Problems with transparency in png images using 2.61

Hi all,

Hope someone will comment on this soon.

Thanks,

Jerry Kornbluth

Hey, Jerry.

I set up a similar test with version 2.61 and see the same results you do. I tested on the same server with version 1.27 and didn't have a problem.

I changed the following image quality setting and the transparency was fine at any size thumbnail.

FILE: /lib/image_functions.php (approx line 63 & 64)

// resample image
$quality = 4; // v2.60 Speed up resizing (was 5 previously)

Here I changed: $quality = 4;     To: $quality = 5;

I can't say what impact the quality difference would have on a site when uploading or batch resizing a large quantity of images, but maybe upgrading the GD library on my server would accomplish this task with the lower quality setting. I didn't have time to look into that further, but maybe this will get you where you need to be today.

Hope that helps.

~ Deborah

Hi Deborah,

Thanks for the heads up, I'll give it a try and report back.

BTW, how did you discover the fix?

Jerry Kornbluth

Jerry, I did a some online sleuthing and as a result of viewing posts from multiple sites, deducted that the image quality during resizing was a possibility. There must have been a valid reason for Interactive Tools to reduce the image quality in the 2.61 script. Maybe for some servers a faster processing speed is necessary.

~ Deborah

Hi All, 

That is some amazing sleuthing, thanks!  

The adjustments to the image quality were to allow resizing/resampling of very large images that would otherwise be to slow or require too much memory.  How it works is we do a fast resizing of large images to something more manageable, then a smarter resampling down to the desired size.  Usually it doesn't look much different, but it looks like we're losing the transparency on the pngs.  

We'll do some research on this and post a patch/fix.

Stay tuned.

Thanks Dave.

I'll be on the lookout for your fix..

Jerry Kornbluth

Hi All, 

Here's a patched /cmsb/lib/image_functions.php (attached).  Can you try making a backup of your current image_functions.php and replacing it with this one?

I've added the code to maintain transparencies to the fast image resizing code, so you should be able to get the benefits of both now.

Let me know if this works for you.

Dave, the patch works for my tests. All sizes of pngs have retained their transparency.

Thanks!
Deborah