iphoto

iPhoto makes editing fast and easy. But more importantly, it's non-destructive. iPhoto keeps track of edits done in a folder or smart folder and applies them on export while keeping the original photo untouched. This means you can make adjustments without having to save multiple copies.

We'll examine the major tools that you need. Start by importing the images in the Editing folder. When you're done click Last Import in the Source List.

Straighten

Sometimes things get a little out of whack. If you lean to the side when you take a photo, a horizon line or building collumn may tilt to the right or left. Double-click on the image named Straighten.jpg and click on the Edit button in the bottom toolbar.  By default, the Quick Fixes tab is showing. Click on the Straighten button to activate the tool.

A yellow grid will appear over your photo as the tool appears. Drag the slider to adjust the horizon to match the grid (about three degrees). Notice that you have the option to revert to original. When you're finished click Done. 

The Rotate button is a little different. Clicking it will rotate an image 90 degrees. 

Adjusting color

There are two ways to adjust color in iPhoto. The first is to use the Enhance feature. It automatically adjusts the photo based on color, exposure and several other settings. Click Last Import in the Source List and double-click AdjustColor1.jpg. Make sure the Edit panel is open and click the Enhance button. You should see something that looks like this.

Not bad for an auto-adjustment.

But there are many cases where this works poorly or not at all.  Click on Last Import and then double-click on Color-Adjustment2.jpg. This time when you click Enhance, the photo doesn't get much better. When this is the case, click Revert to Original at the bottom of the Edit panel and click the Adjust tab at the top of the panel.

Generally, when adjusting a photo you want the colors (represented by the graph) to be distributed across the entire range. That's not the case in this photo. You can fix it by dragging the white and black sliders to the edge of the graph and move the midtones slider to the left until it looks like this.

If you do nothing else, this will help you improve the quality of your photos. Play with the other settings but be careful. It's easy to go too far.

Cropping

Click on the Quick Fixes tab and click the Crop button.

Unlike a lot of free photo editing software, iPhoto lets you set a custom size and crop to fit. Select Custom... from the dropdown menu.

Change the size to 620 x 450 and check the constrain box. Notice that the bounding box (crop area) on the top of the photo changes size.

Now when you click and drag the the corner of the bound box it will change to meet that shape. It also gives you a grid to check your composition. 

Click Done to make the crop take effect and resize the photo at the same time.