Increasing Image Size To Make Large Prints


© 2002 Gregory Georges

© 2002 Gregory Georges


© 2002 Gregory Georges


© 2002 Gregory Georges


Dragon Fly Canon EOS D30 digital camera, 300mm f/2.8 IS with 24mm extension tube, ISO 100, 16-bits per channel RAW image setting, f/7.1 @ 1/160,18.7MB 2160 x 1440 pixel .crw file has been edited and cropped to a 1800 x 1440 pixels 8-bits per channel, 7.8MB .tif

When using a film, flatbed, or drum scanner to scan film or photographic prints, getting large enough digital image files is usually not a problem. However, as more photographers begin routinely using 2-, 3-, 5-, and now 6-megapixel digital cameras, which are currently the common and affordable sizes — getting a large enough image to make high-quality 8" x 10"s, 11" x 14"s, 16" x 20"s, or even larger prints is often a problem.

The problem of increasing image size while retaining image quality is one of the most challenging unsolved mathematical problems facing those involved in digital imaging research. Being able to get a large high-quality image from a small image file would reduce the time it takes to process images (see Technique 17), would allow images to be transferred online and between devices more quickly and with less bandwidth, and would help to minimize storage requirements. So, if there were a good solution today, we'd all be enjoying it and the inventor would have plenty of money to enjoy!

So, the multi-million-dollar question is: How do you increase the size of an image without suffering from image degradation? There are many answers (and opinions) to that question and in my opinion, each good answer always starts with "it depends." How far you can res-up an image depends on a number of image characteristics and how critical it is to have a sharp, in-focus image instead of one with the dreaded (or sometimes desirable) pixelization or softness that comes from adding pixels in places where there were previously no pixels.

While there are many rules or recommendations about when and how to use different techniques to increase the size of an image, I recommend that you learn about three different approaches and then experiment to get the results you want. Without question, many of the new digital SLRs and prosumer-level digital cameras have greatly changed my view of how far you can up-sample an image. Many digital cameras create totally grainless digital photos. If a digital picture is in focus and grainless, it can be enlarged much more than a scanned image that contains digital noise (the equivalent of film grain). Soft blurred digital photo can also have a remarkable smoothness to it that allows such a photo to be increased many times its original size.

One other factor that can limit how large an image can be increased is how much the image needs to be sharpened. In Technique 12, the point was made that an image should not be sharpened until it has been sized for its intended use. The process of up-sampling an image will at some point create visible pixelization; sharpening an image with moderate pixelization can result in a wholly unsatisfactory image. Likewise, upsampling an image that has already been sharpened can cause an even nastier problem — upsampled sharpening! Remember that you can't actually sharpen an image; you can only increase the perception that an image is sharp by creating more contrast along the edges of an image and this increase in contrast normally does not up-sample well.

Presently, digital photographers can take any one of three different approaches to increasing image size. These approaches are:

1. Use one of the several available image resolution-upping plug-ins, such as Lizard Tech's Genuine Fractals. Many digital imaging experts have argued for years over the merits of the leading resolution-uppingplug-ins with no real definitive agreement that you can get better results using one of the plug-ins than you can when using the Photoshop 7 Bicubic Interpolation method, which can be found in the Image Resize command — for original images that are under 20MB in size. Few question the decided benefits of using these plug-ins for increasing larger original files (20MB or larger) to poster size or even larger when the res'd-up prints are to be viewed from a distance. However, the consensus view is that these plug-ins are not as useful as one would like them to be when increasing an original digital camera image file size when using up to a 6-megapixel digital camera to make large prints in the 11" x 14", 16" x 20",or even larger sizes.

2. Allow printer hardware to increase image resolution when printing. Depending on the printer model and its image interpolation capabilities, and the characteristics of a given photo, some printers can do a very good job at modestly increasing image size. Specifically, the Lightjet 5000 printer has such capabilities and it is widely accepted opinion that the Lightjet 5000's hardware interpolation does a better job of increasing image size than the Photoshop Bicubic interpolation or any currently available plug-ins. How much a file can be increased in size by various printers is once again subject to the characteristics of a given image and the acceptance level of image softness.

3. Use the Photoshop 7 Image Size command. Never underestimate what it can do!

Okay — enough talk; time to increase the size of the digital photo of the dragonfly by 300%. To illustrate some of the points made previously, this photo was chosen for enlargement because it will readily show softness if it is increased too much and because it needs sharpening to make the wings look their best. As you further increase image size, sharpening has a tendency to worsen the negative effects of up-sampling an image.

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