[Solved] reset alpha channel setting

[tomj72]

I have 2 macs both using 11.5.5. I've used QGIS 3.12 to make and download maps in PNG format. The PNG have transparent backgrounds. One mac opens the files with transparent backgrounds. The 2nd mac opens with white backgrounds. I probably screwed up when asked about the "alpha" channel setting up the 2nd mac. Any suggestions on how to undo or otherwise fix my problem. I've been using the 1st mac (or it's predecessors) in this way successfully for nearly 10 years and I've forgotten what I did originally. Thanks, Tom

[forum_adm]

Just go to the prefs:

Screen Shot 2022-01-12 at 07.02.jpg (253.85 KiB) Viewed 918 times

[tomj72]

Unfortunately that's exactly how I have set my 2nd mac (the one that doesn't display transparent parts as checkerboard). As an experiment I tried opening the file on both computers in Adobe Photoshop Elements 2020 and the same thing happens: mac 1 shows checkerboard, mac 2 white. I guess it isn't a GraphicConverter issue. Thanks for the reply.

[tomj72]

Apparently I'm omissing something very simple but not easy to find. In Adobe Photoshop Elements to set up a checkerboard for transparency you are given 2 colors to select for the checkerboard. Using this the checkerboard pattern shows up nicely in the transparent parts of the png file. In GIMP, the checkoard pattern shows up properly by default. I can't find an option like this in GraphicConverter. The only thing I can find about the checkerboard pattern is the option General:Display Content:Editing Alpha Channel which has 2 options black or white; neither of which seems to have any effect on the transparent part of the png file. Sorry for being so dense.

[forum_adm]

GraphicConverter displays here the checkerboard for transparent parts:

Screen Shot 2022-01-13 at 06.58.40.jpg (193.52 KiB) Viewed 904 times

The screenshot shows the default behavior.

Maybe the prefs are corrupted. What happens if you trash them with our First Aid?
https://www.lemkesoft.info/files/graphi ... st_aid.dmg

Please email a sample file which does not work to support@lemkesoft.com

[tomj72]

I just relooked at your Jan 13, 2022 1:59 am reply and realized on my macbook pro Safari didn't show the checkerboard on your display example. I just opened your reply in Safari on my mac mini, and it does show the checkerboard pattern in your example. As far as I can tell both of my computers have the exact same versions of mac OS and Safari.

[forum_adm]

So, that must be a local issue onto your system.

[tomj72]

Sorry if this is a repeat, I may have sent it before I was finished.
Found it! It was a setting in the Display part of the Accessibility portion of System Preferences. It turns out increasing the contrast can also wash out the white/grey checkerboard used to display transparency in the alpha channel. Reducing transparency has a similar but some what more logical effect. Thanks to Google and a hint by OWC: https://eshop.macsales.com/blog/78374-h ... -in-macos/.