Advanced Maya Texturing and Lighting- P8 pdf

the outColor of the file node is connected to the inrgb of a smear node.. the outu of the smear node is connected to the offsetu of the place2dtexture node of a ramp texture node.. the o

the smear utility allows one texture to be distorted by another if smear is combined

with a ramp texture, it creates a stylized vision effect that might be appropriate for an

alien, a monster, or a robot For example, in Figure 6.24 a sequence of video images

is loaded into a File texture the use image sequence attribute is checked so that the

images are automatically loaded as the timeline moves forward the outColor of

the file node is connected to the inrgb of a smear node the outu of the smear node

is connected to the offsetu of the place2dtexture node of a ramp texture node the

outV of the smear node is also connected to the offsetV of the place2dtexture node of

the ramp node the outColor of the ramp node is finally connected to the outColor of

a surfaceshader material node, which is assigned to a primitive plane the ramp has

three handles: one red and two orange the higher the values are in the video image

bitmaps, the farther the smear node “pulls” the ramp down in the V direction For

instance, if a bitmap provides a pixel with rgB values 0.5, 0.5, 0.5, the ramp is pulled

downward so that the top rests at the center of the ramp field if a bitmap provides a

pixel with rgB values 0.9, 0.9, 0.9, the ramp is pulled downward so that the top rests

outColor inRgb

outColor outColor

Figure 6.24 An image sequence and a Ramp texture are combined with the Smear utility This scene is included on the CD as

smear.ma A QuickTime movie is included as smear.mov

internally, the smear utility converts the input rgB to HsV new uV nates are generated by plotting values on an HsV color wheel For another example of the smear utility, see the tutorial at the end of this chapter

coordi-Correcting Gamma

gamma correction is the adjustment of an image to compensate for the physical tations of a computer monitor With a monitor, the intensity (brightness) of a screen pixel does not linearly increase with the application of additional voltage Because of this, uncorrected images may appear inappropriately dark or washed-out gamma correction solves this by applying a complementary intensity curve to the image to negate the monitor’s intensity curve different operating systems apply gamma cor-rection in different ways, whether through hardware or software controls microsoft-based systems generally operate with a gamma value set to 2.2, whereas macintosh

systems operate with a gamma value set to of 1.8 some programs, like adobe

photo-shop, allow you to apply different gamma values to the system on the fly

gamma correction is applied to the image with the following standard formula:

new pixel value = image pixel value ^ (1.0 / gamma value)thus, if an image pixel has a value of 0.5, 0.5, 0.5 and the gamma value is set

to 2.2, the new pixel value, which is sent to the screen, is roughly 0.73, 0.73, 0.73

maya’s gamma Correct utility also applies the standard gamma formula:

outValue = value ^ (1.0 / Gamma)

in this case, the gamma Correct utility adjusts the values of the value input and outputs the result through outValue no other node is affected as a rule of thumb,

the higher the gamma attribute values are, the more washed out the mid-range values

become High- and low-range values (white whites and black blacks) are affected to a

lesser degree

an interesting side effect of the gamma Correct utility is the increase or decrease

of saturation For example, in Figure 6.25 face.tif is loaded into a File texture the

outColor of the file node is connected to the value of a gammaCorrect node as a test,

the outValue of the gammaCorrect node is connected to the inputs[0].color of a

lay-eredtexture node the gamma attribute of the gammaCorrect node is set to 0.5, 0.5,

0.5 as a result, the washed-out bitmap gains a good deal of saturation raising the

gamma above 1 would have the opposite effect—less saturation

outColor value

outValue inputs[0].color

Figure 6.25 A washed-out face bitmap is given extra saturation with a Gamma Correct utility This shading network

is included on the CD as gamma_correct.ma

to view the custom shading network, follow these steps:

1. open the gamma_correct.ma file from the Cd open the Hypershade window

2. switch to the utilities tab mmB-drag the gammaCorrect node into the work area

3. With the gammaCorrect node selected, click the input and output

Connec-tions button the network becomes visible

(for example, Gamma) These fields are read left to right when representing color (red, green, blue) or position (X, Y, Z) When one of these fields is used in a custom shading network, the connection is made

to a single channel of the attribute (for example, gammaX)

