Maintaining Aspect Ratio while Image Cropping using Preview

I like the convenience of being able to crop jpg/png images with Preview, but I would also like to be able occasionally to restrict the aspect ratio of the cropped image. This is useful, for instance, if I want to prepare images for printing in 4x6 or 5x7, while avoiding any surprise cropping made by the photo lab.

I am hoping there is a quick and easy way to do this (i.e., without needing to invoke the behemoth of image editing for this elementary task). Are you aware of one?

Solution 1:

In Photos (not iPhoto) click Edit

edit

then Crop

Crop

then Aspect, and finally Original

$Aspect\Original$ .

As of this writing (August 2016), there is no way to do this using Preview or any other stock program in El Capitan. Photos is nearly stock though, and it's easy enough using Photos.

Solution 2:

Do it in iPhoto.

Open a file.
Choose Edit.
Choose Crop or type c
Check constrain box for Original, the second dimension
Crop and hit Enter.
Save.

Solution 3:

There is no way to do exactly what you are specifying in Preview.app without doing a bit of math.

Holding down the shift key while using the select tool will force the select box to retain itself in square dimensions, while holding down the option key will open the select box from the center of where you begin your selection, while holding down both shift and option keys will implement both these features simultaneously. After creating the size of the select box that you want, you can use command-K to crop. Using the Adjust Size function in the Tools menu retains the aspect ratio by default.

Not what you asked for, but when using the select tool, you will notice numbers at 2 of the corners of the select box, and if you're very good with math (i.e. know if the numbers showing are multiples of your desired aspect ratio) and have a steady hand, you can accomplish what you are asking for on the fly. Otherwise, you'll have to figure out those dimensions beforehand or one at a time, and manually try to match up the numbers. In the end and in all circumstances, in my experience, mathematics is simply inescapable.

photo crop PRO

You may want to demo using an application dedicated to exactly what you want to do (rather than seeking functionality that just isn't there from such a simple, although often very useful, application such as Preview.app), for example, photo crop PRO. I personally would not recommend using Mac App Store ;-), but it is also available from the Mac App Store.

darktable

Alternatively, for an application far more powerful than either Preview or photo crop Pro, I've discovered darktable, which

"is an open source photography workflow application and RAW developer. A virtual lighttable and darkroom for photographers. It manages your digital negatives in a database, lets you view them through a zoomable lighttable and enables you to develop raw images and enhance them."

darktable can be installed manually, but is also maintained as a port using MacPorts, if you prefer to use package management. I've included step by step instructions for installing MacPorts and darktable below.

GIMP

Another extremely powerful alternative suggested in another response (I thank you Ecnerwal!) is using the GIMP. The GIMP can be installed manually, or built from source using MacPorts. I've included instructions below on how to install the GIMP using MacPorts. If you know Adobe Photoshop well, you may want to demo using GIMPshop, which very cleverly and conveniently reconstructs the look and feel of the GIMP to appear and behave nearly just like Photoshop... and its all for free.

MacPorts

If you're looking for a mature package management solution, for OS X I recommend MacPorts. MacPorts requires an appropriate version of xcode; xcode_5.1.1.dmg is the most recent version for Mavericks and Mountain Lion, and will require registering for free as an Apple Developer. Once registered and logged in, the link above for xcode will initiate the xcode download.

Get to know MacPorts

Install MacPorts

Enter these commands using /Applications/Utilities/Terminal.app

  curl -Ok https://distfiles.macports.org/MacPorts/MacPorts-2.2.1.tar.bz2

  tar xf MacPorts-2.2.1.tar.bz2

  cd MacPorts-2.2.1

  ./configure

  make

  sudo make install     # *not war!*

  cd ..

  rm -rf Macports-*

  sudo /opt/local/bin/port -v selfupdate

add MacPorts to your $PATH:

  export PATH=/opt/local/bin:/opt/local/sbin:$PATH

install darktable

  sudo port -vsc install darktable

install the GIMP

  sudo port -vsc install gimp

search MacPorts for other free photo utilities

  port search photo

to completely uninstall MacPorts

If, for whatever reason, you need to remove MacPorts:

  sudo port -dfp uninstall --follow-dependencies installed

  sudo port -dfp uninstall all

  sudo rm -rf /opt/local  

  sudo rm -rf /Library/Tcl/macports*