Documentation Talk:Reference Section 1.3

Text Streams

There are seven distinct text streams that POV-Ray uses for output. On some versions each stream is designated by a particular color. Text from these streams are displayed whenever it is appropriate so there is often an intermixing of the text. The distinction is only important if you choose to turn some of the streams off or to direct some of the streams to text files. On some systems you may be able to review the streams separately in their own scroll-back buffer.

Here is a description of each stream.

Banner: This stream displays the program's sign-on banner, copyright, contributor's list, and some help screens. It cannot be turned off or directed to a file because most of this text is displayed before any options or switches are read. Therefore you cannot use an option or switch to control it. There are switches which display the help screens. They are covered in section "Help Screen Switches".

Debug: This stream displays debugging messages. It was primarily designed for developers but this and other streams may also be used by the user to display messages from within their scene files. See section "Text Message Streams" for details on this feature. This stream may be turned off and/or directed to a text file.

Fatal: This stream displays fatal error messages. After displaying this text, POV-Ray will terminate. When the error is a scene parsing error, you may be shown several lines of scene text that leads up to the error. This stream may be turned off and/or directed to a text file.

Render: This stream displays information about what options you have specified to render the scene. It includes feedback on all of the major options such as scene name, resolution, animation settings, anti-aliasing and others. This stream may be turned off and/or directed to a text file.

Statistics: This stream displays statistics after a frame is rendered. It includes information about the number of rays traced, the length of time of the processing and other information. This stream may be turned off and/or directed to a text file.

Status: This stream displays one-line status messages that explain what POV-Ray is doing at the moment. On some systems this stream is displayed on a status line at the bottom of the screen. This stream cannot be directed to a file because there is generally no need to. The text displayed by the Verbose option or +V switch is output to this stream so that part of the status stream may be turned off.

Warning: This stream displays warning messages during the parsing of scene files and other warnings. Despite the warning, POV-Ray can continue to render the scene. You will be informed if POV-Ray has made any assumptions about your scene so that it can proceed. In general any time you see a warning, you should also assume that this means that future versions of POV-Ray will not allow the warned action. Therefore you should attempt to eliminate warning messages so your scene will be able to run in future versions of POV-Ray. This stream may be turned off and/or directed to a text file.

Console Text Output

Debug_Console=bool	Turn console display of debug info text on/off
+GD	Same as Debug_Console=On
-GD	Same as Debug_Console=Off
Fatal_Console=bool	Turn console display of fatal error text on/off
+GF	Same as Fatal_Console=On
-GF	Same as Fatal_Console=Off
Render_Console=bool	Turn console display of render info text on/off
+GR	Same as Render_Console=On
-GR	Same as Render_Console=Off
Statistic_Console=bool	Turn console display of statistic text on/off
+GS	Same as Statistic_Console=On
-GS	Same as Statistic_Console=Off
Warning_Console=bool	Turn console display of warning text on/off
+GW	Same as Warning_Console=On
-GW	Same as Warning_Console=Off
All_Console=bool	Turn on/off all debug, fatal, render, statistic and warning text to console.
+GA	Same as All_Console=On
-GA	Same as All_Console=Off

You may suppress the output to the console of the debug, fatal, render, statistic or warning text streams. For example the Statistic_Console=off option or the -GS switch can turn off the statistic stream. Using on or +GS you may turn it on again. You may also turn all five of these streams on or off at once using the All_Console option or +GA switch.

Note: that these options take effect immediately when specified. Obviously any error or warning messages that might occur before the option is read are not be affected.

Directing Text Streams to Files

Debug_File=true	Echo debug info text to DEBUG.OUT
Debug_File=false	Turn off file output of debug info
Debug_File=file	Echo debug info text to file
+GDfile	Both Debug_Console=On, Debug_File=file
-GDfile	Both Debug_Console=Off, Debug_File=file
Fatal_File=true	Echo fatal text to FATAL.OUT
Fatal_File=false	Turn off file output of fatal
Fatal_File=file	Echo fatal info text to file
+GFfile	Both Fatal_Console=On, Fatal_File=file
-GFfile	Both Fatal_Console=Off, Fatal_File=file
Render_File=true	Echo render info text to RENDER.OUT
Render_File=false	Turn off file output of render info
Render_File=file	Echo render info text to file
+GRfile	Both Render_Console=On, Render_File=file
-GRfile	Both Render_Console=Off, Render_File=file
Statistic_File=true	Echo statistic text to STATS.OUT
Statistic_File=false	Turn off file output of statistics
Statistic_File=file	Echo statistic text to file
+GSfile	Both Statistic_Console=On, Statistic_File=file
-GSfile	Both Statistic_Console=Off, Statistic_File=file
Warning_File=true	Echo warning info text to WARNING.OUT
Warning_File=false	Turn off file output of warning info
Warning_File=file	Echo warning info text to file
+GWfile	Both Warning_Console=On, Warning_File=file
-GWfile	Both Warning_Console=Off, Warning_File=file
All_File=true	Echo all debug, fatal, render, statistic, and warning text to ALLTEXT.OUT
All_File=false	Turn off file output of all debug, fatal, render, statistic, and warning text.
All_File=file	Echo all debug, fatal, render, statistic, and warning text to file
+GAfile	Both All_Console=On, All_File=file
-GAfile	Both All_Console=Off, All_File=file

