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Tuesday, April 26, 2011

Fade In


Filters On Filters • How Big Can I Go? • Focus On Flowers

Labels: How-ToColumnTech Tips
How Big Can I Go?
Q I'n a previous issue of OP, I read that a camera with a native resolution of 16 MP can make a print up to 11x16 inches. On the other hand, the instruction manual for my 12 MP Canon PowerShot SX20 says that at its largest file-size setting, prints can be made up to 16x20. Moreover, I have made 13x19 prints with the SX20 that seemed very sharp and detailed to me. How many pixels are needed for specific print sizes?
J. Trammell
Via the Internet

A It depends. First, all megapixels are not created equal. DSLRs have considerably larger sensors than compact cameras such as the Canon PowerShot SX20. When the pixels are packed onto a small sensor versus the larger one, comparatively more noise is usually the result, and that translates to less detail and color fidelity. Second, different printers offer more or less capability for quality enlargement. A multiple-function desktop printer intended for quick, small prints and text won’t produce the same quality as a printer designed for professional enlargements using a larger range of ink colors. Third, the media on which the print is made can emphasize or obscure detail and affect the acceptable print size. Finally, all photographers don’t judge the quality of a print by the same standards. These variables are at the heart of disagreement about how large a print can be made from a particular-sized file.

Twelve megapixels on any-sized sensor will produce at the highest quality setting a file of 36 megabytes (8-bit). If you print the file straight out of the camera at 300 dpi, you’ll get an image of approximately 8x10 inches. Note that some printers are optimized at 200 dpi and will make larger prints from the same-sized file. To make larger prints, we instruct our image-processing software to interpolate the file to a larger size. The software essentially fills in the spaces between the pixels as the overall image is expanded. Here’s where the size of the sensor makes a difference because each of the 12 megapixels on the DSLR sensor is larger than the 12 megapixels on the compact camera sensor, and the data gathered by those larger pixels is of higher quality. How large can you go? Stop before the file begins to fall apart, that is, where degradation of the image’s color and sharpness are noticeable. And note that some specialty interpolation software, such as onOne Software’s Perfect Resize and BenVista’s PhotoZoom Pro 4, can significantly improve the quality of your enlarged files and facilitate larger prints.

The medium you’re printing on can make a big difference in both the artistic interpretation and the acceptable enlargement size of your image. Highly textured and absorbent papers, such as watercolor stocks, soften the image. Because detail isn’t the goal in a watercolor image, you can print them larger. The rough surface of canvas also softens details and slightly mutes the colors. A sharply detailed, brightly colored rendition is best printed on a hard-surfaced, smooth medium as in a gloss or semi-gloss paper. These stocks are unforgiving; they will reveal every flaw in your image, and bigger prints only will maximize the failings.

As the creator of an image, it’s up to you to determine how your vision is best conveyed to others in the form of prints. Still, one way to educate yourself about print quality is to pay critical attention to the work of others. Look for clarity and color, and check for the telltale noise and lack of sharpness—even pixilation (jagged edges)—that say a file has been stretched to the point that it falls apart. Go to high-quality, established photographic galleries to see quality prints; an excellent example is the Tom Mangelsen “Images of Nature” galleries across the country.

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