For example, in Figure 6.26 face_2.tif is loaded into a File texture the outColor of

the file node is connected to the value of a contrast node as a test, the outValue of the contrast node is connected to the inputs[0].color of a layeredtexture node the Con-trast attribute of the contrast node is set to 4, 4, 4 the Bias attribute is set to 0.4, 0.4, 0.4 the resulting image has extremely white whites and black blacks and few colors

in the mid-ranges

outColor value

outValue inputs[0].color

Figure 6.26 A washed-out face bitmap is given a great deal of contrast with the Contrast utility This shading network

is included on the CD as contrast.ma

a Contrast value of 1 and a Bias value of 0.5 leaves the texture unchanged

lowering the Contrast value reduces the contrast raising the Bias value darkens the texture overall

A Note on Sliders and Super-White

in maya, many sliders that include number fields can readjust themselves For instance,

a diffuse attribute slider normally runs from 0 to 1 However, if you enter 2 into the

field, the slider automatically readjusts itself to run between 0 and 4 For the diffuse attribute, higher values result in a predictably brighter surface other sliders, when pushed past their default range, will not display a perceptible change any maya color channel can exceed the standard bounds of 0 to 1 although it’s not possible to do this directly through the attribute editor, you can enter extra-high values into the fields of the Color Chooser window to do so, follow these steps:

1. in the attribute editor tab, click the color swatch of an attribute the Color Choose window opens

2. Choose either rgB or HsV from the color space drop-down menu if you choose rgB, enter a value into the red, green, or Blue field there is no practi-cal limit to the size of the number you enter if you choose HsV, enter a value into the Hue, saturation, or Value field although Hue and saturation accept large numbers, the Value field is generally the most useful for custom values

3. Click the accept button to close the window

uninten-Color attributes of a grid texture node are set to 0.5, 0.5, 0.5 in rgB, creating a solid

gray (see Figure 6.27) the outColor of the grid node is connected to the input1 of a

multiplydivide node (see Chapter 8 for a description) the output of the first

multiply-divide node is connected to the input1 of a second multiplymultiply-divide node the output

of the second multiplydivide node is connected to a blinn material node the input2

attribute of the first multiplydivide node is set to 4, 4, 4 the end result, as seen in the

second multiplydivide node, is an rgB color with values of 2, 2, 2 these

inappro-priately high values are often referred to as super-white From a practical standpoint,

maya simply clamps any color over 1.0 to 1.0 when rendering standard images even

though the rgB is 2, 2, 2, it’s rendered as if it’s 1, 1, 1 (as seen on the blinn icon)

nevertheless, the super-white values can cause problems with custom connections if

they are not taken into account Fortunately, the Clamp utility can solve this problem

(see the next section)

Super-white values

outColor

input1

output input1

output color

Figure 6.27 A shading network designed to test super-white values This network is included on the CD as superwhite.ma

to view the custom shading network, follow these steps:

1. open the superwhite.ma file from the Cd open the Hypershade window

2. switch to the utilities tab mmB-drag the multiplydivide1 node into the

work area

3. With the multiplydivide1node selected, click the input and output

Connec-tions button the network becomes visible

super-white values See Chapter 13 for details

defini-tion of video white (100 IRE units in YUV color space) and the RGB color space used by Maya and other digital-imaging programs Basically, Maya creates whites that are 9 percent above the color range that

a television can actually display For more details on color space and monitor calibration, see Chapter 1