You may direct a copy of the text streams to a text file for the debug, fatal, render, statistic, or warning text streams. For example the Statistic_File=s option or the +GSs switch. If the string s is true or any of the other valid true strings then that stream is redirected to a file with a default name. Valid true values are true, yes, on or 1. If the value is false the direction to a text file is turned off. Valid false values are false, no, off or 0. Any other string specified turns on file output and the string is interpreted as the output file name.

Similarly you may specify such a true, false or file name string after a switch such as +GSfile. You may also direct all five streams to the same file using the All_File option or +GA switch. You may not specify the same file for two or more streams because POV-Ray will fail when it tries to open or close the same file twice.

Note: that these options take effect immediately when specified. Obviously any error or warning messages that might occur before the option is read will not be affected.

Warning Level

Warning_Level=n	Allows you to turn off classes of warnings.
+WLn	Same as Warning_Level=n

Level 0 turns off all warnings. Level 5 turns off all language version related warnings. The default is level 10 and it enables all warnings. All other levels are reserved and should not be specified.

Help Screen Switches

-?	Show help screen 0 if this is the only switch

Note: there are no INI style equivalents to these options.

After displaying the help screens, POV-Ray terminates. Because some operating systems do not permit a question mark as a command line switch you may also use the +H switch.

Note: this switch is also used to specify the height of the image in pixels. Therefore the +H switch is only interpreted as a help switch if it is the only switch on the command line.

Graphical interface versions of POV-Ray such as Mac or Windows have extensive online help.

Tracing Options

There is more than one way to trace a ray. Sometimes there is a trade-off between quality and speed. Sometimes options designed to make tracing faster can slow things down. This section covers options that tell POV-Ray how to trace rays with the appropriate speed and quality settings.

Quality Settings

Quality=n	Set quality value to n (0 <= n <= 11)
+Qn	Same as Quality=n

The Quality=n option or +Qn switch allows you to specify the image rendering quality. You may choose to lower the quality for test rendering and raise it for final renders. The quality adjustments are made by eliminating some of the calculations that are normally performed. For example settings below 4 do not render shadows. Settings below 8 do not use reflection or refraction. The duplicate values allow for future expansion. The values correspond to the following quality levels:

0, 1	Just show quick colors. Use full ambient lighting only. Quick colors are used only at 5 or below.
2, 3	Show specified diffuse and ambient light.
4	Render shadows, but no extended lights.
5	Render shadows, including extended lights.
6, 7	Compute texture patterns, compute photons
8	Compute reflected, refracted, and transmitted rays.
9, 10, 11	Compute media and radiosity

The default is 9 if not specified.

Automatic Bounding Control

Bounding=bool	Turn bounding on/off
+MB	Turn bounding on; Set threshold to 25 or previous amount
-MB	Turn bounding off
Bounding_Threshold=n	Set bound threshold to n
+MBn	Turn bounding on; bound threshold to n
-MBn	Turn bounding off; set future threshold to n
Light_Buffer=bool	Turn light buffer on/off
+UL	Turn light buffer on
-UL	Turn light buffer off
Vista_Buffer=bool	Turn vista buffer on/off
+UV	Turn vista buffer on
-UV	Turn vista buffer off

POV-Ray uses a variety of spatial sub-division systems to speed up ray-object intersection tests. The primary system uses a hierarchy of nested bounding boxes. This system compartmentalizes all finite objects in a scene into invisible rectangular boxes that are arranged in a tree-like hierarchy. Before testing the objects within the bounding boxes the tree is descended and only those objects are tested whose bounds are hit by a ray. This can greatly improve rendering speed. However for scenes with only a few objects the overhead of using a bounding system is not worth the effort. The Bounding=off option or -MB switch allows you to force bounding off. The default value is on.

The Bounding_Threshold=n or +MBn switch allows you to set the minimum number of objects necessary before bounding is used. The default is +MB25 which means that if your scene has fewer than 25 objects POV-Ray will automatically turn bounding off because the overhead is not worth it. Generally it is a good idea to use a much lower threshold like +MB5.

