"Bald Eagle" <cre### [at] netscapenet> wrote:
> The Continue_Trace option may not work if the Start_Row option has been set to
> anything but the top of the file, depending on the output format being used.
> Also POV-Ray cannot continue the file once it has been opened and saved again by
> any program.
>
> POV-Ray tries to figure out where to resume an interrupted trace by reading any
> previously generated data in the specified output file. All file formats contain
> the image size, so this will override any image size settings specified. Some
> file formats (namely TGA and PNG) also store information about where the file
> started (i. e. +SCn and +SRn options), alpha output +UA, and bit-depth +FNn,
> which will override these settings. It is up to the user to make sure that all
> other options are set the same as the original render.

This section in the docs is outdated and not valid for 3.7. The partial image
writing was buggy and not compatible with parallel block-based rendering. In 3.7
the image file isn't written partially. Instead, an intermediate file is used to
hold all rendered blocks and POV-Ray is able to figure out which blocks are
missing and render all those. It doesn't parse any image file format header,
which, btw, are not what you think they are anyway.

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