We have upgraded 2 days ago to 4.6.8 and since then we've noticed that some users are unable to upload images like they were used to.  I've had a look at our image settings and they are what they've always been

and if I try to upload a JPEG of 5000x3335, it resizes it just fine to the maximum (ratio) size and shows the preview

If I try a PNG of similar (4816 × 4784) size, it fails

 

I then tries resizing the PNG to smaller size and it fails at 3000x2000, but at 1500x1000 it works?!?

 

I can't seem to find what's going on here that causes those larger (dimensions, not filesize) PNG files to fail.  Anyone able to help?

 

Are you receiving a "-200" error or any further errors? Are you receiving any errors in your System Log? Are you using GD or Imagemagick? If any changes were made to your server, it is common that I see some hosting providers fail to install PNG delegates. That may be presented in the System Log for you to review.

GD is extremely resource hungry when resizing images and PNGs are rather large images. I would check your server error logs to see if you are running out of resources and for some reason it is simply not making it back as a "-200" error.

6 minutes ago, Westfield Sports Car Club said:

I can find no errors in the apache error log, except for a few times this one:

Allowed memory size of 134217728 bytes exhausted (tried to allocate 20480 bytes) in /home/forum/public_html/forum/system/Db/Select.php on line 498, referer: https://forum.wscc.co.uk/forum/

Note, this error only occurred 3 times today, and none assigned to my own IP address.  I however increased the memory_limit value in php.ini to 256M first, and now to 512M and with neither increased values has it mattered in regards to the uploading of my PNG test file.

 

I was hoping to see the GD error somewhere, but I've drawn a blank.

If you remove the resize settings in the ACP and upload the same file does it upload? If so, definitely something that would require more in depth review by yourself or your server administrator.

14 minutes ago, Westfield Sports Car Club said:

Set the image size to 5000 x 5000 and retried the file, but same result.

I'm the server administrator.

You'll want to set "Maximum image dimension to save" to Unlimited.