24

Troubleshooting

You may encounter problems either during rendering (for example, rendering ends prematurely) or after rendering (for example, image quality is poor).

In This Section:

Common Rendering Problems

Rendering ends prematurely

Some common causes include:

  • Not enough memory.

See Optimization on page 495.

Reduce memory usage
  • Multiple instances of the same polyset with linked-lights and multiple shaders may cause the renderer to crash.
Copy the polysets instead of instancing them.

If either of these do not seem to be the cause of the problem, then do one or all of the following:

  • Render from the command line using the -N option. This turns on the diagnostic mode and notifies you of anomalies in the SDL file's global settings.
  • Open the .out file in the sdl directory. The problem may be as simple as a missing texture file.
  • Open the errlog file (File > Show > Errlog) and check for the message rendering error: exited with error code XXX. The XXX values are UNIX system error codes (not to be confused with internal error codes). The numbers come from the man page for signals (just type "man 5 signal"). Add 128 to the man page's numbers, and you get our exit code numbers. Out of memory is SIGUSR1, and the man page says its number is 16. Thus our exit code numbers read 128+16=144. Segmentation fault is 128+11=139, and so on.

Images that don't exist take a long time to load

The interactive package attempts to locate an image file in all directories specified by ALIAS_PIX_SEARCHPATH.

Reduce the number of directories in ALIAS_PIX_SEARCHPATH.

Rendering takes a long time

See Optimization on page 495.

Common Image Problems

Rendering ends normally, but image has problems. This section contains the following topics:

Shadows

Shadows produced from shadow casting have jagged shadow boundaries

Shadow map resolution is low.

Do one of the following:

  • Narrow the spread of the spot light so that it just barely covers the region you want lit. This provides a higher accuracy to the shadow map to work from. If you see banding artifacts, try increasing the Min Depth in the Self Shadow Correction section of the light's Control Window for the light's shadow.
  • Increase the resolution of the shadow map as a final resort. Remember, keeping large shadow maps increases memory usage.

Shadows from light fog may appear incorrect for very thin objects, or
Light fog shadows shift over an animation

See Fog samples on page 263.

Increase the Fog samples for the spot light.

Soft shadows produced by raytracing are noisy or jittery

Do one of the following:

See Use Shadow Map on page 246.

  • For spot lights, toggle Use Shadow Map ON so that the raycast shadows are used.

See Shadow Samples on page 246.

  • Increase Shadow Samples.

A dark moire pattern on a surface when raycasting, or
Incorrect shadows on a surface when raycasting

See Self Shadow Correction on page 263.

The renderer incorrectly believes that a surface is behind its shadow map.

Do one of the following:

See Min Depth on page 265.

  • Set Min Depth (in the Self Shadow Correction parameters) to a small positive number (in Alias grid units), for example 0.01, for shadow casting spot lights. This temporarily moves the surface (by the Min Depth value) when the renderer is calculating shadows. If Min Depth is too small, the surface will still be behind the shadow map. If Min Depth is too large, other surfaces that should be in the shadow may be moved in front of the shadow map. Perform a test render, and adjust Min Depth until shadows appear correct.

See Blend Offset on page 266.

  • Instead of using Min Depth (as above), use Blend Offset. This variable scales the amount it moves each point on the surface based on the shadow map samples.

Incorrect or jittered shadows for moving objects with motion blur

Shadows are not motion blurred. The renderer calculates an object's shadow map when the camera shutter is at midpoint. When the object moves, it may move behind its own shadow map.

Do one of the following:

See Shadows on page 423.

  • If the object has a separate face facing the shadow casting spot light, set Shadows off for that face (under Render Stats).

The new shadow map algorithm is not enabled by default because it has problems shadowing particles and light fog.

  • Use the new shadow map algorithm by including the following line in your SDL file for each spot light that casts shadows:
use_old_shadow_map_algorithm=FALSE

See Self Shadow Correction on page 263.

