Preparing images for printing
If you felt confused by the tutorials on preparing images for the screen, you will be happy to know that you don't absolutely have to prepare them first. You'll get better results, but it's not strictly necessary. This is covered in "Using a photo lab in a store" and "Printing at home" .
The simple steps
A lot of the steps for preparing your images for printing are similar to preparing them for viewing on the screen. The main difference is that you don't want to make them quite as small and you need to crop in the same ratio as your print size.
The simple version
This is what you need to do to your photos to prepare them for the web.
- Rotate the image 90° counter-clockwise
- Crop the image to the print ratio of the size you are printing
- Perform an auto-enhance command (whatever your photo editor has)
- Apply a slight sharpening, if your photo editor has that function
- Change the image size so that the image is between 150 and 300 dpi for the size you are printing
- Save your changes
For more details, read on:
Rotating
Rotating for printing is the same as rotating for web use.
Cropping
Even if you are happy with the size of the subject, you may need to perform some cropping if you are planning to print the image. This is because standard print sizes have different ratios. The camera takes images in the 1.5 ratio. This is the same ratio as a 4x6, 8x12, 16x24 and 32x48 print. Therefore, If you make a 5x7, 8x10, 11x14, 16x20, 18x24 or 20x30 print from your image, either you have to crop away some of the top and bottom or you have to have a white strip on the left and right to maintain the print ratio.
Using Photoshop
There are several ways to crop to a ratio in Photoshop Elements. The way we recommend is to set the Marquee tool to use “Fixed Aspect Ratio” as the Mode and type in the size of the print you want to make into the width and height boxes. This is the simplest method and has the least pitfalls.
In this example, we're cropping for an 8x10 print size.
Using iPhoto
In iPhoto, there is a Constrain drop-down. Simply select the size of the photo from the drop-down,
Crop marks in the correct ratio are then automatically super-imposed over the image. Adjust them so that the subject is not chopped off and is as big as possible. 
Then press the Crop button when done. 
Enhancing the color and exposure
When enhancing the image for the web, we made it look nice on our screen. Sure, not every computer monitor will show the colors the exact same way, but our monitor is the only one we have control over so it's the only one we worry about.
When enhancing for printing, however, we need to worry about how the printer we use will render those colors. Professionals use a color calibrated monitor and download ICC profiles to match every lab they use. They may even develop ICC profiles for every printer they own.
This is expensive and too much work for most people. Most continue to adjust their images based on how they look on the screen and then print them to their ink jet printers. If the print comes out too dark or lighter or with a color cast, they make their best guess on how to adjust it and print again. This “good enough” approach may waste a bit of paper but it works.
If you are sending your images to the same lab, you will get a feel for how your monitor matches their printer. If you aren't sure, most labs will do an equivalent of “Auto Enhance” on your images as they print them. If you are going to use your lab's automatic adjustment feature, you may want to skip doing a lot of adjustment on the image yourself since every adjustment can increase the noise of the image and introduce “artifacts.”
Sharpening
As explained under “Preparing images for the screen”, some sharpening is needed on almost every digital image. The principles for how to sharpen aren't different if you are preparing an image for printing instead of the web. However, the printing process will make your images appear slightly softer than they appear on your screen. Therefore, you need to be slightly more aggressive when applying sharpening
Down-resing or Down-sizing
When preparing images for printing, you need to supply enough pixels to the printer. For most printers, 150 pixels per inch is okay though you may want to provide a bit more. Some labs ask for 300 dpi but that can make a pretty big file and probably isn't necessary. For most labs, 200-250 dpi works best.
If you are saving your images on a CD and taking them to your local lab, it doesn't matter if they have more then 150-300 dpi. But if you are uploading them to an online lab, the bigger your files, the longer the upload takes and the more likely it is to fail. Therefore, you may want to down-size them first.
Follow the directions under “Preparing images for the screen” to do the down-sizing. Read the tutorial on “Using an online lab” for a table of sizes to use for each print size.
When you need to upsize
What if you have cropped your image so much that there aren't enough pixels to print at the size you want? You have two choices. One is to print a smaller size. The other is to “up-size” your image. If you have a program like Photoshop Elements, you can use the "Image Size" command to do this. Upsize in small increments, making the image no more than 10% bigger each time.
If you don't get good results doing this by hand, try the free plug-in “Interpolate THIS.”
Poster sizes
If you are trying to make a poster -- sizes of 20x30 or larger -- there are a number of labs that specialize in this type of work. Most of these labs don't require you to upsize the image -- they do this part of the work for you, often with spectacular results. You can find them via a simple web search. You may want to use a local lab so you can talk to them on the phone first and deliver your image via a CD (much faster than uploading it to a web site!)
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