March 12, 2005

Ask the Guru: Cropping with an Aspect Ratio

Filed under: asktheguru — Tags: , — Eric Jeschke @ 10:49 pm

Cropping with an Aspect Ratio in the GIMP

First I just want to say again how glad I am to find this group. I have to say everyone here is extremely helpful and it’s very much appreciated. Being a user of Photoshop in the past, I really got used to a function for cropping…and I would like to know how to duplicate it in GIMP. Basically, when I would click on the crop tool in PS, a toolbar would show up and give you a list of various sized to crop the photo to, and when you dragged the crop tool over the image, you could make it crop where you wanted AND be the size you wanted. You could also set the dpi in this same toolbar.

I am sure I am just not understanding how to do this in GIMP, and would appreciate it if anyone would be so kind as to explain it. I am not a technical type at all, so all that stuff about x and y confuses me when I try to crop with GIMP. I have other questions, but I will save those for another time. Thank you again.

Lisa..who currently uses GIMP to edit digital photos of my 2 year old daughter =)

Hi Lisa,What you are talking about is setting a particular aspect ratio when you crop. This is done fairly straightforwardly in the GIMP, albeit perhaps not as simply as with the toolbar feature you describe. Here’s one way to do it…

Original photo. I’d like to make a 4×6 inch print (fairly standard print size at any US photofinisher) of a crop from it.

Choose the rectangular selection tool (keyboard: R) or ().If you want to crop to a certain print size (e.g. 4×6 in) or a certain aspect ratio (e.g. 2:3; same as 4×6) then in the Tool Options dialog, choose “Fixed aspect ratio” from the drop down dialog. Don’t choose “Fixed size” even if that is what you think you want.

In the Width and Height fields, enter the numbers for your desired aspect ratio. A 35mm film frame is 24mm x 36mm, so it has an aspect ratio of 2:3. This corresponds to common print sizes of 3.5 x 5 in (approx) and 4 x 6. An 8 x 10 print is related to the 4:5 aspect ratio of large format film, while 7×5 is closer to the 4:3 aspect ratio used by most digicams today.

You can set the units field appropriate for your numbers (e.g. in this case I set it to “in”, since I want a 4×6 inch print), although I don’t think it’s that important at this stage.

You do need to enter whole numbers, so round up to the nearest whole number aspect ratio.

Click and drag in the image window to marquee your selection. Zoom in a bit first if you like (as I did here). Don’t worry about getting the framing too precise, it is just a starting point. You should notice that the drag selection is constrained to your fixed aspect ratio. If you make a mistake just clear the selection (Shift+Ctrl+A) and drag again to make a different selection.Some handy keyboard shortcuts at this stage are:

  • +/-: zooms in and out
  • Ctrl + Shift + A: clear the current selection
  • Alt + Up/Down/Left/Right arrow: nudges the entire selection in the direction you are choosing
  • Alt + Shift + Up/Down/Left/Right arrow: bumps the entire selection in the direction you are choosing

Once the selection is approximately where you want it, choose the Crop tool (keyboard: Shift+C) or () and click on the image.

In the Crop & Resize Information dialog, click the “From Selection” button. The crop lines will be set to your selection made in the previous step. Now press Shift+Ctrl+A to clear the selection.Now you can fine tune the crop. Some handy keyboard shortcuts are:

  • +/-: zooms in and out
  • Alt + Up/Down/Left/Right arrow: nudges the entire crop in the direction you are choosing
  • Alt + Shift + Up/Down/Left/Right arrow: bumps the entire crop in the direction you are choosing

You can also use the mouse to enlarge or reduce the crop from any corner at this point, but be sure to hold down the SHIFT key or it won’t keep the aspect ratio.

Once you’ve got the crop lines positioned exactly as you want them, click the “Crop” button in the Crop dialog.

Don’t click Resize as this will only crop the pixels outside the crop lines but leave the canvas at the original size.

If you make a mistake, just Undo (Ctrl+Z) and try again.

Finally, set the print size (Image/Print Size) and set the width and height to the desired size. The dimensions should be compatible with your aspect ratio chosen in step 1 and you also probably want to make sure that the resolution (in PPI) is sufficient for a good, sharp print. In this case I chose to go with 3.5 x 5.25 which is the same 2:3 aspect ratio as 4 x 6. At 3.5 x 5.25 I’m getting close to 240 PPI which is quite sufficient for a very sharp print.

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