If objects are still moving fast enough to cause self- shadowing, increase Min Depth or Blend Offset (in the Self Shadow Correction parameters) for shadow casting spot lights.

Glows

Shader glow brightness changes during an animation, or
Shader glow brightness is different at different rendering resolutions

The shader glow auto exposure is adjusting the overall brightness of the scene for each frame. When a glowing object enters or exits the frame, the glow intensity of all objects will change.

The shader glow auto exposure causes a similar problem when rendering at different resolutions. For example, shader glow brightness will be different in a high resolution final render than in a low resolution test render.

Do one of the following:

See ShaderGlow on page 58.

  • Set Auto Exposure OFF (under the environment's ShaderGlow parameters), and adjust the environment shader's ShaderGlow Glow Intensity and Halo Intensity by hand until shader glows have the correct brightness.

See ShaderGlow on page 58.

  • Render the animation with Auto Exposure ON, and select a frame in which the shader glow brightness looks correct. Render that frame only, again with Auto Exposure ON. Open the out file (out.<name> in the sdl directory), and find the Glow intensity normalization factor and the Halo intensity normalization factor. Enter these two values in the environment shader's ShaderGlow Glow Intensity and Halo Intensity parameters, and set Auto Exposure OFF.
If you are also rendering at different resolutions, you must also scale these values based on the difference in resolutions (scale factor).

For example, if you are doubling the rendering resolution, the scale factor would be 2.
Alternatively, figure out the factor by which the *number* of pixels in the image increases, and multiply the glow by it.
i.e.: (1920 x 1280) / (720 x 486) = 7.023
Multiply your glow intensity by 7.023

Glow is missing from volume lights

Light from a volume light exists only within its volume. If the camera is not within this volume, then glow is not rendered.

Do one of the following:

  • Make sure that the camera is within the volume light boundary. Use Display > Tgl camera if necessary.
  • Create a glow-only point light at the same location as the volume light.

Linear and area lights shine through objects, or
Light glow shines through objects

Linear and area lights do not attempt to detect if there are shadowing objects between the light and the eye. All other light types compute this occlusion factor.

See Hide Source on page 82.

Create a shader glow object with the same shape as the light, and set Hide Source ON.

Light glow shines through objects

See Opacity on page 248.

Set Opacity to 0 for the light.

Light glow shines through objects

The radius of the light may be so large that it is never completely occluded by the object that should be shadowing it.

See Light Radius on page 244.

Check the Light Radius (under Common Parameters). The default setting is 1 (that is, two grid units in diameter). If Light Radius is large in relation to the geometry in the scene, reduce Light Radius to a value comparable to the size of the geometry.

Glows do not render

There is not enough memory for the renderer to calculate glows.

Do one of the following:

See Optimization on page 495.

  • Reduce memory usage.

See Hide Source on page 82.

  • Render glows separately. Set Hide Source ON under Glow parameters, and enter the command setenv SEPARATE_GLOW_FILES 1 in the render shell. Render the scene, and composite the two image files.

Aliasing

Jaggies or roping, noisy or jittered images, shimmer or moiré-banding over an animation

Not all aliasing artifacts are caused by the same limitations, nor are they resolved in the same manner. For example, increasing the Minimum and Maximum Anti-aliasing Levels will not solve the problem optimally. Types of aliasing include: geometry, textures, shadows, highlights, and motion blur.

Geometry

Geometry has jagged edges against the background

Composite Rendering may be ON.

Do one of the following:

See Composite Rendering on page 403.

  • Set Composite Rendering OFF (under Render Globals).

See Anti-aliasing Levels on page 401.

  • First increase Threshold under Render Globals. If the jagged edges persist, increase Minimum and Maximum Anti-aliasing Levels.

Textures

File textures are very noisy and not anti-aliased well, or
File textures appear to shift or shimmer over an animation

First check that the texture's Blurmult value is non-zero. Next, change the file texture's Filter type. The default setting is BLEND. The best compromise between speed and quality is QUADRATIC.

