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|| News Item: Posted 2004-06-30

Pushing Pixels: Digital Myths
By Reed Hoffmann, Blue Pixel

Flipping through the TV channels a few weeks ago, I ran across a show called "Myth Busters." Gave me an idea for a column. Whether talking to people or reading stories on the web, in newspapers or magazines, I constantly run into common misconceptions about digital photography. It's time to clear the water on some of them.

WYSIWYG - Most people know that this stands for "What You See Is What You Get." That came from the early days of publishing via computer, meaning that what you saw on screen was what would come out of the printer. Cool stuff at the time, and if you stop to think about it, still cool today. Unfortunately, a lot of people think this also refers to looking at photos on a computer screen, and sadly that's just not true.

Unless you're running color management properly (meaning a good hardware/software combination using a colorimeter or spectrophotometer, and both calibrating and profiling the monitor), the colors of the photo you're looking at on screen may not even be close to what's really there. So making decisions on color, tone, saturation and the like on an un-calibrated screen may actually take a good picture and make it bad. That's why learning to tone by the numbers in the Info box (Using K Value, RGB and CMYK) is so important to photographers working on laptops, which are nearly impossible to calibrate and profile properly.

To make matters worse, even if you're working on a properly calibrated and profiled monitor, just toning by look isn't enough. If your end process is ink on paper, then that image has to go through a conversion to CMYK, and that means keeping as much data possible in the image is critical to best reproduction. Making an image look good on an RGB monitor doesn't mean it will reproduce well, just that it will look good on an RGB monitor, which is fine if you're going straight to web. As always, getting the image right in the camera and doing as little as possible in Photoshop is what you should be trying for.

PPI vs. DPI - Okay, this one that drives me nuts. PPI means "Pixels per Inch," and applies to camera images and working in Photoshop (or other editing apps), and tells you how many pixels an image has per square inch. A six-megapixel camera has about six-million pixels, so if you take all those pixels and spread them out with a density of 200 PPI, they would cover an area about 15-inches wide by 10-inches deep. A four-megapixel camera, with 4-million pixels (okay all you math majors, that's a smaller number, right?), at that same 200 PPI will cover an area 12-inches by 8-inches. Fewer pixels mean a smaller print size at the same PPI.

DPI stands for "Dots per Inch," and ONLY APPLIES TO PRINTING. Sorry about the caps. Dots per Inch relates to how many dots of ink a printing process can put down in a one-square-inch area. Inkjet printers usually start at 720DPI and go well beyond that, as high as 5760 DPI and beyond. 720 DPI, by the way, is considered "photo quality." So I never want to hear any of you saying that you cropped or prepped an image to XXX DPI, since you're not doing that. When you're working with an image, it's always PPI. DPI only comes to play in the printer dialog, when you choose what quality to print at. Got it?

Sensor Cleaning - All right, everyone agrees that dirty sensors are a pain, but everyone doesn't agree on right and wrong ways of cleaning them. Fine. Just don't believe the popular urban myth that blowing off the sensor while keeping the mirror up and shutter open with Bulb makes things worse. There's a popular story going around that doing this will actually attract dust to the sensor, since the sensor is being charged (you're making an exposure in Bulb, right?). When asked about that, one of the camera company's engineers laughed, saying you'd have to charge the sensor for about a week to build up enough charge to attract dust. End of that rumor, okay?

More Pixels is Better - What do you say when somebody walks up to you at an assignment and points out that their point-and-shoot has more pixels than your SLR? You tell them, "Not all pixels are created equal." SLR cameras have larger pixels, which mean a cleaner signal, resulting in a less-noisy image. Ever shoot a point-and-shoot at 800 ISO? Yuck! In addition to larger and better pixels, the processing that happens in an SLR is usually higher-quality, resulting in better quality files. Next time someone tells you they've got more pixels, tell them your camera cost $3000, and that you get what you pay for.

Keep those cards and letters coming, or at least emails (sportsshooter If you've got a good digital myth you're curious about, send it along. I'm always looking for a topic that would make for a good column.

(Reed Hoffmann's a former newspaper photographer and now partner in Blue Pixel (, a digital photography consulting and training company.)

Related Email Addresses: 
Reed Hoffmann: sportsshooter

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