How to Scan Film Photos for Photo Enlargement

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Over the years I've had numerous customers send digital image files from film photos they have scanned and request photo enlargement and prints. In almost every circumstance, the files received were scanned at too low a resolution to produce photo enlargement without resampling the original digital file to produce the requested print size. Every time you resample a digital file, the original image quality will degrade, producing a lower visual quality photo enlargement.

There is a simple technique we use when scanning film photos for photo enlargement that will produce the exact print resolution required for your particular digital photo printing system. All you need is a good quality scanner that can scan with an optical scanning resolution of 2400 dpi or more, and has a scanning setup mode that allows you to enter specific sizes and resolutions, with an image output scale or percentage listed. You must also be able to "select" the original photo with a marquee selection tool, or a similar manner to select and scan only the area of the photo.

When I say "Optical" scanning resolution I mean strictly optical. All scanners will have listed scan resolution available that are extremely high. These are usually interpolated or digitally resampled resolutions. You may have to check the scanners specifications to find out what it's actual optical scanning limit is. Any resolution used that is higher than the listed optical resolution, will resample the digital image.

The scanning setup window or mode must allow you to enter specific parameter sizes for the output image, and allow you to enter specific scan resolutions or dpi. Most better quality scanners will have a "professional" type mode you can access to set up your scan. You will not be able to use this photo enlargement technique with the "quick scan" or "auto scan" type of application.

To fine tune the output image, or to crop to an exact print size, you should also have installed an image editing software such as Photoshop. The scanned image will not usually come out as an exact print size.

This photo enlargement technique will work equally well with any type of original film photograph. If your scanner can accept negatives or transparencies, the same process can be used to format photo enlargements from these types of original film photographs.

To illustrate this photo enlargement technique, we will be scanning from Photoshop CS using an original 4x6 photo print. To set up the scan, you need to know just two specific items. One, the size of the photo enlargement or output print size. Two, the resolution or dpi required for printing the photo enlargement. We will produce a photo enlargement of 11x14 at a printing resolution of 300 dpi.

Step One:
Place the photo on the scan bed and open the scanner setup window. Preview the photo and select the entire photo with the selection marquee. We will say the photo is a portrait orientation photo, with the photo height as the long side and vertical.

Step Two:
Enter 11 inches in the width field of the scan setup window destination or target section. You will see a corresponding height of 16.38 inches. If you were to enter 14 inches in the height field, the image width would only be about 9 inches, not large enough for your target photo enlargement. Here you may need to enter your target dimensions in either the width or height to determine which you need to enter to produce a large enough photo enlargement size. You can crop the photo enlargement to the exact print size later in Photoshop.

Step Three:
Check the scale or percentage field of the scan setup and you will see the dimensions you entered in the target size fields produce a 273% photo enlargement. This actually relates to a photo enlargement of 2.73 times the original photo size. Since you know you want to print the photo at a resolution of 300 dpi, you need to scan the original photo at a resolution of 300 x 2.73, or 819 dpi. Enter 819 dpi in the destination or output section resolution of the scanner setup window.

Step Four:
Since the actual photo enlargement will be produced through the digital image resolution, you then set the scale or percentage back to 100% and enter the original sizes or 4 inches width and 6 inches height back into the destination or output sizes in the scan setup.

Step Five:
So you should have your scanner setup with the original photo sizes of 4x6, at a scale of 100%, and a scanning resolution of 819 dpi. Go ahead and scan the image into Photoshop. Check your final image size in Photoshop by Image > Image size. We ended up with an image 4.029 x 6.0 at 819 dpi. To create the photo enlargement, simply uncheck resample in the image size window, and enter 300 in the resolution field. This will create an image 11x16.38 at 300 dpi.

Step Six:
To crop the photo enlargement to an exact 11x14, just select the crop tool, enter in the crop parameters width 11 inches, height 14 inches, and resolution 300. Drag the crop box over the entire image and position as you like. Click the crop check mark in the upper right of the screen and you have a perfectly sized 11x14 image at 300 dpi resolution ready for printing with no image digital resampling or re-sizing.

The whole point with this photo enlargement technique is to first, use the scanner settings to determine the scanning resolution dpi needed to produce the target photo enlargement size, then scan the original photo at the original size and 100% scale. When you scan a photo at it's original size with the "scale" at anything but 100%, the scanner software resamples or interpolates the digital file. This will produce a lower visual quality image.

More information on photo enlargement of film photos can be found on our Website, or if you have any questions concerning this photo enlargement scanning technique, feel free to contact me.

About the Author

Mike Kruske established PhotoArt Imaging Digital Arts Center in 1997 specializing in Photo Enlargement, Digital Photo Enlargement and Wide Format Digital Photo Printing of Digital Images. This targeted experience provides a unique insight into digital photo processing for large format print output. More info here:
PhotoArt Photo Enlargement and Digital Photo Printing.

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