Procedural textures are very noisy and not anti-aliased well, or
Procedural textures appear to shift or shimmer over an animation

Do one of the following:

See Blur on page 102.

  • Increase the Blurmult and/or Bluroffset values for the texture.

See Curve Threshold on page 400.

  • Increase the Anti-aliasing Levels Curve Theshold value under Render Globals.

See Convert to Pix on page 104 and Filter on page 152.

  • Use Convert to Pix to convert the procedural texture to a file texture, and change the Filter type to QUADRATIC.

An in-focus object next to a blurry foreground/background (Depth of Field ON) shows a jaggy artifact

Render the blurry foreground/background separately, and composite.

Textures are distorted (stretched and/or squashed)

See Chord Length on page 147.

The surface may have uneven parameterization. Set Chord Length ON under the texture's Surface Placement parameters.

Motion Blur

Motion blur noise

Insufficient temporal sampling of shading and/or textures.

See MB Texture Samples on page 424.

If the texture looks grainy, increase MB Texture Samples (under Render Stats) for the object. This will marginally increase rendering time.

See MB Shading Samples on page 424.

If the specular looks noisy, increase MB Shading Samples (under Render Stats) for the object. This will noticeably increase rendering time; increase MB Shading Samples only when absolutely necessary.

Large objects do not motion blur correctly

A large object that stretches way beyond the view is clipped by the renderer. This clipping is done properly when the object is not motion blurred, but may clip incorrectly when the object is motion blurred.

See Object Rendering Parameters on page 422.

Increase the object tessellation by increasing either Minimum Subdiv and Maximum Subdiv (if Adaptive Subdiv is ON), or Uniform U and Uniform V (if Uniform Subdiv is ON) for the object in the Render Stats window.

Motion blur does not work

There are two possible causes:

  • If you are raytracing, this is a known limitation.

See Motion Blur on page 344.

  • If only the camera is animated, and nothing else (that is, a flyby), make sure that Motion Blur is ON for the camera (in the Camera Editor).

Rendering with motion blur produces grid-like artifacts, or
Rendering with motion blur causes triangles to disappear

Some large triangles may extend beyond the camera and near clipping planes. Objects may be too close together, causing interpenetrating problems for motion blur.

Increase the tessellation subdivision level for problem surfaces. Move surfaces that may be too close together further apart.

Spot light shadows and light projections do not motion blur

This is a known limitation.

For shadows, blur the shadow by decreasing the Resolution (under Shadow Casting parameters). For projector lights, apply a solid projection texture to the object rather than using the light projection.

Solid textures do not motion blur correctly

This is a known limitation. Surface textures motion blur correctly.

See Convert Solid Tex on page 26.

If the moving object is a patch or a polyset with u,v parameterization, use Convert Solid Tex and apply the pix file as a File texture.

See Project to UV - Apply Mapping on page 197.

If the moving object is a polyset without u,v parameterization (for example, a ViewPoint model), apply the solid texture as a Projection texture, and perform a Project to UV mapping (under the texture's Polyset Surface(U,V) Definition).

Warped objects do not motion blur when warp parameters are animated

When a warp parameter is animated, the resulting changes in the shape of the warped object are not motion blurred. An object moving through a warp will be motion blurred correctly.

Move the object relative to the warp.

Chatter in motion blurred textures moving behind transparent surfaces

Motion blurred textures moving behind transparent surfaces may show chatter in the texture.

See MB Shading Samples on page 424.

Increase MB Shading Samples for the transparent surface.

Motion blurred textures appear streaked or jittery

Motion blurred textures may appear streaked or jittery for fast moving objects.

Do one of the following:

See MB Texture Samples on page 424.

  • Increase MB Texture Samples for the textured surface.

See MB Shading Samples on page 424.

  • If the motion blur of specular highlights, bump maps or displacement maps is jittery, increase MB Shading Samples for the textured surface. This will increase rendering time, so try increasing MB Shading Samples by one for each test render until the streaks/jitter is eliminated.

Particles

Particles do not emit from faces, shells or stitched objects

This is a known limitation.

