Materials - Transparency in Blender

7/30/2019 Materials - Transparency in Blender

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From BlenderWiki

Transparency

Mode: All Modes

Panel: Shading/Material Context Transparency

Materials in Blender can be set to be transparent, so that light can pass through any objects using the material.

Transparency is controlled using an "alpha" channel, where eachpixel has an additional value, range 0-1, in addition to

its RGB color values. Ifalpha=0, then the pixel is transparent, and the RGB values for the surface contribute nothing to

the pixel's appearance; for alpha=1, the surface is fully opaque, and the color ofthe surface determines the final color

ofthe pixel.

In Blender, there are three ways in which the transparency ofamaterial canbe set: Mask, Z-Buffer and Ray-trace. Each ofthese is

explained in more detail below. The Material Preview option with a

sphere object gives a good demonstration ofthe capabilities ofthese

three options.

Common Options

The following property controls are available for all transparency options:

Alpha

Sets the transparency ofthe material by setting all pixels in the alpha channel to the given value.

Fresnel

Sets the power ofthe Fresnel effect. The Fresnel effect controls how transparent the material is, depending on

the angle between the surface normal and the viewing direction. Typically, the larger the angle, the more opaque

a material becomes (this generally occurs on the outline ofthe object).

Specular-

Controls the alpha/fallofffor the specular color.

BlendControls the blending between transparent and non-transparent areas. Only used ifFresnel is greater than 0.

Mask

This option simply masks the Background. It uses the alpha channel to mix the color ofeachpixel on the active object

plane with the color ofthe corresponding background pixel, according to the alpha channel ofthe pixel. Thus for alpha

= 1, the object color is seen - the object is completely opaque; but ifalpha = 0, only the background is seen - the

object is transparent (but note that any other object behind the active object disappears).

This is useful for making textures ofsolid or semi-transparent objects fromphotographic reference material - a mask is

made with alpha opaque for pixels within the object, and transparent for pixels outside the object.

See Mask Trans arenc .


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The Transparency Panel.

Z Buffer

This uses the alpha buffer for transparent faces. The alpha value ofeach pixel determines the mix ofthe basic color of

the material, and the color ofthe pixel is determined fromthe objects/background behind it. Onlybasic settings are

available with this option; it does not calculate refractions.

Raytraced Transparency

Uses ray tracing to calculate refractions. Ray tracing allows for complex refractions, falloff, and blurring, and is used for

simulating the refraction oflight rays through a transparent material, like a lens.

Note that the RayTrace option is only available in the Blender Render and Cycles render engines, but not in the Game

Engine.

A ray is sent fromthe camera and travels through the scene until it encounters an object. Ifthe first object hit by the ray

is non-transparent, then the ray takes the color ofthe object.

Ifthe object is transparent, then the ray continues its path through it to the next object, and so on, until a non-

transparent object is finally encountered which gives the whole chain ofrays its color. Eventually, the first transparent

object inherits the colors ofits background, proportional to its Alpha value (and the Alpha value ofeach transparent

Material hit in between).

But while the ray travels through the transparent object, it can be deflected fromits course according to the Index of

Refraction (IOR) ofthe material. When you actually look through a plain sphere ofglass, you will notice that the

background is upside-down and distorted: this is all because ofthe Index ofRefraction ofglass.

Enable Raytracing

To get ray-traced transparency, you need to:

1. enable ray tracing in your Render settings. This is done in the Render context Shading Panel. Ray tracing is

enabled by default.

2. set your Alpha value to something other than 1.0.

3. in order for the background material to receive light passing through your transparent object, Receive

Transparent must be turned on for that material in the Material Shadow panel.

Options

In addition to the common options given above, the following property controls are

available:

IOR

Index ofRefraction. Sets how much a ray traveling through the material will

be refracted, hence producing a distorted image ofits background. See IOR

values for Common Materials below.

Filter


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Amount offiltering for transparent ray trace. The higher this value, the more

the base color ofthe material will show. The material will still be transparent but it will start to take on the color

ofthe material. Disabled (0.0) by default.

Falloff

How fast light is absorbed as it passes through the material. Gives 'depth' and 'thickness' to glass.

Limit

Materials thicker than this are not transparent. This is used to control the threshold after which the filter color

starts to come into play.Depth

Sets the maximum number oftransparent surfaces a single ray can travel through. There is no typical value.

Transparent objects outside the Depth range will be rendered pitchblack ifviewed through the transparent

object that the Depth is set for. In other words, ifyou notice black areas on the surface ofa transparent object,

the solution is probably to increase its Depth value (this is a common issue with ray tracing transparent objects).

