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[Solved] Lossless JPG cropping

Posted: Fri Jan 11, 2019 7:28 pm
by AnalogRelic
Setting up a new Mac from scratch (rather than from a backup' so new settings) and when I try to do a lossless .jpg crop, it brings up a dialog box saying ' jpg cropping isn't supported by many apps' and strongly suggests me to use .tiff instead. It worked just fine on my old Mac. I know it's a setting somewhere but don't remember where. Anybody?

Re: Lossless JPG cropping

Posted: Sat Jan 12, 2019 4:26 pm
by forum_adm
Please e-mail a screenshot of the dialog.

Did you maybe select the lossless codec?

Just go to the prefs part open/formats/jpeg and select JPEG6 as open library.
Open your file.
Crop lossless.
Save as.

Thorsten

Re: Lossless JPG cropping

Posted: Mon Jan 14, 2019 3:44 pm
by AnalogRelic
I might have.

Found the menu you referenced and didn't see anything about 'JPEG6' or 'libraries', but I did hit the 'restore defaults' button as an experiment and it seems to have worked this time on my test image.

Thanks for the help. GC is a unique and under-appreciated app in my view. Oh, one additional question: Are jpg rotations in GC lossless also?

Re: Lossless JPG cropping

Posted: Mon Jan 14, 2019 4:14 pm
by AnalogRelic
OK. Not sure what I'm doing wrong here. Attached is a screenshot of what I get when I choose the 'Save As' dialog. It saves an image which won't open. The dialog is different from the way it worked on my old computer, but I did a clean install so the settings didn't transfer. On my old installation, it just had a 'lossless' button without the warning when you opened up 'options'. To repeat, there is no 'jpeg6' listed under 'formats' and I can't find anything mentioning libraries.
Screen Shot 2019-01-14 at 10.05.37 AM.png
Screen Shot 2019-01-14 at 10.05.37 AM.png (241.05 KiB) Viewed 7013 times

Re: Lossless JPG cropping

Posted: Mon Jan 14, 2019 4:18 pm
by AnalogRelic
Screenshot of Formats pref list
Screen Shot 2019-01-14 at 10.16.32 AM.png
Screen Shot 2019-01-14 at 10.16.32 AM.png (218.23 KiB) Viewed 7013 times

Re: Lossless JPG cropping

Posted: Tue Jan 15, 2019 8:42 am
by forum_adm
The lossless JPEG codec is only for usage in special medical apps.
Regular apps will not be able to open JPEGs compressed with the lossless codec.
Please use baseline in general.

I made a short tutorial movie about the lossless JPEG cropping:
https://www.lemkesoft.info/forum_movies/lossless.mp4

Thorsten

Re: Lossless JPG cropping

Posted: Tue Jan 15, 2019 8:44 am
by forum_adm
The JPEG rotation is lossless if you rotate from the browser (toolbar or context menu):
Screen Shot 2019-01-15 at 08.44.07.jpg
Screen Shot 2019-01-15 at 08.44.07.jpg (176.18 KiB) Viewed 7009 times

Re: Lossless JPG cropping

Posted: Tue Jan 15, 2019 3:33 pm
by AnalogRelic
A-HA!!! That's IT!!! Took me a moment to find the tool grid (maybe it could be added to the View menu; the only way I was able to bring it up was from the little 'wrench' icon in the image window.) Maybe this could be in the Preferences too, as that seems like basically what it is.

Thanks for the tip about the lossless jpg rotation in the browser. Sounds like this is different behavior than what happens when you select Picture>Rotate from the toolbar with an image open. Seems like it should do the same thing there though; why would one want lossy rotation if lossless is possible?

Your video was just what I needed. It had been so long since I had dug into those settings (and I think it it was in a different place the last time I did it).

Thanks for the help!

Re: [Solved] Lossless JPG cropping

Posted: Tue May 17, 2022 9:00 pm
by Knocks
Hi, found this thread via Google.

I think there is confusion here because in most contexts, "lossless JPEG cropping" does not mean saving to some fancy "lossless JPEG" format (I didn't even know such format existed). To most people, it means cropping a JPEG (which is already lossy by design) without re-compression. The JPEG specification allows that, as long as you crop along pre-defined block borders, which means your cropped selection may not always align perfectly to what's possible to crop losslessly. To bypass that limitation, most software will simply crop a slightly larger selection to conform to existing blocks. It's still better than going through lossy compression multiple times.

In Windows, I used IrfanView with a lossless JPEG crop/rotate plugin for this purpose. I have not found Mac software that does the same thing yet.

Re: [Solved] Lossless JPG cropping

Posted: Wed May 18, 2022 9:40 am
by forum_adm
GraphicConverter supports the lossless cropping of JPEGs.

Just double click onto the selection tool after opening a JPEG and enable the lossless cropping.
Make the selection.
Select File/Save as
Save as JPEG

That's it.