PHOTOSHOP TIP: Enlarging Digital Camera Files
By Michael Frye

The problem with most digital cameras is that they simply don't capture enough information to make large prints. Smaller prints, up to 8 x 10 inches, are no problem for most newer models -- at least those that capture 4 megapixels or more. But larger prints, 16 x 20 and up, are still problematic.My Canon 10D, a 6.3 megapixel camera, produces images that are 3072 x 2048 pixels, which means that I can make a 10 x 15 inch print at 200 dpi. 200 dpi is the minimum resolution I use for continuous-tone printers like the Lightjet or the Chromira. For most inkjet printers, like the Epson 9600 that I use, you can set any resolution you want, but below a certain point the image starts to look fuzzy and show individual pixels, especially along diagonal lines.

Where is that point? That's a subjective matter, but for me it falls somewhere between 150 and 200 dpi. At 200 dpi, the image looks clean and sharp. At 150 dpi, it starts to fall apart. So, for the purposes of this tip, I'll use 200 dpi as the minimum resolution necessary for printing.For me to make prints larger than 10 x 15 from my 10D, yet still keep the resolution at 200 dpi, I have to create more pixels. Rather, I have to let Photoshop or some other program create more pixels. There are a lot of ways to do this. Some work better than others, but no program can invent detail that the camera didn't capture. The best you can hope for is to preserve as much information as possible.I'll examine four different methods of enlarging digital camera files, and then show you samples of each so you can make up your own mind about which works best. But first I want to put in a good word (a plug?) for Adobe's RAW plug-in.

Adobe RAW Plug-in
Adobe released the first version of this as a separate, $100 piece of software that could be used as a plug-in with Photoshop 7. It is now included in the new Photoshop CS, and the new version supports a wider range of cameras. At the bottom of this page, you'll find a list of the cameras it supports.If you work with RAW files, this plug-in alone is worth the price of the upgrade to Photoshop CS. It makes working with RAW files much easier, and has a host of great features. For example, it has some excellent noise reduction tools, and tools for reducing chromatic aberration (color fringing). It has a color temperature slider that makes warming filters obsolete. But best of all, and most relevant to this discussion, it improves image quality. I'm not sure how, but it does. Here's a comparison from the image above. The files have not been enlarged or resampled, but one was processed using the Canon software that came with my camera, the other with Adobe's RAW plug-in (neither has been sharpened):

The differences are a bit hard to distinguish on screen, but you can see how the bumps on the ridge line disappear with the Canon software, and how Adobe's RAW plug-in brings out more definition in the tree branches. No, I don't get paid by Adobe! But they do get it right sometimes. Note that I haven't compared the RAW plug-in with Nikon's software, or Fuji's, or anyone else's -- just Canon's. Perhaps the other manufacturer's software is better. Let's hope so!

Enlarging a Digital File
Next we'll look at four methods of resizing a digital camera file: Photoshop's standard bicubic interpolation; the stairstep method; using Photoshop's RAW plug-in; and Geniune Fractals, a popular third-party software product.

Photoshop's Bicubic Interpolation
If you go to Image > Image Size in Photoshop, and check resample, the default method of resampling, or interpolating, is bicubic. (Photoshop CS also adds the options of bicubic smoother and bicubic sharper but for the sake of simplicity I will ignore these for now.) Regardless of what method you use, enlarging a file means inventing pixels. Photoshop's bicubic interpolation looks at adjacent pixels and then decides what the new, in-between pixels should be by splitting the difference. In other words, if one pixel is black, and an adjacent pixel is white, Photoshop will make the new intermediate pixel gray. The result is a more gradual transition from black to white and a loss of sharpness or definition.The Stairstep Method
This also involves using Photoshop's bicubic interpolation, but enlarging only ten percent at a time (note that in Photoshop's Image Size dialog, you can change "Inches" or "Pixels" to "Percent"). The theory is that this will help preserve edge definition.

Using the RAW Plug-In
If you shoot in RAW format, you can resize the image right in Photoshop's RAW plug-in. Because the interpolation is done with the raw, linear data that the camera captured, theoretically this will produce a better result.

Genuine Fractals
This popular software is designed to enlarge files yet preserve edge definition. Basically, if it sees a black pixel next to a white pixel, rather than creating a gray pixel in-between it will create either a black pixel or a white pixel, thus preserving a sharp edge. It retails for about $160 (www.lizardtech.com).

Comparing these methods
I took the same RAW file from my Canon 10D and enlarged it to 16 x 24 inches at 200 dpi, then cropped out the small sections below. In each case, I started by processing the RAW file in the Adobe RAW plug-in, since, as shown above, this gave better results than the Canon software. I used no sharpening in the initial processing of the RAW file, but gave each file a slight amount of final sharpening in Photoshop after the image had been resized (Amount 400 percent, Radius 0.4, Threshold 0).

Bicubic

Stairstep

RAW Plug-In

Geniune Fractals

Results:
It's hard to tell the difference between the first three samples. Of these I would give a slight preference to the RAW plug-in. Genuine Fractals shows the biggest difference: edges, particularly between the mountains and sky, are sharper. But a close look at the trees reveals some strange artifacts, almost like JPEG compression.While Geniune Fractals produces sharper edges than the other methods, and makes prints that appear sharper overall, sometimes that comes at the expense of other, subtler details. What should be smooth transitions can become abrupt edges, resulting in a strange, "digital" look. I've created two other samples below. Note how in the first sample you can actually see less detail in the veins of the aspen leaf in the Genuine Fractals version, while in the second sample the RAW plug-in creates a smoother transition from the light to the shaded side of the branch.

Whether you like Genuine Fractals is a matter of preference -- whether you prefer a print that initially looks sharper, but might look a little strange upon close inspection; or whether you prefer the smoother, more natural look of the other methods.There is no perfect solution. With the best enlargement methods, I think my Canon 10D images are comparable to images captured with fine-grained 35mm film, but they don't hold up to medium format film.The biggest difference I found in these tests was not in the various enlarging methods, but between processing RAW files with the Adobe RAW plug-in versus Canon's software. The RAW plug-in is a big improvement and a pleasant surprise.Michael Frye is a professional photographer based in Yosemite National Park. His articles and images have appeared in Outdoor Photographer, American Photo, and in many books, calendars and posters. Click to visit his website.

Cameras Supported by the Photoshop CS RAW plug-in:

Canon
EOS-1D
EOS-1Ds
EOS-10D
EOS-D30
EOS-D60
EOS 300D (Digital Rebel/Kiss Digital)
PowerShot 600
PowerShot A5
PowerShot A50
PowerShot S30
PowerShot S40
PowerShot S45
PowerShot S50
PowerShot G1
PowerShot G2
PowerShot G3
PowerShot G5
PowerShot Pro70
PowerShot Pro90 IS

Fujifilm
FinePix S2 Pro Leaf
Valeo 6
Valeo 11

Konica Minolta
DiMAGE A1
DiMAGE 5
DiMAGE 7
DiMAGE 7i
DiMAGE 7Hi

Nikon
D1
D1H
D1X
D100
Coolpix 5700
Coolpix 5000 — with firmware version 1.7

Olympus
E-10
E-20
C-5050 Zoom

Text and photos ©2004 Michael Frye, All Rights Reserved. This page may not be reproduced without the permission of the copyright holder.