You may also need to turn on transparent shadows on the background object.

Gloss

Settings for the glossiness ofthe material.

Amount

The clarity ofthe refraction. Set this to something lower than zero to get a blurry refraction.

Threshold

Threshold for adaptive sampling. Ifa sample contributes less than this amount (as a percentage), sampling

is stopped.

Samples

Number ofcone samples averaged for blurry refraction.

Examples

Index of Refraction

(Influence ofthe IOR ofan Object on the distortion ofthe background:

spheres ofWater, Glass and Diamond(top to bottom).). There are different

values for typical materials: Air is 1.000 (no refraction), Alcohol is 1.329, Glass is

1.517, Plastic is 1.460, Water is 1.333 and Diamond is 2.417.


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Influence ofthe IOR ofan

Object on the distortion ofthe

background: spheres of Water,

Glass and Diamond (top to

bottom).

Fresnel

16 pieces ofglass rotated in various directions demonstrate the angle-dependent Fresnel effect with ray-traced (left)

and alpha buffered transparency (right). Note that the major difference is the lack ofIOR effect in the latter case.

(Download .blend.)

Settings for Fresnel using ray-traced (left) and Z transparency (right).

Note the specular highlight in the F4 glass tile (which is facing midway between the light and the camera); the Fresnel

effect canbe seen in row C and column 6 where the faces are turned away fromthe camera.

The amount ofFresnel effect canbe controlled by either increasing the Blend value or decreasing the Alpha value.


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A simple scene with three glasses on a surface, and three lamps. Depth was set to 4, 8, 12, and 14, resulting

in render times of 24 sec, 34 sec, 6 min, and 11 min respectively. (Download .blend.)

Depth

Increasing Depth also considerably increases render time. Each time a light raypasses through a surface, the ray-

tracing algorithm is called recursively. In the example above, each side ofeach glass has an exterior and an interiorsurface. Light rays thus have to pass through four surfaces for each glass.

But not only that, at everypoint on a surface, some ofthe light can be reflected, or mirrored offthe surface in various

directions. This results in multiple rays needing to be calculated for eachpoint (often referred to as a tree ofrays[1]

(http://www.cs.unc.edu/~rademach/xroads-RT/RTarticle.html) ). In each ofthe rendered images above there are

640400=256 000 pixels. By increasing Depth, at least one tree ofrays is added to each pixel.

Be kind to your computer. Carefully placing objects in a scene to avoid overlapping transparent objects is often an

interesting alternative.

Hints

Transparent shadows

No transparent shadows No transparent shadows, environment lighting enabled


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Transparent shadows enabled, alpha set to 0.0 As previous, alpha set to 0.25

Transparent shadows with ambient occlusion set to

multiply, distance 1 (radius ofsphere)

As previous, distance increased to 2 (diameter of

sphere)

By default, the shadows oftransparent objects are rendered solid black, as ifthe object was not transparent at all. But

in reality, the more transparent an object is, the lighter its shadow will be.

In Blender, transparent shadows are set on the materials that receive the shadows fromthe transparent object. This is

enabled and disabled with the Receive Transparent button, in the Material context Shadow panel. The shadow's

brightness is dependent on the Alpha value ofthe shadow casting material.

Alternatives to transparent ray-traced shadows canbe found in the World context, namely the Ambient Occlusion,

Environment Lighting, and Gather panels. Alternatively, a texture canbe used to control the Intensity value ofthe

shadow-receiving material.

IOR values for Common Materials

The following list provides some index ofrefraction values to use when ray-traced transparency is used for various

liquids, solids (gems), and gases:

A

Acetone 1.36

Actinolite 1.618

Agalmatolite 1.550

Agate 1.544

Agate 1.540

Air 1.000

E

Ebonite 1.66

Ekanite 1.600

Elaeolite 1.532

Emerald1.560 -

1.605

1.560 -

J

Jade, Jadeite1.64 -

1.667

Jade, Nephrite 1.600 -1.641

Jadeite 1.665

Jasper 1.540

S

Sanidine 1.522

Sapphire1.757 -

1.779

Sapphire, Star1.760 -

1.773

Scapolite 1.540


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Alcohol 1.329

Alcohol, Ethyl

(grain)1.36

Alexandrite 1.745

Alexandrite 1.750

Almandine 1.83

Aluminum 1.44Amber 1.545

Amblygonite 1.611

Amethyst 1.540

Ammolite 1.600

Anatase 2.490

Andalusite 1.640

Anhydrite 1.571

Apatite 1.632

Apophyllite 1.536

Aquamarine 1.575

Aragonite 1.530

Argon 1.000281

Asphalt 1.635

Axinite1.674 -

1.704

Axinite 1.675

Azurite 1.730

B

Barite 1.636

Barytocalcite 1.684

Beer 1.345

Benitoite 1.757

Benzene 1.501

Beryl1.57 -

1.60

Beryl, Red1.570 -

1.598

Beryllonite 1.553

Brazilianite 1.603

Bromine (liq) 1.661

Bronze 1.18

Brownite 1.567

C

Calcite 1.486

Calspar 1.486

Cancrinite 1.491

Carbon

Emerald Catseye 1.605

Emerald, Synth

flux1.561

Emerald, Synth

hydro1.568

Enstatite 1.663

Epidote 1.733

Ethanol 1.36

Ethyl Alcohol 1.36

Euclase 1.652

F

Fabulite 2.409

Feldspar,

Adventurine1.532

Feldspar, Albite 1.525Feldspar,

Amazonite1.525

Feldspar,

Labradorite1.565

Feldspar,

Microcline1.525

Feldspar,

Oligoclase1.539

Flourite 1.434

Formica 1.47

G

Garnet, Andradite1.88 -

1.94

Garnet,

Demantoid

1.880 -

1.9

Garnet,

Demantoid1.880

Garnet, Grossular 1.738

Garnet, Hessonite 1.745

Garnet, Mandarin1.790 -

1.8

Garnet, Pyrope1.73 -

1.76

Garnet, Rhodolite1.740 -

1.770

Garnet, Rhodolite 1.760

Garnet,

Spessartite1.810

Garnet, Tsavorite1.739 -

1.744

Jet 1.660

K

Kornerupine 1.665

Kunzite1.660 -

1.676

Kyanite 1.715

L

Labradorite1.560 -

1.572

Lapis Gem 1.500

Lapis Lazuli1.50 -

1.55

Lazulite 1.615

Lead 2.01

Leucite 1.509

M

Magnesite 1.515

Malachite 1.655

Meerschaum 1.530

Mercury (liq) 1.62

Methanol 1.329

Milk 1.35

Moldavite 1.500

Moonstone 1.518 -1.526

Moonstone,

Adularia1.525

Moonstone,

Albite1.535

Morganite1.585 -

1.594

N

Natrolite 1.480

Nephrite 1.600

Nitrogen (gas) 1.000297

Nitrogen (liq) 1.2053

Nylon 1.53

O

Obsidian 1.489

Oil of

Wintergreen

1.536

Oil, Clove 1.535

Oil, Lemon 1.481

Oil, Neroli 1.482

Scapolite, Yellow 1.555

Scheelite 1.920

Selenium,

Amorphous2.92

Serpentine 1.560

Shampoo 1.362

Shell 1.530Silicon 4.24

Sillimanite 1.658

Silver 0.18

Sinhalite 1.699

Smaragdite 1.608

Smithsonite 1.621

Sodalite 1.483

Sodium Chloride 1.544

Spessartite1.79 -

1.81

Sphalerite 2.368

Sphene 1.885

Spinel1.712 -

1.717

Spinel, Blue1.712 -

1.747

Spinel, Red 1.708 -1.735

Spodumene 1.650

Star Ruby1.76 -

1.773

Staurolite 1.739

Steatite 1.539

Steel 2.50

Stichtite 1.520

Strontium Titanate 2.410

Styrofoam 1.595

Sugar Solution

30%1.38

Sugar Solution

80%1.49

Sulphur 1.960

Synthetic Spinel 1.730

TTaaffeite 1.720

Tantalite 2.240

Tanzanite1.690-


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Dioxide (gas) 1.000449

Carbon

Disulfide1.628

Carbon

Tetrachloride1.460

Carbonated

Beverages

1.34 -

1.356Cassiterite 1.997

Celestite 1.622