Particles render inconsistently

Particles may render inconsistently if Animation is OFF.

Do one of the following:

See Animation on page 397.

  • Set Animation ON (under Render Globals) before rendering.

See Use File on page 290 of this book, and Save Particles in the Animating in Alias book.

  • Create a particle file by setting Save Particles ON (under Run Dynamics), and then set Use File ON (under Particle Emission parameters) to use the particle file when rendering.

Particles emit incorrectly from convex polysets

This is a known limitation.

Rendering blobby surface particles with light fog produces artifacts

Type setenv ALIAS_LIGHTFOG_BLOBBY from the console window before launching Alias.

Rendering particles takes longer than previous versions of Alias.

Previous versions of Alias determined the rate of particle emission based on the amount of machine memory. This resulted in different renderings on machines with different memory configurations.

Particles are not generated

Particles are not calculated if the emitter is invisible on the start frame of rendering.

Do one of the following:

See Transparency on page 78.

  • Animate Transparency (in the shader's Common Parameters) instead of Visibility (in the Parameter Control window).

See Use File on page 290 of this book, and Save Particles in the Animating in Alias book.

  • With the object visible, create a particle file by setting Save Particles ON (under Run Dynamics). Make the object invisible, and set Use File ON (under Particle Emission parameters) to use the particle file when rendering.

Changing Emission or Behavior parameters, or the Parent Color parameter does not affect particles

Changing any Emission or Behavior parameters, or the Parent Color parameter, does not affect particles that have already been emitted, or particles that have already been generated and saved in a particle file.

In order to see the effect of any change in these parameters, you must run the simulation again (or invoke a batch render, which does its own run of the simulation).

Particles that overlap a transparent surface make the surface partly visible, or
Image planes or transparent objects do not render correctly when combined with fog and/or particles

This is a known limitation. If you are using particles, the problem may be caused if there is Blob Noise on the particles, or if the Render Type is BLOBBY SURFACE.

Do one of the following:

  • If you are using particles, and the particles have Blob Noise, try raycasting instead of raytracing. The transparency problem will be less noticeable.
  • If you are using particles, and the transparent surface is the particle emitter, create a particle file, and then move the transparent surface out of view. You may need to assign the particle file to a non-invisible dummy object for the particles to appear.

See Setting Keyframes for Isolated Animatable Properties in the Animating in Alias book.

  • If you are using particles, and the transparent surface is not the particle emitter, then animate its Visibility (in the Parameter Control window).
  • If you are using fog, try using a few very large particles instead of the fog effect.

See Attenuate Transp. (Attenuate Transparency) on page 410 and Opacity Depth on page 81.

  • Try turning Attenuate Transp. OFF under Render Globals and increasing Opacity Depth under the shader's Special Effects parameters.

Particles do not recompute over each odd and even field, only on each frame

This should not produce any clearly visible artifacts.

Particle Transparency has no effect

Particle Transparency may seem to have no effect when the Render Type is BLOBBY SURFACE, and the particles are either very large or very small. Because transparency is based on the depth of the blobby substance in world units, changing transparency may seem to have no effect, but it actually does.

Set particle Density to 1/particle Size. For example, if particle Size is 0.1, set particle Density to 10.

Particles with Parent Color ON do not have the correct parent color

If Parent Color is ON, the particle's actual color is determined by multiplying the emitting object's color by the particle Color parameter.

If you want the particles to have the exact same color as the emitting object, then make sure that the particle Color parameter is white.

Particles do not emit correctly from a displacement mapped surface

If a particle emitting surface is displacement mapped, the particles are emitted from the surface's original, non-displaced position.

Particles originating at the camera origin disappear

Particles may disappear when Surf Shading is set to a non-zero value and particles originate at the camera origin.

A rendering error occurs when particles collide with a surface

A rendering error may occur when motion blurred particles collide with a NURBS surface that has geometry collisions on.

Create a particle file, and then turn collision off for both the NURBS surface and the particle system before rendering.

