A new editing function added to Photoshop CS4 is Content Aware Scaling. It intelligently expands an image to fit a larger canvas size in much the same way an HD television expands a 4:3 standard definition show to fit a 16:9 HD screen.

In the example below I cropped the photo nearly square to eliminate a distraction on the left, but now I want to make a 10 x 8 inch print.

First I resized the photo to 8 inches high at 300 ppi, the resolution of the printer I planned to use for output. Next I expanded the canvas to 10 inches wide, putting the image in the center. From the Edit menu Contrast-Aware Scale was selected. Dragging the cursor down from the upper left corner I selected a section of the image on the left then pulled the left edge out to the edge of the canvas.

I repeated the select and expand process on the right side of the photo.

Resulting in the 3000 x 2400 pixel file needed to print an 10" x 8" file at 300 pixels-per-inch.