For a discussion of 8-bit versus 16-bit rendering, see Chapter 10

Clamping Values

the Clamp utility is designed to keep a value within a particular range if a value is too low or too high, it “clamps” it as an example, table 6.2 shows what happens to inputr values if minr is set to 0.3 and maxr is set to 1.0

in this example, if the inputr value is less than 0.3, the outputr value is 0.3

if inputr is greater than 1.0, outputr is 1.0 if inputr is between 0.3 and 1.0, putr is the same value the Clamp utility has three inputs and three output channels (inputr, inputg, inputB, outputr, outputg, and outputB); you can connect single attributes to any of these otherwise, you can connect vector attributes directly to input or output in a similar fashion, min and max, which set the clamp range, are vector attributes that carry three channels each (minr, ming, minB, maxr, maxg, and maxB) you can enter negative or positive values into the min and max fields

of the Additional_Techniques.pdf file on the CD For an example of the Clamp utility used to create disco ball glitter, see Chapter 7

Reading Surface Luminance

during a render, the surface luminance utility automatically reads the luminance of every single rendered point on the surface assigned to a material that is part of the same shading network that is, the utility can determine the total amount of light a point on a polygon face receives and outputs a value from 0 to 1 that represents this

as an example, in Figure 6.28, a custom crosshatch material is applied to a medallion model the crosshatch pattern is generated by a ramp texture and a sur-face luminance utility

the outValue of a surfaceluminance node is connected to the colorentrylist[0]

position of a ramp texture node the colorentrylist[n].position attribute controls the

vertical position of a color handle in a ramp texture in this case, the surfaceluminance

node drives the black color handle up and down the ramp based on how much light

a surface point receives if a surface point receives the maximum amount of light, the

outValue of the surfaceluminance node is 1, which forces the black handle up to the

top of the ramp (leaving the entire ramp field white) if a surface point receives a little

light, the outValue is a lower value, which allows the black handle to stay low, thus

creating a mix of black and white within the ramp color field

outValue colorEntryList[0].position

outC olor outC olor

outUV

uvC oord

outUvFilterSiz

e uvFilterSiz e

Figure 6.28 A crosshatch material is created with a standard Ramp texture and a Surface

Luminance utility This material is included on the CD as crosshatch.ma A QuickTime

movie is included as crosshatch.mov

the ramp’s type attribute is set to uV ramp; this allows the pattern to repeat

on the surface vertically and horizontally the ramp’s interpolation attribute is set to

none, giving the rendered lines a hard edge the ramp’s noise attribute is set to 0.1

and noise Freq is set to 0.05 in order to give the lines some squiggle the ramp node

has a standard place2dtexture node with a repeat uV set to 25, 25 Higher repeat

values will produce finer lines the place2dtexture node also has its rotate Frame set

to 45 in order to angle the pattern last, the outColor of the ramp node is connected

to the outColor of a surfaceshader material node, which is assigned to the medallion

Additional_Techniques.pdf file on the CD In Section 6.2, a stylized metal is created with super-white values.

Chapter Tutorial: Creating a Custom Paint Material

in this tutorial, you will create a custom material that transforms a photo into a ized painting (see Figure 6.29) you will use the smear, remap Hsv, and Contrast utilities

styl-Figure 6.29 (Left) A digital photo (Right) The same photo after the application of a custom paint material.

1. Create a new maya scene open the Hypershade window

2. mmB-drag a new layered texture utility (located in the other textures tion of the Create maya nodes menu) into the work area

sec-3 mmB-drag two remap Hsv utilities (located in the Color utilities section of

the Create maya nodes menu) place them to the left on the layeredtexture node

use Figure 6.30 as a reference rename the top remapHsv node remapHsvA

rename the bottom remapHsv node remapHsvB.

4. Connect the outColor of remapHsva to inputs[1].color of the layeredtexture node (For a review of how to create custom connections, refer to the beginning

of this chapter.)

5. Connect the outColor of the remapHsvB to inputs[0].color of the texture node

Figure 6.30 The shading network of the custom paint material

6. select remapHsva and open its attribute editor tab Click the Color

check-ered map button and select a File texture from the Create render node dow a place2dtexture node is automatically created along with a file texture

win-node rename this place2dtexture node place2dTextureA rename the file node FileA.

7. select remapHsvB and open its attribute editor tab Click the Color checkered

map button and select a File texture from the Create render node window a second place2dtexture is automatically created along with a second file texture

node rename the new place2dtexture node place2dTextureB rename the new file node FileB.