Cerussite 1.804

Ceylonite 1.770

Chalcedony1.544 -

1.553

Chalk 1.510

Chalybite 1.630

Chlorine (gas) 1.000768

Chlorine (liq) 1.385

Chrome Green 2.4

Chrome Red 2.42

Chrome

Tourmaline

1.61 -

1.64

Chrome Yellow 2.31

Chromium 2.97

Chrysoberyl 1.745

Chrysoberyl,

Cat's eye

1.746 -

1.755

Chrysocolla 1.500

Chrysoprase 1.534

Citrine1.532 -

1.554

Citrine 1.550

Clinohumite1.625 -

1.675

Clinozoisite 1.724

Cobalt Blue 1.74

Cobalt Green 1.97

Cobalt Violet 1.71

Colemanite 1.586

Copper 1.10

Copper Oxide 2.705

Coral 1.486

Coral1.486 -

1.658

Cordierite 1.540

Garnet, Uvarovite 1.74 -

1.87

Gaylussite 1.517

Glass 1.51714

Glass, Albite 1.4890

Glass, Crown 1.520

Glass, Crown,Zinc

1.517

Glass, Flint, Dense 1.66

Glass, Flint,

Heaviest1.89

Glass, Flint,

Heavy1.65548

Glass, Flint,

Lanthanum1.80

Glass, Flint, Light 1.58038Glass, Flint,

Medium1.62725

Glycerine 1.473

Gold 0.47

H

Hambergite 1.559

Hauyne1.490 -

1.505

Hauynite 1.502

Helium 1.000036

Hematite 2.940

Hemimorphite 1.614

Hiddenite 1.655

Honey, 13%

water content1.504

Honey, 17%

water content

1.494

Honey, 21%

water content1.484

Howlite 1.586

Hydrogen (gas) 1.000140

Hydrogen (liq) 1.0974

Hypersthene 1.670

I

Ice 1.309

Idocrase 1.713

Iodine Crystal 3.34

1.522 -

Oil, Orange 1.473

Oil, Safflower 1.466

Oil, vegetable

(50 C)1.47

Olivine 1.670

Onyx 1.486

Opal, Black 1.440 -1.460

Opal, Fire1.430 -

1.460

Opal, White1.440 -

1.460

Oregon

Sunstone

1.560 -

1.572

Oxygen (gas) 1.000276

Oxygen (liq) 1.221P

Padparadja1.760 -

1.773

Painite 1.787

Pearl 1.530

Periclase 1.740

Peridot1.635 -

1.690

Peristerite 1.525

Petalite 1.502

Phenakite 1.650

Phosgenite 2.117

Plastic 1.460

Plexiglas 1.50

Polystyrene 1.55

Prase 1.540

Prasiolite 1.540

Prehnite 1.610

Proustite 2.790

Purpurite 1.840

Pyrite 1.810

Pyrope 1.740

Q

Quartz1.544 -

1.553Quartz, Fused 1.45843

R

Rhodizite 1.690

1.7

Teflon 1.35

Thomsonite 1.530

Tiger eye 1.544

Topaz1.607 -

1.627

Topaz, Blue 1.610

Topaz, Imperial1.605 -

1.640

Topaz, Pink 1.620

Topaz, White 1.630

Topaz, Yellow 1.620

Tourmaline1.603 -

1.655

Tourmaline 1.624

Tourmaline, Blue1.61 -

1.64

Tourmaline,

Catseye

1.61 -

1.64

Tourmaline, Green1.61 -

1.64

Tourmaline,

Paraiba

1.61 -

1.65

Tourmaline, Red

1.61 -

1.64

Tremolite 1.600

Tugtupite 1.496

Turpentine 1.472

Turquoise 1.610

U

Ulexite 1.490

Uvarovite 1.870

V-WWardite 1.590

Variscite 1.550

Water (0 C) 1.33346

Water (100 C) 1.31766

Water (20 C) 1.33283

Water (gas) 1.000261

Water (35 C,

room temp)1.33157

Whisky 1.356

Willemite 1.690

Witherite 1.532


9/9

Corundum 1.766

Cranberry Juice

(25%)1.351

Crocoite 2.310

Crystal 2.000

Cuprite 2.850

D

Danburite1.627 -

1.641

Danburite 1.633

Diamond 2.417

Diopside 1.680

Dolomite 1.503

Dumortierite 1.686

Iolite 1.578

Iron 1.51

Ivory 1.540

Rhodochrisite 1.600

Rhodonite 1.735

Rock Salt 1.544

Rubber,

Natural1.5191

Ruby1.757 -

1.779Rum, White 1.361

Rutile 2.62

Vivianite 1.580

Vodka 1.363

Wulfenite 2.300

Z

Zincite 2.010

Zircon1.777 -

1.987Zircon, High 1.960

Zircon, Low 1.800

Zirconia, Cubic2.173 -

2.21

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Materials - Transparency in Blender