software program, and or video board firmware, which creates a 3D image from a 3D model.

Rendering: Rendering is the process of generating an image from a 3D model by means of a software program. A 3D model contains the geometry, viewpoint, texture and lighting information necessary to create the rendering.

Section Plane:  A section plane tool is used to create section cuts to enable you to view geometry within your model.

Self Glow: Self Glow illuminates a surface as if it had light shining on it, without actually making it a light. For objects which you want to appear bright, but which don’t need to illuminate other objects, this is much faster than making lights out of them.

Shading: Shading is how the color and brightness of a surface varies with lighting.

Shadows: Shadows are the effect resulting from the obstruction of light.

Soft Shadow:  A soft shadow is one with varying darkness caused by partially obscured light sources.

Solid Materials:  A solid material is one which appears to be carved out of a solid block, rather than just applied to faces of a sculpted object. SketchUp places materials on faces and allows for some mapping which wraps onto surfaces. However, for a realistic rendering from an object sculpted from wood, you will need to use a Ray Trace rendering engine.

Specular Reflection: Specular Reflection is the mirror-like reflection of light from a surface. Specular reflection on a shiny surface like tile or a wood floor can add to the realism of a 3D rendering.

Texture Mapping:  Texture mapping is a method of applying detail to surfaces.

Translucency:   Translucency is the ability for light to pass through a material that is not transparent.

Transparency: Transparency is the sharp transmission of light through solid objects.

Unbiased:  An unbiased rendering engine enables you to generate very high quality renderings which will take longer to resolve than renderings produced with a biased engine.

X-Ray:  X-Ray is a display style which renders your model with all surfaces transparent.  This make is easier to see items which are inside of other items, or which are behind other items.

Z-Fighting:  Z-fighting is where two faces are close together and you can see the hidden one through the visible one even though it should not be visible.  This happens when the computer renders the faces as if they were in the same location and it can’t decide which one should be viewed.