8. select Filea and open its attribute editor tab Click the File Browse button

beside image name and choose greyhound.tif from the Chapter 6 textures folder on the Cd

9. select FileB and open its attribute editor tab Click the File Browse button

beside image name and choose greyhound.tif from the Chapter 6 textures folder on the Cd

10. mmB-drag a smear utility (located in the Color utilities section of the Create

maya nodes menu) into the work area place it to the left of place2dtextureB

11. Connect the outu of the smear node to the offsetu of place2dtextureB

Con-nect the outV of the smear node to the offsetV of place2dtextureB

12. select the smear node and open its attribute editor tab Click the in rgb

check-ered map button and choose a Fractal texture from the Create render node window a new place2dtexture node is automatically created name this latest

place2dtexture node place2dTextureC.

13. select the fractal node and open its attribute editor tab Change the amplitude

attribute to 0.7 and the threshold attribute to 0.2 this will wash out the

14. select place2dtextureC and open its attribute editor tab Change the repeat

uV attribute to 0.6, 0.6 When the repeat uV value is reduced, the blobs with the Fractal become larger; this, in turn, creates larger waves in the smear node’s distortion try different repeat uV values to see different variations of the effect

15. select remapHsva and open its attribute editor tab Change the Hue, ration, and Value gradients to roughly match the left side of Figure 6.31 to move points on a gradient, select the little circles and lmB-drag to insert new points, click inside the dark gray area of each gradient to delete a point, click the × box below it these adjustments are shifting the hue, saturation, and value of the undistorted greyhound bitmap

satu-Figure 6.31 (Left) The gradients of the remapHsvA node (Right) The gradients of the remapHsvB node.

16. select remapHsvB and open its attribute editor tab Change the Hue, tion, and Value gradients to roughly match the right side of Figure 6.31 these adjustments are shifting the hue, saturation, and value of the distorted grey-hound bitmap

satura-17. select the layeredtexture node and open its attribute editor tab Click the leftmost purple box this displays the options for remapHsvB Change the alpha attribute to 0.5 this allows a 50-50 mix between the remapHsva and remapHsvB nodes (the Blend mode attribute should be set to over.)

18. mmB-drag a Contrast utility (located in the Color utilities section of the

Cre-ate maya nodes menu) into the work area place it to the right of the texture node Connect the outColor of the layeredtexture node to the value of the contrast node

layered-19. mmB-drag a new Blinn material into the work area place it to the right of the

contrast node Connect the outValue of the contrast node to the color of the blinn node select the contrast node and open its attribute editor tab Change the Contrast attribute to 1.5, 1.5, 1.5 and the Bias attribute to 0.7, 0.7, 0.5

this adjusts the contrast of the layeredtexture node try different numbers to see different results

20. select place2dtextureB and open its attribute editor tab Change the translate

Frame attribute to 0, 0.1 this raises the FileB up a tiny amount in the V tion, which counteracts the downward pull of the smear node

direc-21. mmB-drag a Bump 2d utility (located in the general utilities section of the

Create maya nodes menu) into the work area Connect outalpha of FileB to the bumpValue of the bump2d node Connect outnormal of the bump2d to normalCamera of the blinn node since outnormal is not a default attribute of

a Blinn material, you will have to use the Connection editor select the bump2d node and open its attribute editor tab Change the Bump depth value to 0.3

this bump mapping will give the smear distortion a sense of thickness

22. the custom paint material is complete! assign the blinn material node to a

primitive nurBs plane; add a directional, point, or spot light and render out a test it should look similar to Figure 6.29 if you get stuck, a finished version of the material is saved as paint.ma in the Chapter 6 scene folder on the Cd

7

Sampler utilities can automate a render

They can evaluate every surface point for every frame and return unique values that other nodes can use At the same time, you can connect cameras, lights, and geometry for unique shading networks Along similar lines, the Studio Clear Coat plug-in utility creates surface qualities unavailable to standard materials