Hair grows longer or lags behind when the emitting object moves

See Simulation substeps on page 418 and Hair Segments on page 301.

Set Simulation substeps in Render Globals to the same value as Hair Segments in Particle Properties.

Warps

Unable to pick a warped object

The object's bounding box is unwarped.

Use a larger marquee pick region.

Objects with both warps and displacement maps result in unexpected behavior

This is a known limitation.

Warped objects do not render properly

Warped objects with degree 1 patches along the patch edges may not render properly. Degree 1 patches are often generated from the Surfaces > Set planar- function when Trim Surface is selected in the option box.

Create a degree 3 plane, project the outline curves onto the geometry and trim the result.

Warps do not produce smooth surfaces

The warp may have sudden discontinuities in its field, and these discontinuities overlap the surface. For example, the twist warp preset (Objects > Warps > Twist) pushes a surface the most at the edges of the cylinder, however just beyond the edge of the cylinder, the warp is zero. A surface intersecting the edge will go from no warp to maximum warp across the span of a single triangle.

Use the Decay and Dropoff parameters to smooth these transitions. If this is insufficient to smooth the field, smooth the gradients by texturing the light's color (which affects the warp intensity).

Shadows on warped objects are incorrect or polygonal

See Warp Objects on page 319 and Object Rendering Parameters on page 422.

If Warp Objects is set to PIXEL_RES, change it to TRIANGLE_RES and increase the object's Minimum Subdiv and Maximum Subdiv (if Adaptive Subdiv is ON) or Uniform U and Uniform V (if Uniform Subdiv is ON) in the Render stats window.

Miscellaneous Object Problems

Roping artifacts on highlights

The hard-edged highlights that the standard Phong model produces (many times magnified by a noisy bump map).

See Shading Model on page 74 and Post Filter on page 407.

Use the Blinn shading model instead. Also try turning the Post Filter option ON in the Blur Effects section of the Render Globals window.

Transparent objects do not show the background when raytracing, or
Reflective objects do not reflect the background when raytracing

You may be using a 2D texture or image plane on the background. For raytraced images, you must use either a flat color or an environment map for the background for reflected/refracted rays to render correctly.

Use a Spherical or Ball environment with your texture or image applied to it.

Thin highlights have roping artifacts

This may be due to the hard-edged highlights that the standard Phong model produces (many times magnified by a noisy bump map).

Do one of the following:

See Shading Model on page 74.

  • Use the Blinn shading model.

See Post Filter on page 407.

  • Set Post Filter ON in Render Globals.

Blended surfaces do not render

If part of a blended surface is visible, and another part is invisible, the surface will not render. The invisible part of the surface is not written to the SDL file, so the blend cannot be regenerated for each frame.

Make all parts of a blended surface visible.

Displacement mapping does not work for layered shaders

Only the lowest available layered shader can apply a displacement map.

Create a single displacement map and apply it to the lowest layered shader.

Chord Length texture maps do not display correctly in Shade Wire mode

If a surface with uneven parameterization and a checker texture map with Chord length ON is Quick rendered, the texture looks even, as a result of the chord space conversion. However, if the Quick render window is closed, and the shaded wire icon in the icon of the texture is clicked on, the surface is displayed as though Chord spacing is OFF.

Instanced objects with worldspace texture mapping render incorrectly

This is a known limitation.

Copy the geometry rather than instance it.

Renderer does not recognize BOT (block oriented texture) files directly applied as texture maps

See Texture Caching on page 406.

Set Texture Caching ON under Render Globals.

Invisible instances of objects are visible

This is a known limitation.

Duplicate the object instead of instancing it.

Bump map using a file texture does not render as expected

If the file has an alpha channel, then the alpha channel is used for bump mapping. If the file does not have an alpha channel, the RGB color channels are converted into a grayscale using a luminance calculation, and then used for bump mapping.

Remove the alpha channel from the file texture.

Banding appears on low intensity objects

This is due to the 8-bit per color channel limitation.

