[wp-trac] [WordPress Trac] #53408: png images bit depth is modified in resized images
WordPress Trac
noreply at wordpress.org
Tue Jun 15 11:27:40 UTC 2021
#53408: png images bit depth is modified in resized images
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Reporter: wpfed | Owner: (none)
Type: defect (bug) | Status: new
Priority: normal | Milestone: Awaiting Review
Component: Media | Version: 5.7.2
Severity: normal | Keywords:
Focuses: |
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Hi,
When I upload a 8 bit png image graphic, WordPress resizes as usual but
modifies the bit depth to 24 or 32 bit, depending if their is a alpha
channel. Without Alpha channel it is 24bit, with it's 32bit.
The problem with that is that the file sizes end up being multiple times
bigger than the original image.
I opened a ticket with ImageMagick
https://github.com/ImageMagick/ImageMagick/discussions/3825
Some of the replies included these solutions:
**Setting bit-depth to 8 in the way done in the script may not be adequate
for PNG. I think the only way to ensure that is to preface the output name
with PNG8:filename.png. But I am not sure if it will preserve you
transparency if the input has transparency. But the best thing to resolve
that would be simply to try it.**
**Scaling the image, depending upon the scaling method, most likely will
add more colors than the 256 limit for 8-bit color. So the image has to be
forced to quantize colors to the 256 limit in order to save as 8-bits.
Otherwise, it is saved as 24 or 32-bits. So specifying PNG8:filename.png
will save as 8-bits.**
PNG00: Inherit PNG color and bit depth from input
image(https://legacy.imagemagick.org/Usage/formats/#png_formats)
Also here are related tickets I was able to find:
https://core.trac.wordpress.org/ticket/36477
https://core.trac.wordpress.org/ticket/30402
https://core.trac.wordpress.org/ticket/48736
Thanks!
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Ticket URL: <https://core.trac.wordpress.org/ticket/53408>
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