Implement streamtype=1 option for tables-only JPEG encoding
#7491
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
bgilbert
force-pushed
the
jpeg-tables-only
branch
from
e8ebc48 to
2a5eac0
Compare
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
force-pushed
the
jpeg-tables-only
branch
from
2a5eac0 to
4d7372b
Compare
Contributor
Author
|
Updated based on suggestions in bgilbert#1. |
radarhere
approved these changes
Oct 31, 2023
radarhere
added a commit
to radarhere/Pillow
that referenced
this pull request
Dec 8, 2023
radarhere
added a commit
to radarhere/Pillow
that referenced
this pull request
Dec 8, 2023
Merged
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
We already support
streamtype=2to skip producing JPEG tables, butstreamtype=1, which skips everything but the tables, was never implemented. Thestreamtype=1stub 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 withJERR_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 firstjpeg_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.I've opted to implement the early exit with a
gotorather than refactoring the state machine. If thegotois not desired, it would be possible to add a dedicated cleanup state, do an early return after writing tables, and require a second call into the state machine to finish cleanup.The
streamtypeoption isn't documented and this PR doesn't change that. It does add a test though.