Additionally POV-Ray uses systems known as vista buffers and light buffers to further speed things up. These systems only work when bounding is on and when there are a sufficient number of objects to meet the bounding threshold. The vista buffer is created by projecting the bounding box hierarchy onto the screen and determining the rectangular areas that are covered by each of the elements in the hierarchy. Only those objects whose rectangles enclose a given pixel are tested by the primary viewing ray. The vista buffer can only be used with perspective and orthographic cameras because they rely on a fixed viewpoint and a reasonable projection (i. e. straight lines have to stay straight lines after the projection).

The light buffer is created by enclosing each light source in an imaginary box and projecting the bounding box hierarchy onto each of its six sides. Since this relies on a fixed light source, light buffers will not be used for area lights.

Reflected and transmitted rays do not take advantage of the light and vista buffer.

The default settings are Vista_Buffer=on or +UV and Light_Buffer=on or +UL. The option to turn these features off is available to demonstrate their usefulness and as protection against unforeseen bugs which might exist in any of these bounding systems.

In general, any finite object and many types of CSG of finite objects will properly respond to this bounding system. In addition blobs and meshes use an additional internal bounding system. These systems are not affected by the above switch. They can be switched off using the appropriate syntax in the scene file (see "Blob" and "Mesh" for details).

Text objects are split into individual letters that are bounded using the bounding box hierarchy. Some CSG combinations of finite and infinite objects are also automatically bound. The end result is that you will rarely need to add manual bounding objects as was necessary in earlier versions of POV-Ray unless you use many infinite objects.

Removing User Bounding

Remove_Bounds=bool	Turn unnecessary bounds removal on/off
+UR	Turn unnecessary bounds removal on
-UR	Turn unnecessary bounds removal off
Split_Unions=bool	Turn split bounded unions on/off
+SU	Turn split bounded unions on
-SU	Turn split bounded unions off

Early versions of POV-Ray had no system of automatic bounding or spatial sub-division to speed up ray-object intersection tests. Users had to manually create bounding boxes to speed up the rendering. Since version 3.0, POV-Ray has had more sophisticated automatic bounding than any previous version. In many cases the manual bounding on older scenes is slower than the new automatic systems. Therefore POV-Ray removes manual bounding when it knows it will help. In rare instances you may want to keep manual bounding. Some older scenes incorrectly used bounding when they should have used clipping. If POV-Ray removes the bounds in these scenes the image will not look right. To turn off the automatic removal of manual bounds you should specify Remove_Bounds=off or use -UR. The default is Remove_Bounds=on.

One area where the jury is still out is the splitting of manually bounded unions. Unbounded unions are always split into their component parts so that automatic bounding works better. Most users do not bound unions because they know that doing so is usually slower. If you do manually bound a union we presume you really want it bound. For safety sake we do not presume to remove such bounds. If you want to remove manual bounds from unions you should specify Split_Unions=on or use +SU. The default is Split_Unions=off.

Anti-Aliasing Options

Antialias=bool	Turns anti-aliasing on/off
+A	Turns aa on with threshold 0.3 or previous amount
-A	Turns anti-aliasing off
Sampling_Method=n	Sets aa-sampling method (only 1 or 2 are valid)
+AMn	Same as Sampling_Method=n
Antialias_Threshold=n.n	Sets anti-aliasing threshold
+An.n	Sets aa on with aa-threshold at n.n
-An.n	Sets aa off (aa-threshold n.n in future)
Jitter=bool	Sets aa-jitter on/off
+J	Sets aa-jitter on with 1.0 or previous amount
-J	Sets aa-jitter off
Jitter_Amount=n.n	Sets aa-jitter amount to n.n. If n.n <= 0 aa-jitter is set off
+Jn.n	Sets aa-jitter on; jitter amount to n.n. If n.n <= 0 aa-jitter is set off
-Jn.n	Sets aa-jitter off (jitter amount n.n in future)
Antialias_Depth=n	Sets aa-depth (1 <= n <= 9)
+Rn	Same as Antialias_Depth=n

The ray-tracing process is in effect a discrete, digital sampling of the image with typically one sample per pixel. Such sampling can introduce a variety of errors. This includes a jagged, stair-step appearance in sloping or curved lines, a broken look for thin lines, moiré patterns of interference and lost detail or missing objects, which are so small they reside between adjacent pixels. The effect that is responsible for those errors is called aliasing.

Anti-aliasing is any technique used to help eliminate such errors or to reduce the negative impact they have on the image. In general, anti-aliasing makes the ray-traced image look smoother. The Antialias=on option or +A switch turns on POV-Ray's anti-aliasing system.

