How to you crop pictures in Preview without changing quality

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Level 1

15 points

How to you crop pictures in Preview without changing quality

I really miss MS Office Picture manager. It was great for simple, quick edits, cropping, batch resizing, etc, and didn't try to take over your pictures like everything else seems to. I don't want to use iPhoto (I won't go into that here) or Picassa so I have been using Preview to crop photos. I just noticed that is is doing more than just cropping though. It is changing the quality. I verified this by "cropping" a picture at the original size, and then when I exited the picture, the file size was reduced by about a third, and when viewed again, the quality was noticably reduced. There is no setting in "Preferences" that addresses this. I can't find any way to control it. Anyone?

Posted on May 12, 2013 2:05 AM

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Answer 1

Paul_31

Level 6

14,172 points

May 12, 2013 2:29 AM in response to IPatronius

I'm not seeing the same results. I just experimented with a few pictures. I used some decent quality images to start with, and in Preview cropped them (selected the area, Command+k to crop) and exported the cropped version and retained the original for comparison.

Certainly, cropping reduced the file size, but that's to be expected as I've deleted pixel data. I then examined the originals alongside the cropped versions, enlarged them on screen and cannot discern any quality loss 😕.

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Answer 2

IPatronius Author

Level 1

15 points

May 12, 2013 3:31 AM in response to Paul_31

Yes, the difference is you're exporting. You can control the image quality then. That is certainly an option but if I am cropping 100 pictures, having to "export" every one takes significantly more time, (especially since you would then have to go back and "undo" the crops on the originals if you don't want to lose the quality). Try it again by copying the original, then just cropping to original size and then saving it (exit the picture).

I think it also makes a difference what jpg quality you start with. What I think is happening is that Preview is saving at a pre-determined quality level, say 70%. So if you started with a picture that was at 70%, if you you crop it, it may not make a difference. But if you start with a picture that was saved or created at 85%, and then when you crop it Preview saves it at 70% (without asking you of course since Mac always knows best) then you have the quality loss. What it should do, in my opinion, is always save it at whatever quality level the original is at, unless you tell it otherwise.

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Answer 3

Paul_31

Level 6

14,172 points

May 12, 2013 3:30 AM in response to IPatronius

Still not seeing it with just cropping and saving - not exporting. I've zoomed in in Preview and they look the same. I then viewed them in Pixelmator and they looked the same, but oddly none of them look as good as they do in iPhoto (I know you don't want to go there).

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Answer 4

LenTS

Level 1

0 points

May 14, 2013 12:34 PM in response to IPatronius

I learnt the hard way pretty early on in my photo editing days that if I was picky about quality, I should shoot in RAW and only convert to a compressed format after doing most of my edits. If I am doing a lot of edits, I import the images into a pro photo editor and process there. Since you can batch process there you can do most things efficiently.

As for Preview, I've only used it to crop images that are already not that great, like scanned CD covers, and those are not made noticably worse by cropping. But I never edit in place - I always output the changes into a new file or have a list of edit commands (as in Aperture). So can't help with in-place edits in Preview.

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Answer 5

IPatronius Author

Level 1

15 points

May 12, 2013 3:32 AM in response to Paul_31

I was editing my reply while you were responding....

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Answer 6

IPatronius Author

Level 1

15 points

May 13, 2013 10:34 AM in response to IPatronius

I guess no one else has experienced this?

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