I have a bunch of png images that I'm editing to add rounded corners on my mac, to do this I'm going through the length process of:-

Opening a file Adding an alpha channel Selecting a rounded rectangle Inverting the selection Cutting out the selected area (leaving a rectangular image with rounded corners) Overwriting the file

I've noticed that on some images however the saved file doesn't show the rounded corners, some do and some don't but from what I can see there's no pattern why some pick up the updates and others don't.

The images are definitely updating as they show a new last updated date timestamp, and if I save them as another image file it still creates them without the rounded edges. The only way I've found around this is to cut the image out, paste as a new image and then save that as a new file, delete the old one and rename, which is a major PITA.

Any suggestions very welcome! Cheers!

  • You can perhaps do it with a script file and Imagemagick, see first post
    – xenoid
    Commented Feb 29, 2020 at 9:43
  • @xenoid cheers I'll check that out!
    – MorkPork
    Commented Mar 2, 2020 at 11:13

1 Answer 1


I've managed to work out it, some images had their mode set to indexed, this wouldn't save properly, all I had to do was change the mode to rgb (as some were) and then it saved fine. Now to work out how to bulk update all the images to have a mode of rgb! 😓

  • You should still have gotten something, but likely with some pixelation. Can you attach example files? Commented Feb 29, 2020 at 3:51
  • AFAIK indexed images are either GIF (always) or PNG (quite rare). There are command-line-utilties to determine this. On Linux (and likely OSX) the file {file} command prints information about any file you throw at it, look for colormap. ImageMagick's identify tool uses '256c' for same.
    – xenoid
    Commented Feb 29, 2020 at 9:42
  • @MichaelSchumacher there was nothing that I could see different between the before and after but I've worked it now thanks 😊
    – MorkPork
    Commented Mar 2, 2020 at 11:11
  • @xenoid I can't attest the norms but I can see after checking that a very large chunk of the files I have, that are all pngs, have been set to indexed for whatever reason, which is a bit of a headache!
    – MorkPork
    Commented Mar 2, 2020 at 11:12
  • 1
    have been set to indexed for whatever reason: usually that makes them smaller... They could have been processed by PNGCrunch or similar.
    – xenoid
    Commented Mar 2, 2020 at 12:23

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