Documentation Talk:Reference Section 1

Partial Output Options

Start_Column=n	Set first column to n pixels
Start_Column=0.n	Set first column to n percent of width
+SC0.n	Same as Start_Column
Start_Row=n	Set first row to n pixels
Start_Row=0.n	Set first row to n percent of height
+Sn	Same as Start_Row=n
+SR0.n or +S0.n	Same as Start_Row=0.n
End_Column=n	Set last column to n pixels
End_Column=0.n	Set last column to n percent of width
+EC0.n	Same as End_Column
End_Row=n	Set last row to n pixels
End_Row=0.n	Set last row to n percent of height
+En	Same as End_Row=n
+ER0.n or +E0.n	Same as End_Row=0.n

When doing test rendering it is often convenient to define a small, rectangular sub-section of the whole screen so you can quickly check out one area of the image. The Start_Row, End_Row, Start_Column and End_Column options allow you to define the subset area to be rendered. The default values are the full size of the image from (1,1) which is the upper left to (w,h) on the lower right where w and h are the Width=n and Height=n values you have set.

Note: if the number specified is greater than 1 then it is interpreted as an absolute row or column number in pixels. If it is a decimal value between 0.0 and 1.0 then it is interpreted as a percent of the total width or height of the image.

For example: Start_Row=0.75 and Start_Column=0.75 starts on a row 75% down from the top at a column 75% from the left. Thus it renders only the lower-right 25% of the image regardless of the specified width and height.

The +SR, +ER, +SC and +EC switches work in the same way as the corresponding INI-style settings for both absolute settings or percentages. Early versions of POV-Ray allowed only start and end rows to be specified with +Sn and +En so they are still supported in addition to +SR and +ER.

When rendering a subset of *columns* (+sc/+ec) POV-Ray generates a full width image and fills the not rendered columns with black pixels. This should not be a problem for any image reading program no matter what file format is used.

When rendering a subset of *rows* (+sr/+er) POV-Ray writes the full height into the image file header and only writes those lines into the image that are rendered. This can cause problems with image reading programs that are not checking the file while reading and just read over the end.

If POV-Ray wrote the actual height of the partial image into the image header there would be no way to continue the trace in a later run.

• Merged correction (writed->writes) back into main document. As well as missing caps on 1st words of last two paragraphs. BTW: It's not necessary to copy the ENTIRE page just the affected section(s) please. --jholsenback 03:30, 28 May 2010 (UTC)

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• Can someone check if there is still such system as MS-Dos for 3.7 ?

On MS-DOS with an eight character limit, myscene.pov would render to mysce001.tga through mysce100.tga. --Le Forgeron 22:05, 10 November 2010 (UTC)

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• Adding +STP/Frame_Step with #5183 (if/when merged)

Subsets of Animation Frames

Subset_Start_Frame=n	Set subset starting frame to n
Subset_Start_Frame=0.n	Set subset starting frame to n percent
Subset_End_Frame=n	Set subset ending frame to n
Subset_End_Frame=0.n	Set subset ending frame to n percent
Frame_Step=n	Set the increment to the frame number, default to 1
+SF0.n	Same as Subset_Start_Frame
+EF0.n	Same as Subset_End_Frame
+STPn	Same as Frame_Step

When creating a long animation, it may be handy to render only a portion of the animation to see what it looks like. Suppose you have 100 frames but only want to render frames 30 through 40. If you set Initial_Frame=30 and Final_Frame=40 then the clock would vary from 0.0 to 1.0 from frames 30 through 40 rather than 0.30 through 0.40 as it should. Therefore you should leave Initial_Frame=1 and Final_Frame=100 and use Subset_Start_Frame=30 and Subset_End_Frame=40 to selectively render part of the scene. POV-Ray will then properly compute the clock values.

Similarly, if you only want to render a tenth of the frames, you can use Frame_Step=10 to jump over the nine non-rendered frames between the rendered frames.

Usually you will specify the subset using the actual integer frame numbers however an alternate form of the subset commands takes a float value in the range 0.0 <=n.nnn <=1.0 which is interpreted as a fraction of the whole animation. For example, Subset_Start_Frame=0.333 and Subset_End_Frame=0.667 would render the middle 1/3rd of a sequence regardless of the number of frames.

--Le Forgeron 22:05, 10 November 2010 (UTC)