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Alternatively, you could set the interval to 300s and the renderer will update the image approximately every five minutes after it starts work on the frame. This time includes the renderer startup time, such as parsing RIB, cracking procedurals, and building ray tracing acceleration structures. As a result, there may be fewer increments before the first checkpoint than between later checkpoints. For convenience, the time-based interval can also be specified with a suffix suffixes of s, m, h, or d for seconds, minutes, hours, and days respectively and these may be combined. For example, intervals of 360s, 6m, 5m60s, and 0.1h are all equivalent. Instead of a suffix, you can also just specify a positive number and time in seconds will be assumed, while a negative number will be interpreted as the number of increments.


Note that checkpointing is designed for batch rendering to images on disk. Renders to a live framebuffer such as "it" are already updated on-the-fly as the render proceeds. Of the built-in display drivers, currently, only the TIFF and OpenEXR display drivers support checkpointing. You may notice that the files produced include a ~w labeled channel. This is data stored to resume a render from this file.

How to Specify

In RIB, checkpoints can be specified via an Option or by passing the optional -checkpoint argument to prman.

Code Block
prman -checkpoint t[,t]

The above command is seen as the interval given and an optional exit time (the square backets).

You can use several different types of intervals and may be combined:

  • 60s - this is 60 seconds
  • 60m - this is 60 minutes
  • 60h - this is 60 hours
  • 60d - this is 60 days
  • 60i - this is 60 increments (incremental frame rendering, this is ignored if you're rendering to tiles/buckets)

You can combine these as needed, for example: -checkpoint 1h30m would create a checkpoint every hour and 30 minutes

The options for exitat are the same and can even be provided without needed a checkpoint written, in which case you've just told the renderer you want to stop a render and write out the result at a certain time. Below we write out a final result and exit at 30 minutes

Code Block
prman -checkpoint ,30m

It is possible to maintain a checkpointed "final" image using either an .ini setting or a RIB option, with the later overriding the former. If neither is present it defaults to off. When set, this prevents removing the extra channels and the checkpoint tag when writing the final image for the render. The final image will essentially be just another checkpoint, rather than a slimmed down image. This means that once your image has reached the quality you've set and it completes, it can always be restarted by the user later: