As a result of the recent filewritetask investigation on the
S90 (thx to SticK) and
A810 (thx to nafraf), it looks like many of my previous assumptions were wrong.
It looks like that
- filewritetask only writes jpeg files (!), native raw is written elsewhere
- earlier cameras (including the S90) usually write the files in two chunks, first one is the exif part, second one is the main jpeg. On the A810 this is different, the whole file appears in one or two chunks, the exif is presumably embedded in the first chunk.
- another oddity on the A810: the chunks of the jpeg seem to come from non-contiguous buffers
edit:
... and of course there's no such thing as multiple filewritetask invocations for a single file, according to the collected data.edit, A810: Now it looks like that Canon has started doing some parallel processing. Sometimes, the jpeg file is starting to get written when only a part of the (L sized) compressed image is present. When an additional part of the image becomes available, it gets appended to the partial file on card!