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Implement streamtype=1 option for tables-only JPEG encoding #7491

Merged
merged 1 commit into from
Nov 11, 2023
Merged

Implement streamtype=1 option for tables-only JPEG encoding #7491

merged 1 commit into from
Nov 11, 2023

Commits on Oct 25, 2023

  1. Implement streamtype=1 option for tables-only JPEG encoding 

    We already support streamtype=2 to skip producing JPEG tables, but
streamtype=1, which skips everything but the tables, was never implemented.
The streamtype=1 stub code dates to Git pre-history, so it's not
immediately clear why.  Implement the missing support.

jpeg_write_tables() can't resume after a full output buffer (it fails with
JERR_CANT_SUSPEND), so it might seem that Pillow needs to pre-compute the
necessary buffer size.  However, in the normal case of producing an
interchange stream, the tables are written via the same libjpeg codepath
during the first jpeg_write_scanlines() call, and table writes aren't
resumable there either.  Thus, any buffer large enough for the normal case
will also be large enough for a tables-only file.

The streamtype option isn't documented and this commit doesn't change that.
It does add a test though.

Co-authored-by: Andrew Murray <[email protected]>
    @bgilbert @radarhere
    bgilbert and radarhere committed Oct 25, 2023
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