Sometime you just want to tweak an image and move on... fast. At that moment, you don't want commitment (iPhoto, Aperture, and Lightroom), or a bizillion editing options (Photoshop), you just want to brighten the picture, adjust the color, crop it, and be done.
We have great news for you. This application exists, it's free, and it's already on your Mac. It's called Preview.
Many Mac users prefer using Preview for working with PDFs because of its clean interface and no-nonsense set of tools. What may surprise you, however, is that this application also has a robust set of imaging tools.
I'm not just talking about double-clicking on a photo and looking at it on your computer. Beyond that, you can adjust an image's tonality, color, and even select objects within the shot to copy and add to other photographs. To prove my point, I'm going to take you on a quick photographer's tour of this handy imaging application.
Customize the interface
A good way to get a feel for the functions available in Preview is to customize the top toolbar. Go to View -> Customize Toolbar, and you'll see icons for zooming, selecting, cropping, rotating, and even scaling. Drag the tools you will use the most often to the top toolbar so they're ready when you need them.
Next, go to Preferences (Preview -> Preferences), click on the General tab, and click on the radio button next to "Open groups of files in the same window." This allows you to work on multiple images at once in Preview.
Test this by selecting a handful of pictures and dropping them on the Preview icon. You'll get a column of thumbnails displayed in the sidebar with one image featured in the main window. You can navigate the thumbnails by clicking on them individually, or by using the up and down arrow keys. If you want to add another picture to the line up, just drag it to the sidebar and let go.
Right-click or Control-click in the sidebar and you'll be presented with options for sorting the thumbnails or choosing how many columns you want them displayed in. If you don't like the default sorting options, choose None from the contextual menu and you can drag the thumbnails in any order you want.
Batch processing
You can also perform basic batch processing on multiple images with Preview. Command-click on two or more thumbnails in the sidebar, then apply the rotate command. You'll probably want to use the Rotate button in your top toolbar, but if it isn't there, then go to Tools -> Rotate Left or Rotate Right. The rotation will be applied to all of the selected images in the sidebar.
Bonus tip! If you do use the Rotate button, you can reverse its direction on the fly by holding down the Option button.
Maybe your images are too big and you want to sample them down. Command-click on the thumbnails of the images you want to resample, then go to Tools -> Adjust Size, and choose the new dimensions that you want to use for the photos. Preview will resample all selected images. How's that for efficiency?
Tonal and color adjustments