In this tutorial I will show how to use Gimp to crop to a specific size and aspect ratio. I'll be using the macro image I snapped on a recent camp-out. You can use any photo you would like.
1-Understanding aspect ratios
It is important to know that all photo development labs, weather at Wal-mart, Walgreens or Kmart, develop and print photos at specific standard sizes that are are more or less universal. These various sizes come in two different aspect ratios. The reason for this, I believe has to do with the various types of cameras in use by the general public. Respectively, most cameras (Medium and large format are excluded from this) shoot in two aspect ratios. One is wide and the other not so wide. Below are shown the two aspect ratios and their respective sizes within those ratios.
2-Crop to a specific aspect ratio in Gimp
Activate your crop tool. Then simply click on the 'fixed' icon in the crop tool palette as ssen below. Once this is done your crop will be to the exact aspect ratio of whatever image you have open. But what if your image was shot at a 5x7 ratio, and you want to crop it to a ratio that will allow you to print it at a 4x6 or 8x12 so you dont have to worry about the photo lab cropping out parts of the photo you want to remain. Read on to find out.
3-Changing the aspect ratio of your photo
There are several ways to do this, but I find this way the simplest. first, in the menus, go to 'image'> 'Scale image'. In the dialogue that opens change the 'pixels' to 'inches'. In my case I want this image to be 6 inches tall at 300 DPI. If you want yours to be 8x12 Just change the 'height' to 12. Below is what I did.
4-Crop to the correct size
Create a crop frame on your image, it doesn't matter what size. Now in the crop palette change the size parameters to 'inches' and the crop-box size to 4x6. Then reposition the crop-box to what ever position you desire. After this type return to make the crop permanent. See below for the crop palette settings.
I hope this is understandable. Keep in mind that you can crop from a 4x6 aspect to a 5x7 by changing the 'width' instead of the height in the 'Scale image' dialogue. Enjoy cropping!