How to Modify Your Images

Image Manipulation Programs from simple to more complex

On your MacBook Pro, you’ll find two programs that more or less obviously deal with photo manipulation: iPhoto and Gimp. As its name suggests, iPhoto is made for tweaking your photographs. Gimp’s great for more powerful image manipulations—it is very much an open-source Adobe Photoshop. However, you may not realize that Preview, which is most often used to view PDF documents, also handles a low level of image manipulation, making it the perfect tool to use when you quickly need to make your image web-ready. In this post, I’ll be discussing how to make all these easy adjustments—namely, rotating, cropping, and retouching— in Preview.

1. Rotating
In Preview, all of the image manipulation you need can be found in the Tools menu. Preview allows you to rotate images in four directions very simply—left by 90 degrees (counterclockwise), right by 90 degrees (clockwise), horizontally (mirror image), and vertically (upside down image). As you can see from the screencapture at right where I’ve highlighted these menu options, you can also rotate left and right using key shortcuts (command-L and command-R, respectively).

2. Cropping
As you may notice in the screencapture in the section above, the Crop option is grayed out in the Tools menu, meaning that it is currently unavailable to use. To activate the Crop tool, you must select an area to be cropped. When you open a file in Preview, you are given a small set of tools directly on the top of the image panel, as seen in the screencapture at right. The dotted box is the selection tool that will allow to select what parts of the image you want to save and what parts you want to crop out. To perform this operation, you click the tool, then click and draw a rectangle in the image that selects the area you want to save. (Note, there are other shapes and ways you can use to crop your images in Preview, but the default rectangle shape will probably be what you use most of the time.) You can readjust the rectangle after you’ve initially drawn it, to modify what it is you’ll be cropping out (i.e. the unselected bits). Once you’re satisfied with the area you’ve selected, click the Crop option in the Tools menu or use the keyboard shortcut, command-K.

3. Retouching
To retouch your images, you select Adjust Color, highlighted in the Tools menu in the screencapture at right. Once you click that, another panel will appear (as seen in the next screencapture). This panel allows you perform a lot of different things that can radically adjust your image. I’ll quickly detail a few here that might be of use to you:
Exposure & Contrast—Both of these tools will allow you to adjust the colors in your image to make them lighter or darker.
Saturation—This tool can increase or decrease how vivid or intense the colors in your image are. If you want to easily convert your image to black and white, you can drag the saturation all the way to the left and dispose of the colors completely.
Temperature—Dragging this tool to the right will ‘warm’ up your colors (increasing the yellowish tone of your image), while dragging this tool to the left will ‘cool’ your colors down (giving your image a bluish cast).
Sepia—Dragging this tool to the right will increase the brownish cast of the image. If you drag the tool completely to the right, you will have a fully sepia-toned image.
Sharpness—Dragging this tool to the left will make your image more blurry, while the rightward direction will sharpen it up.

4. Saving Your Image
In OS X Lion, the way you save your file has changed, and the terminology may be a little confusing to you. Under the File menu, you’ll see Save a Version, which is synonymous with Save, meaning that clicking this option will save your changes over your existing file. You will also see Export, which is synonymous with Save As, meaning that you can save your edited file under a new name and can also change the file extension if you’d like. On that note, most images you create for the web, you’ll want to save as a JPEG. For more information on how to save files in OS X Lion, check out this document.

5. Extra Credit
Check out these posts written by fellow ITFs about how to do even more with your images:
How to Resize Photos (gives directions for both Preview and iPhoto)
Creating a Slideshow (using the NextGEN Gallery plugin—to use this feature on your blog, select Plugins from the options along the left-side of your Dashboard, find NextGEN Gallery in the alphabetized list, and click “Activate.”)

6. Need More Help?
As always, you should feel free to send me an email. However, your issue may be something that other students are experiencing, so you should also feel free to comment here about any image modification frustrations, and I can answer you in the comment train or in a new post.