Do one of the following:

  • Set Film Grain to 0.01 in the environment shader.
  • Alter the colors of the lights by random, fractional amounts from pure integer values. For example, change (255,255,255) to (254.3,255.2,254.9).

Templated objects rendered in an animated sequence become visible

This is a known limitation.

Overall Image Problems

Black borders (letter box) appears in render

The black borders define the film gate.

See Ignore Film Gate on page 413.

Set Ignore Film Gate ON under Render Globals.

The rendered image does not match the view in the modeling window or camera

There are several possible causes:

  • The rendering aspect ratio may be different than the modeling window aspect ratio.
Set the window resolution to be the same as the rendering resolution.
  • The camera's film offset may be less than or equal to the camera's film back size.
  • You may have used Render Active, and the dag items under the camera were not selected in whole.
  • You may be using motion path curves with knot multiplicity.

See Use result in the Animating in Alias book.

Rebuild the curve or select CurveTools > Use result from the Action Window.

Color banding in rendered image

See Film Grain on page 63.

Set Film Grain to 0.01 in the environment control window.

Overall image is too sharp

See Post Filter on page 407.

Set Post Filter ON under Render Globals, and set the Post Center, Post Adjacent and Post Diagonal parameters to 4,2,1.

Common Interface Problems

Interface problems include any problems you encounter with parts of the Alias interface that relate to Rendering (for example, the Multi-lister) or with specific types of rendering modes (for example, Quick Render). This section contains the following topics:

Quick Render

Glows and particles do not Quick render in the perspective magnify window

This is a known limitation.

Partial Quick Rendering Ignores Glow

If Persistence is toggled on (under Global Quick Rendering Parameters), and a partial (subregion) Quick render is done, the partial region ignores shader glow.

Click on the Quick render window to render the entire window.

Light glows do not quick render

This is a known limitation.

Render light glows using the batch renderers.

Shade Mode

Black dots appear on textured objects in toggle shade mode on an Indigo 2X

If Fast Options is OFF and Display textures is ON (under Toggle Shade Options), black dots may appear on the texture when the subdivided triangles are very small.

See Object Rendering Parameters on page 422.

Reduce the subdivision level for the problem surface by reducing either Minimum Subdiv and Maximum Subdiv (if Adaptive Subdiv is ON), or Uniform U and Uniform V (if Uniform Subdiv is ON).

Textures do not render correctly in Toggle Shade or Fast Render mode

See Quick Render Options on page 368.

Open the Global Quick Rendering Parameters window, make sure Textures is ON, and perform a quick render. Toggle Shade and Fast Render should now render textures correctly.

Volume lights do not render correctly in Toggle Shade mode

Volume lights are treated as point lights in Toggle Shade mode.

Modeler Wire

Polysets do not render correctly

This is a known limitation. Shaded wire only displays NURBS surfaces and faces correctly.

Fast Render

Fast Render does not load V7.0 RRFR files properly.

When updating RRFR from the interactive package, the camera view will also be updated in RRFR.

Powercaster/Powertracer

Multiple renders on the same multi-processor machine produces the message "/usr/temp/sgi_mp_rt_locks permission denied"

Use the command setenv ALIAS_PLACE_LOCKS_IN_SWAP.

Multi-lister

Super textures (Studio Paint 3D textures) don't display on shader swatches in the Multi-lister

The Multi-lister does not display actual super textures. Instead, it displays super textures with an icon resembling a layering of a stack of papers.

Numeric fields do not allow lateral, slider-like movement

Press the Alt key and drag the mouse in the numeric field.

Low resolution shader swatches are not displayed in the Multi-lister

Increase the resolution of the shader swatch.

Shader swatch color is not accurate

The shader swatch is only a preview of the final result. Colors may not be exactly as shown. Always perform test renders.

Flipbook

Flipbook does not display mask files

Use the utility fcheck in the common bin/ directory to display sequences of mask files.

Flipbook does not support negative file extensions

Always use positive integers for file extensions.



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