Trimming Pictures to Standard Photo Sizes

Use Photoshop Elements' Crop tool to quickly crop a digital photo so that it fits into a standard-sized frame. Find out why automatic cropping tools sometimes don't leave you with the best image, and how to do it better by hand.

Some photo editors enable you to constrain the Crop tool to drawing a crop boundary that has a specific aspect ratio. You may even be able to use the tool to establish both the image print size and output resolution simply by cropping.

These features may seem like the perfect way to adjust your picture so that it fits a certain picture frame. Unfortunately, using these crop options can leave you with fewer pixels than you need to produce a suitable print. In some cases, the program may add or delete pixels automatically in the course of applying the crop, and that's a job that you, and not some automatic software control, should handle.

The following steps show you a safer way to achieve a specific output size in Photoshop Elements. This technique involves drawing a selection outline with the Rectangular Marquee tool and then applying the Crop command. (You can use the same steps in any program that offers similar features.)

1. Save a backup copy of your original image.

2. Grab the Rectangular Marquee tool, labeled in Figure 1.

3. On the Options bar, set the Style option to Fixed Size, as shown in the figure.

4. Figure out how many pixels you need for your final output.

You calculate these numbers differently depending on whether you want to print your picture or use it on-screen:

• For print output: Multiply your desired output size by the optimal output resolution your printer needs. For example, if your printer manual says that the printer does its best work when an image has an output resolution of 300 ppi (pixels per inch), and you want a final print size of 4 inches wide by 6 inches tall, you need 1200 pixels horizontally and 1800 pixels vertically.

• For screen display: Match the pixel count to the amount of screen real-estate you want the picture to consume. Remember that a monitor uses one screen pixel to display each image pixel. So on a monitor set to a screen resolution of 800 x 600, an image that's 800 pixels wide by 600 pixels tall fills the screen.

If you want to use your picture both ways, crop with the print requirements in mind. Then make a copy of the image for use on-screen and eliminate excess pixels to get the screen display size you need.

5. Enter the pixel values you calculated in Step 4 in the Width and Height boxes on the Options bar.

Elements assumes that you want to use the same unit of measurement as the rulers that appear alongside the image window. If you don't see the rulers, choose View --> Show Rulers or press Ctrl+R (Command+R). You establish this measurement unit by choosing Edit --> Preferences --> Units & Rulers and selecting an option from the Rulers menu in the resulting dialog box.

If the rulers aren't set to pixels, be sure to type the letters px after the value that you enter in the Width and Height boxes. For example, to set the width to 600 pixels, type 600 px. Press Enter after you enter the value.

6. Click in the image window.

A selection outline appears, as shown in Figure 1. The dimensions of the outline match those you set in the Width and Height boxes.

7. Move the selection outline to frame the portion of the picture you want to keep.

To move the outline, drag inside it. You also can nudge the outline by pressing the arrow keys. Press a key once to move the outline one pixel; press Shift plus an arrow key to move the outline 10 pixels.

8. Choose Image --> Crop.

9. If you're printing the photo, establish the output dimensions.

At this point, you've established the number of horizontal and vertical pixels, which is the end of the line if you're preparing a photo for on-screen use. But if you're printing the picture, you still need to specify the final output resolution (pixels per inch) and print size.

In some cases, the selection outline that you create in Step 6 may be smaller or larger than the portion of the picture you want to retain. In Figure 1, for example, the outline includes too much of the background at the top of the picture. What to do? The answer depends on the way you plan to use the photo and whether you want to cut away less of your picture or crop the image more tightly.

• To retain more of the photo: If you enlarge the selection outline to retain more of the picture, you will wind up with more pixels than you need (because you capture more pixels than your original formula suggested). That means that you can crop to any size — as long as it's larger than your original outline — without worry.

To make your life easier, press Ctrl+D (Command+D) to get rid of the existing selection outline. Then abandon the Fixed Size tool setting and instead set the Style option to Constrained Aspect Ratio (renamed Fixed Aspect Ratio in Elements 2.0). With this option, the values you enter in the Width and Height boxes establish just the proportions of your outline. If you want a picture to fit a 4 x 6-inch frame, for example, you simply enter 4 and 6 as the Width and Height values. You also can enter a specific pixel count, but you're limited to a top value of 999.999 pixels.

After entering the values, drag in your image to create a new selection outline. You can make the outline as large as necessary to surround the parts of the picture you want to keep. No matter what the size of the outline, the Constrained Aspect Ratio feature ensures that the proportions of the outline remain the same as the one you originally drew.

After you apply the Crop command, you can downsample — that is, dump excess pixels — to arrive at the right output resolution or screen size.

To crop the photo more tightly: There is no perfect solution for this one. If you retain less of the original photo than indicated by the marquee you created in Step 6, you wind up with fewer pixels than you need to achieve the output resolution or display size you want.

For a print picture, you can try reducing the resolution value you used to calculate the pixel dimensions in Step 4. This results in a smaller selection outline when you click in Step 6. But remember that using an image output resolution lower than your printer suggests may reduce the quality of the print.

For an on-screen image, you can select the Constrained Aspect Ratio option and draw the selection outline as explained in the preceding bullet point. This time after you crop, you need to upsample — add pixels — to wind up at the display size you want. However, upsampling typically results in lower image quality, too.

To be honest, in this situation, you'll probably want to draw the selection outline with the Constrained Aspect Ratio regardless of whether your photo is meant for screen or printer. After you choose the Crop command, check to see where you're at in the pixel department. If you're not too far off, just move along, recognizing that you're sacrificing a little bit of image quality in order to arrive at a certain picture size.

Of course, if you're working with a scanned image, you can always rescan the picture. When you rescan, use your scanner software's crop function to scan just the area of the photo you want to retain, making sure to set the input resolution high enough for your planned output.