This installment in my GIMP Beginners series is about Rotating and Cropping images (just as the title suggests). The areas covered being basic orientation (portrait vs’ landscape), straightening horizons, corrective cropping (after leveling of horizons) and cropping to a specific ratio. This tutorial is based on GIMP version 2.6.2.
Basic Orientation (portrait vs’ landscape)
So you’ve just opened your image in GIMP but you find yourself placing your head on one shoulder to see it right. There is luckily a one step fix for this problem.
1. From the dropdown menus select Image > Transform and then select Rotate 90 clockwise or counter-clockwise as appropriate.
Tip: Rotating a .JPG image in this fashion will cause some deterioration in quality. If you are editing an image for use on the internet you will need to rotate it, however if you are editing a file for printing you may wish to simply skip this step and perform your edits in the default orientation, your printer will not know any differently.
Now check to see that the camera was level when the shot was taken, the best check for this is the horizon. If your horizon sloping to one side or all your buildings are leaning to the left or right proceed as follows.
1. Move you mouse to an area roughly in the center of the horizon and note the coordinate given at the lower left corner of the image window.
2. From the dropdown menus select Image > Guides > New Guide…
3. In the resulting ‘Script-Fu New Guide’ dialog box select Horizontal from the dropdown box and enter the number which we memorised in step 1, then click OK. (If you are using a building to test the straightness you will select Vertical from the dropdown and enter the number from the left rather than the right).
4. From the Toolbox select the Rotate tool and mouse click anywhere in your image.
5. In the ‘Rotate’ dialog box change the Angle until the horizon runs parallel to our guide, click OK when you are done.
6. Now turn off your guides by selecting Image > Guides > Remove all Guides.
Tip: If you are using a building it is best to select one from near the center of the photo. This is due to the fact that some camera lens (wideangle) may cause buildings to slope inwards as they rise, this is called “converging verticals”, I have a feeling that we’ll be coming back to this is a later installment.
If you have rotated your image in order to straighten it corrective cropping will your next step. To do this
1. From the Toolbox select the Crop tool. To keep the cropped image the same basic shape as the original make sure to select Fixed for ‘Aspect Ratio’ in the tool options.
2. Using your mouse, click and drag to roughly the size you wish to crop, you can now fine tune the crop area by using the mouse to drag the sides of the area to their final positions. When you are happy go back to the ‘Crop’ dialog box and click OK.
There will of course be time when you wish to use cropping to change the basic shape of your image, for instance to fit an 8 x 10 photo frame. To do this
1. From the Toolbox select the Crop tool.
2. Make sure that Fixed is selected for ‘Aspect Ratio’ in the tool options and now use your keyboard to enter “8:10” in the box. You can use the Portrait and Landscape buttons to flip the crop area if needed.
3. Using your mouse, click and drag to roughly the size you wish to crop, you can now fine tune the crop area by using the mouse to drag the sides of the area to their final positions. When you are happy go back to the ‘Crop’ dialog box and click OK.