When anti-aliasing is turned on, POV-Ray attempts to reduce the errors by shooting more than one viewing ray into each pixel and averaging the results to determine the pixel's apparent color. This technique is called super-sampling and can improve the appearance of the final image but it drastically increases the time required to render a scene since many more calculations have to be done.

POV-Ray gives you the option to use one of two alternate super-sampling methods. The Sampling_Method=n option or +AMn switch selects either type 1 or type 2. Selecting one of those methods does not turn anti-aliasing on. This has to be done by using the +A command line switch or Antialias=on option.

Type 1 is an adaptive, non-recursive, super-sampling method. It is adaptive because not every pixel is super-sampled. Type 2 is an adaptive and recursive super-sampling method. It is recursive because the pixel is sub-divided and sub-sub-divided recursively. The adaptive nature of type 2 is the variable depth of recursion.

In the default, non-recursive method (+AM1), POV-Ray initially traces one ray per pixel. If the color of a pixel differs from its neighbors (to the left or above) by at least the set threshold value then the pixel is super-sampled by shooting a given, fixed number of additional rays. The default threshold is 0.3 but it may be changed using the Antialias_Threshold=n.n option. When the switches are used, the threshold may optionally follow the +A. For example +A0.1 turns anti-aliasing on and sets the threshold to 0.1.

The threshold comparison is computed as follows. If r1, g1, b1 and r2, g2, b2 are the rgb components of two pixels then the difference between pixels is computed by

diff = abs(r1-r2) + abs(g1-g2) + abs(b1-b2)

If this difference is greater than the threshold then both pixels are super-sampled. The rgb values are in the range from 0.0 to 1.0 thus the most two pixels can differ is 3.0. If the anti-aliasing threshold is 0.0 then every pixel is super-sampled. If the threshold is 3.0 then no anti-aliasing is done. Lower threshold means more anti-aliasing and less speed. Use anti-aliasing for your final version of a picture, not the rough draft. The lower the contrast, the lower the threshold should be. Higher contrast pictures can get away with higher tolerance values. Good values seem to be around 0.2 to 0.4.

When using the non-recursive method, the default number of super-samples is nine per pixel, located on a 3*3 grid. The Antialias_Depth=n option or +Rn switch controls the number of rows and columns of samples taken for a super-sampled pixel. For example +R4 would give 4*4=16 samples per pixel.

The second, adaptive, recursive super-sampling method starts by tracing four rays at the corners of each pixel. If the resulting colors differ more than the threshold amount additional samples will be taken. This is done recursively, i.e. the pixel is divided into four sub-pixels that are separately traced and tested for further subdivision. The advantage of this method is the reduced number of rays that have to be traced. Samples that are common among adjacent pixels and sub-pixels are stored and reused to avoid re-tracing of rays. The recursive character of this method makes the super-sampling concentrate on those parts of the pixel that are more likely to need super-sampling (see figure below).

The maximum number of subdivisions is specified by the Antialias_Depth=n option or +Rn switch. This is different from the adaptive, non-recursive method where the total number of super-samples is specified. A maximum number of n subdivisions results in a maximum number of samples per pixel that is given by the following table.

+Rn	Number of additional samples per super-sampled pixel for the non-recursive method +AM1	Maximum number of samples per super-sampled pixel for the recursive method +AM2
1	1	9
2	4	25
3	9	81
4	16	289
5	25	1089
6	36	4225
7	49	16641
8	64	66049
9	81	263169

Note: the maximum number of samples in the recursive case is hardly ever reached for a given pixel. If the recursive method is used with no anti-aliasing each pixel will be the average of the rays traced at its corners. In most cases a recursion level of three is sufficient.

Another way to reduce aliasing artefacts is to introduce noise into the sampling process. This is called jittering and works because the human visual system is much more forgiving to noise than it is to regular patterns. The location of the super-samples is jittered or wiggled a tiny amount when anti-aliasing is used. Jittering is used by default but it may be turned off with the Jitter=off option or -J switch. The amount of jittering can be set with the Jitter_Amount=n.n option. When using switches the jitter scale may be specified after the +Jn.n switch. For example +J0.5 uses half the normal jitter. The default amount of 1.0 is the maximum jitter which will insure that all super-samples remain inside the original pixel.

Note: the jittering noise is random and non-repeatable so you should avoid using jitter in animation sequences as the anti-aliased pixels will vary and flicker annoyingly from frame to frame.

If anti-aliasing is not used one sample per pixel is taken regardless of the super-sampling method specified.

Statistic_File changes in beta?

Has the Statistic_File option changed in beta? In 3.6 I have it set to a custom file path, but in 3.7 it says the "file cannot be found". SharkD 00:57, 22 June 2010 (UTC)