7

the Sampler info, light info, particle Sampler, and distance Between utilities can all

be described as samplers they sample surface points, object transforms, or particle transforms automatically throughout the duration of an animation You can find the Sampler info, light info, and distance Between utilities in the general utilities sec-tion of the create maya nodes menu in the hypershade window You can find the particle Sampler utility in the particle utilities section Before i discuss the Sampler info or light info utilities, however, a look at the ramp Shader material and a review

of coordinate space is warranted

A Review of the Ramp Shader Material

the ramp Shader material has a color input attribute that has light Angle, Facing Angle, Brightness, and normalized Brightness options (see Figure 7.1)

Figure 7.1 (Left) The Selected Color gradient and Color Input attribute of a Ramp Shader

material (Right) The resulting material assigned to a primitive sphere lit from screen right

To see a larger version of the gradient, click the large button to the gradient’s right This scene is included on the CD as ramp_shader.ma

the color input attribute allows the ramp Shader to sample different points along the Selected color gradient based on feedback from the environment with light Angle, the material compares the angle of the surface normal to the direction of the light if the angle between the two is small, a high value is returned and the right side of the gradient is sampled if the angle between the two is large, a small value is returned and the left side of the gradient is sampled on a technical level, the surface normal vector and the light direction vector are put through a dot product calculation, producing the cosine of the angle between the two vectors For a deeper discussion on vectors and vector math, see chapter 8

this technique is also used for the Facing Angle option, whereby the angle of the surface normal is compared to the camera direction the Brightness option, on the other hand, calculates the luminous intensity of a surface point if the surface receives the maximum amount of light, the right side of the gradient is sampled if the surface receives a moderate amount of light, the middle of the gradient is sampled the gradi-ent runs 0 to 1 from left to right the light Angle, Facing Angle, and Brightness cal-culations are normalized to fit to that scale

calculations cannot be fine-tuned Sampler info, light info, and Surface luminance

utilities solve this problem by functioning as separate nodes the Sampler info

util-ity replaces the Facing Angle option the light info utilutil-ity replaces the light Angle

option the Surface luminance utility, as detailed in the previous chapter, replaces

the Brightness option Although the normalized Brightness option normalizes all

the light intensities in the scene, its basic function is identical to Brightness and can

be replicated with the Surface luminance utility in a custom shading network most

important, the Sampler info, light info, and Surface luminance utilities provide a

wide array of supplementary attributes

Coordinate Space Refresher

in general, four coordinate spaces are used in 3d software—object, world, camera,

and screen the term coordinate space simply signifies a system that uses coordinates

to establish a position For a surface to be rendered, it must pass through the

follow-ing spaces in the followfollow-ing order:

Object space A polygon surface is defined by the position of its vertices relative to

its center By default, the center is at 0, 0, 0 in object space (sometimes called model

space) A nurBS spline has its origin point at 0, 0, 0 in object space the axes of a

surface in object space are rotated with the surface

World space world space represents the virtual “world” in which the animator

manip-ulates objects A surface is moved, rotated, and scaled in this space to do this, the

vertex positions defined in object space must be converted to positions in world space

through a world matrix A matrix is a table of values, generally laid out in rows and

columns

Camera space world space must be transformed into camera space (sometimes called

view space) in order to appear as if it is viewed from a particular position in maya’s

camera space, the camera is at 0, 0, 0 with an “up” vector of 0, 1, 0 (positive Y) while

looking down the negative Z axis

Screen space three-dimensional camera space must be “flattened” so that it can be

seen in 2d screen space on a monitor

in addition, maya uses local space, parametric space, and raster space local space (sometimes called parent space) is similar to object space, but uses the axes and

origin of a parent node this is feasible due to maya’s dAg node system (See the

sec-tion “A transform and Shape node refresher” later in this chapter.)

to determine the color of a particular pixel when rendering a surface assigned

to a material that uses a texture map, the renderer compares the parametric spaces

of both the texture and the surface texture and surface parametric spaces are

com-monly referred to as uV texture space For more information on uVs and uV texture

space, see chapter 9