Skip to content

Allow fewer PNG palette entries than the bit depth maximum when saving#5330

Merged
hugovk merged 1 commit intopython-pillow:masterfrom
radarhere:png_plte
Mar 21, 2021
Merged

Allow fewer PNG palette entries than the bit depth maximum when saving#5330
hugovk merged 1 commit intopython-pillow:masterfrom
radarhere:png_plte

Conversation

@radarhere
Copy link
Copy Markdown
Member

@radarhere radarhere commented Mar 15, 2021

Resolves #2202

Currently when saving a PNG in P mode, Pillow sets the number of bytes in the palette at two to the power of the bit depth, times 3 for the colors.

Pillow/src/PIL/PngImagePlugin.py

Lines 1272 to 1274 in 8064e04

if im.mode == "P":
palette_byte_number = (2 ** bits) * 3
palette_bytes = im.im.getpalette("RGB")[:palette_byte_number]

As pointed out in the issue, https://www.w3.org/TR/PNG/#11PLTE states that

It is permissible to have fewer entries than the bit depth would allow.

So this PR changes palette_byte_number to the number of colors times 3 instead.

The length of the tRNS chunk is also changed, as https://www.w3.org/TR/PNG/#11tRNS

The tRNS chunk shall not contain more alpha values than there are palette entries

This was referenced Mar 15, 2021
Closed
Closed
@hugovk hugovk merged commit ddcc936 into python-pillow:master Mar 21, 2021
@radarhere radarhere deleted the png_plte branch March 21, 2021 19:46
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Reviewers

No reviews

Assignees

No one assigned

Labels

None yet

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

PNG: unnecessary padding in PLTE

2 participants

@radarhere @hugovk