May 11, 2005

The Resolution Solution

By Scott Bourne

Most digital camera buyers mistakenly believe that the camera with the most megapixels offers the best image. Here is a case in point: Cammie Camerabuyer goes to the digital camera superstore and says "Shouldn't I get the camera with the most mega pixels? I think I always want the one that gives the highest resolution," she said.

(If this were a radio commercial I would insert the sound effect here. It would sound like one of those annoying buzzers on a game show. "Ehhhhhhhh!") Wrong lady. The most mega pixels do not mean the best image!

This is one of the most misunderstood areas of digital photography. Many workshop leaders who are otherwise great photographers and teachers routinely get it wrong. Early college textbooks had trouble describing it. And the salesman at the local camera store is more likely to be an expert at linear algebra, have the winning lottery numbers and a guaranteed cure for cancer than he is to truly understand camera resolution.

The dictionary definition of mega pixels is one million pixels. Oh, if it were only that simple.

I have been working in the digital domain for 13 years and from time-to-time, even I have been somewhat confused about digital resolution. But now, after a long road, I believe I understand it. The reason that I think I understand it is simple. I think I can explain it.

So here goes:

It starts with this basic truth: Pixel quality and pixel quantity are independent of each other--period! Allmost all of the serious digital camera reviews contain this fact if you look closely. Many don't say it this plainly and some miss it altogether, but it is something that should be discussed more.

People use the mega pixel rating to determine the "value" of a digital camera. Look at any of the web discussion groups. As soon as a new camera comes out with more mega pixels, people start talking about dumping their old camera for the new one. But not all mega pixels are the same. Many factors go into rating a digital camera. Counting mega pixels is only one of them. Before you decide that a six-mega pixel Canon D60 and a six-mega pixel Phase One back are equal, look at a 20x30" print from each. How is it that one is dramatically sharper than the other? Why is it that the print from the Phase One has so much more detail if mega pixels are all that matter?

Again, the number of mega pixels alone does not equate to picture quality.

1) You need to know the size of the capture chip. Bigger is better.

2) You need to know the size of the mega pixels and how they are arrayed. Larger pixels are better than smaller ones.

3) You need to know whether or not the mega pixels are captured with a CMOS, CCD or FOVEON chip. Each is different and has definite strengths and weaknesses.

4) You need to know the size of the chip. Bigger is better.

5) You need to know the quality of the chip. Low, medium or high grade CCDs for instance are exponentially more expensive to manufacture.

6) You need to know whether or not the chip's native software interpolates the image. You will get better images if the interpolation is done post capture.

7) You need to know if the chip is a one or three-pass sensor. Three-pass sensors, like those used in a Phase One or similar products will produce an image with three times the resolution and color depth as those with one pass.

8) You should ask about bit depth or what the ads call dynamic range. For instance, if one camera uses a 14-bit analog-to-digital (A/D) converter, (for a total of 42 bits spread over the three color channels) and the other uses a 12-bit A/D converter (for a 36-bit total) but the latter has more mega pixels, which makes the best image?

In other words, you need to consider at least eight criteria other than the number of mega pixels to accurately judge the quality and value of a digital camera.

All of this is designed to make you think. In the digital age, there is a great deal of misinformation. Ask questions and look at all of the camera's specifications. If your local camera store guru says, "Camera X is better than Camera Z," tell him you want specific reasons for his opinion. Ask him about the eight factors listed above.

While no 1000-word article can give you a complete understanding of digital camera resolution, I hope I have convinced you that mega pixels are not the only factor that determines camera value and image quality.

If you want to learn more about this, search the web for information on each of the eight questions posed above. You will start to get a better feel for mega pixel madness. And even if you don't fully understand the answers, you will surely put your local camera guru to the test.

Sidebar

Output resolution, i.e., PPI, DPI and LPI is also commonly misunderstood. Here is a short explanation.

These terms are used to determine the difference in how resolution is measured depending on device. The Byzantine jumble of acronyms and jargon that is used to describe resolution is crazy. But never fear. Just memorize this concept, and you will understand more about it than most so-called experts.

When measuring DESKTOP PRINTER OUTPUT RESOLUTION, use dots per inch. DPI refers to the resolution of an output device like a laser printer or image setter. A standard office laser printer is 300 dpi. A standard image setter is 2,540 dpi.

When measuring PROFESSIONAL OUTPUT RESOLUTION, lines per inch LPI is the resolution (line screen) of a printing press, which determines how much detail the press (and the paper) can hold.

When measuring MONITOR/SCANNER OUTPUT RESOLUTION, use pixels per inch. PPI is the resolution (or detail) of an image in a scanning or graphics program, and the resolution of computer monitors: The standards are, 72 ppi for Macintosh and 96 ppi for IBM compatibles.

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ABOUT THE AUTHOR

Scott Bourne is a professional photographer, author, teacher and pioneer in the digital imaging field. His career started in the early 1970s as a stringer covering motor sports for Associated Press in Indianapolis. Since then, he has shot commercial, portrait, wedding, magazine and fine art assignments. His present passion is wildlife photography.

Scott is the author of "88 Secrets to Selling & Publishing Your Photography" and "88 Secrets to Photoshop for Photographers." Both are available from Olympic Mountain School Press, http://www.mountainschoolpress.com. His work has also appeared in books, magazines, galleries, calendars, on greeting cards, web sites and on posters.

Scott regularly lectures on a variety of photo and media-related subjects. He has appeared on national television and radio programs and has written columns for several national magazines. He is the publisher of Photofocus.com, an online magazine for serious photographers and also runs the Olympic Mountain School of Photography in Gig Harbor, Washington near Seattle.