Texture Mapping. Images from 3D Creative Magazine

Transcription

1 Texture Mapping Images from 3D Creative Magazine

2 Contents Introduction Definitions Light And Colour Surface Attributes Surface Attributes: Colour Surface Attributes: Shininess Surface Attributes: Specularity Surface Attributes: Transparency & Opacity Surface Attributes: Refraction Surface Attributes: Luminosity Map Channels Map Channel Types Procedural Textures Animated Textures Mapping Coordinates Tiling Face Mapping Comparing Face Mapping & Mapping Coordinates General Mapping Tips Reference

3 Introduction As with modelling, texture mapping has a major impact on the quality of your end product. Practice to be imperfect if realism is the aim. That is, aim to dirty up a scene. The choice of texture mapping techniques is critical in achieving the best outcome for the end product. Aim to spend an equal amount of time in applying maps as is spent on modelling.

4 Definitions Mapping (Texture Mapping): The process of developing & assigning material attributes to an object. By default objects in a 3D software package have a dull plastic appearance. Material: The term for all the different settings assigned to an object s surface. These are defined by a name, eg. Shiny Red Plastic, Tarnished Silver etc. They may also be called shaders. Surface Attributes: Basic material settings such as colour, shininess, transparency etc. Texture: A bitmap image that gives a material it s unique qualities not available through simple surface attributes eg. a scan of a block of wood. Can also be used to vary surface roughness, transparency, colour etc. Procedural: Mathematically defined texture to simulate a material.

5 Definitions Summary: Texture mapping is the process of making & using materials made up of surface attributes and/or textures that allows an object to appear to be something other than a default flat plastic.

6 Light And Colour At phong (see later) level rendering, or higher, the effects of three potentially different colour sources can be seen. This colour can also be affected by the colour of any light sources. Ambient Colour: The hue (colour) an object reflects when in shadow. Generally, a very dark shade of the diffuse colour. Diffuse Colour: The hue (colour) an object reflects when lit by a direct light source. Set in the material editing section of software. Specular Colour: The hue (colour) of any highlights on an object. Also set in the material editing section of software.

7 Light And Colour Light & Colour Example: Ambient: Colour of the object in shadow. Diffuse: Colour of the object s material. Specular: Colour of the highlights

8 Surface Attributes The most basic type of material settings are supported by virtually every 3D program. Attributes are set using sliding controls or type in boxes and have a preview feature to check material appearance. Most common attributes are colour, shininess, specularity, transparency, falloff, refraction & luminosity. The Slate Material Editor module of 3D Studio MAX showing surface attribute features & preview windows.

9 Surface Attributes: Colour Colour: The combination of 3 elements; hue, saturation & value. Hue (Chroma): Commonly referred to as the colour & determined by the light coming from an object. Saturation (Intensity): A measure of how concentrated the colour is, eg. Whether it s rich & full or weak & gray. Value: The lightness or darkness of a colour eg. A pastel pink or deep wine red. Most software allows a full 24 bit range of colour choices including 256 gray values. Set using RGB (red green blue) or HSV (hue saturation value) sliders. Many also allow an additional 8 bits of transparency in the colour range.

10 Surface Attributes: Colour A material s colour can usually be selected from one of 16.7 million colours including 256 levels of gray. In grayscale a value of 0 is black, 128 is a neutral gray & 255 is white.

11 Surface Attributes: Colour Note: Not all colours can be duplicated by RGB and HSV models, especially strong yellows. The reason is the difference between the subtractive colour model of real world and the additive colour model of the digital world. Subtractive Colour: The 3 primary colours of red, yellow & blue when mixed together make a muddy brown. Additive Colour: The core colours of red, green & blue when mixed together make white. Gamut: The colour range of a colour model. The gamut of the colour models is therefore not identical. In addition, colour of most physical objects is made by light reflecting off objects into our eyes. In computers light is made within the monitor for each pixel s colour frequency.

12 Surface Attributes: Shininess Shininess: A measure of how glossy an object surface is. Works together with specularity to give the viewer information about a surface s reflectivity and material characteristics. Effect Of Shininess At 0% the material is matte while 100% is maximum glossiness. The specular highlight of the material shrinks as object is made glossier.

13 Surface Attributes: Specularity Specularity: Adjusts the intensity of the object s highlight if it has one. Specular highlights are the bright light reflections seen on glossy objects in Phong level rendering or above. It is related to the shininess of the object. Effect Of Specularity: Works with shininess to define an object s glossiness. Also plays a major role in simulating metallic materials.

14 Surface Attributes: Transparency & Opacity Transparency & Opacity: Controls the amount of light that can pass through a material. Transparency at 100% or opacity at 0% results in material being virtually invisible. Opposite values result in completely opaque material. Other values result in degrees of translucency. Transparent effects may not always look realistic if ray tracing not supported due to refraction problems. Additional settings such as filtered, additive & subtractive materials can be used.

15 Surface Attributes: Transparency & Opacity Transparency Effects: Control of amount of background image to be seen.!00% transparent is almost invisible except for any specular highlights. Transparency Types: Translucent portions can be affected by additive or subtractive settings. Subtractive darkens RGB values of filtered images & additive lightens them.

16 Surface Attributes: Refraction Refraction: The amount of light bent when it passes through a translucent object. It simulates the bending of light in nature when passing through different materials. Only supported in programs that allow ray tracing but can be simulated using refraction mapping.

17 Surface Attributes: Refraction Refraction Falloff: Controls how much more or less transparent an object is at its centre compared to its edges. It can be either inward or outward. Refraction Setting: Known as the Index of Refraction. Adjusts the amount that light is bent when passing through an object. A setting of 1.0 has no effect and higher values increase bending.

18 Surface Attributes: Luminosity Luminosity (Self Illumination): How much an object appears to be lit from within. As value increases it flattens out the effects of ambient & diffuse light sources. Has no effect on specular highlights. Luminosity Effects: 0% is completely unlit while 100% is totally self illuminated.

19 Map Channels Textures or procedural maps are used to bring more realism to materials over surface attributes that may be used in isolation. Textures be derived from scanned images, 2d paint images, mathematical processes or any other method that can generate an image or pattern. They fall into four basic categories: diffuse, bump, reflection & opacity. Others may be shininess, specularity, luminosity & refraction. Some channels only use the grayscale values of an image.

20 Map Channels Map channels usually have sliders or percentage values to adjust amount of effect. Some programs allow multiple maps in a channel allowing map blending to occur. You may also to do things such as masking, multiplying images, subtracting images etc. to achieve complex effects. Maps consume memory and slow rendering time and also need mapping co-ordinates in order to know where to be placed.

21 Map Channels The 3D Studio MAX map channel dialogue box for a standard material showing the range of attributes that can utilised using bitmap or procedural maps.

22 Map Channel Types

23 Map Channel Types Diffuse: Generally in colour & used to alter an object s colour to a pattern or image. Amount of change can be varied with 100% value completely overriding the base colour. Effective diffuse mapping uses a max. value of 90% as nothing in reality is fully saturated. To simulate a wood material on an object the diffuse map would be a scan or painting of wood grain. Bump: varying the surface roughness according to a grayscale image. Uses the lightness or darkness of a map to work out which section is protruding, flush or indented. With wood the bump map is a grayscale of the diffuse map making the grain (darker) appear indented.

24 Map Channel Types Reflection: Used to create an environment for a reflective object and roughly simulates the effects of ray tracing. It does this by overlaying a secondary diffuse map to give the impression the object is reflecting the scene contained in the image. To simulate chrome trim on an outdoor surface a reflection map of a cloudy sky is usually applied. Opacity: Grayscale images that override the transparency setting of a material. Can be used where dirty glass is wiped clean in parts or to put holes in objects without altering mesh.

25 Map Channel Types Shininess: Used to adjust the reflectivity of the surface to which it is applied and overrides any Shininess surface attribute settings. With a wood surface the same grayscale used for the bump map can be used to vary surface shininess as grain under a surface coating is less reflective. Specularity: Used to vary the colour & intensity of the specular highlights of the surface. Can be used to simulate materials like metals or metallic paint that reflects light in a spectrum (range) of colours & intensities.

26 Map Channel Types Self illumination: Grayscale maps used to create the impression that some parts of the object are lit from within. Can be used to map a stained glass lampshade to make glass panels appear to be lit while not affecting the lead that holds them together. Refraction: A means of simulating the effects of light refraction in programs not supporting ray tracing. The amount of refraction is based on the grayscale values in the image and the percentage control.

27 Procedural Textures Mathematically defined textures that can be used to overcome memory problems with bitmapped based texture maps. Can be used to create things such as wood grain & marble, for randomised or fractal patterns and for creating snow, rock & gaseous nebulae etc. Advantages over bitmapped textures: Consume less memory, don t need mapping coordinates, go right through an object so Boolean operations show a formed interior texture, and are easily animated such as for wind, smoke, mist or water. Disadvantages: May not always look as realistic as bitmap based texture maps.

28 Procedural Textures One of most useful function is for noise or mathematically derived static. For example, using fractal noise for bump & specularity mapping to turn a flat surface into a carpeted one.

29 Animated Textures The use of video or animation files instead of still images to change the texture of an object over time. Examples such as moving images on a TV or the change from daylight to night. Animation will loop if sequence being rendered is longer than animated texture.

30 Mapping Coordinates Mapping Coordinates: A set of co-ordinates that specify the location, scale & orientation of any texture maps applied to an object. Software systems need mapping co-ordinates to know where to apply any textures in a material. There is a relationship between mapping co-ordinates and the co-ordinates of an image applied as a texture map.

31 Tiling Tiling: A method of repeating an image over a large area. Only really works with seamless images.

32 Face Mapping Face Mapping: Mapping that ignores any mapping coordinates and tries to conform the image to pairs of faces that share an edge. Useful for objects with a fairly even size and face distribution and with a seamless texture.

33 Comparing Face Mapping & Mapping Coordinates A comparison of mapping coordinates to tiled or face mapping. With the same non-seamless texture applied tiling is seen on the face mapped object while the map stretches the image over the whole object in the other.

34 General Mapping Tips Complex objects can be difficult to apply effective mapping coordinates. You will need to use a UV Unwrap method to flatten geometry Use dirt and wear to give objects added realism and vary specularity maps Separating faces on a section of an object lets you apply custom details. If unable to do the above create small polygon objects such as a box or plane and apply an opacity map to make unneeded parts transparent. Allow as much time for texture mapping as for modelling of geometry. Aim to use maps wherever possible over building complex geometry.

35 General Mapping Tips Do test renders where camera comes close to an object to check degree of resolution of the texture map. As a starting point in texture mapping, render from a plan or elevation view. If modelling for a low polygon count, e.g. for a game, construct models and mapping at high resolution and use these as basis for low resolution version. Results in smoother looking maps. Ensure mapping coordinates are applied relative to the front surface of the object, otherwise bump maps will appear to stick out rather than recede.

36 Reference Source data & cover images from 3D Graphics & Animation by Mark Giambruno. Additional data from 3D Studio MAX help files.