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Digital Camera Info
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Family and friends often ask my advice on digital cameras. Here's some technical info that you may also find
enlightening.
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From Film To Digital
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Introduction:
Having always been interested in both photography and computer graphics, it was natural that I would be one of
those who experimented with an early model low resolution digital camera. When the higher resolution cameras at
last became affordable, it brought up the interesting question of whether technology had reached the stage where
I could replace both my digital camera (which was used for low quality but instant results) as well as my film
camera (which was used for producing higher quality prints for photo albums, sharing with friends, reprinting,
enlarging, etc).
A city camera store that I visited tried to make this easy by relating the "Megapixel" rating of a camera (ie. how
many million dots make up the image) to a typical print size. Not satisfied with their optimistic calculations, and
not convinced by their sample prints, I performed my own calculations, which I'll present in the following table.
For those technically minded, I'll explain it underneath.
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MegaPixels vs Printable Size
How large you could expect to print at typical "Detailed" resolutions?
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Mega-
-Pixels |
Image Size
(Pixels) |
Print Size
@ 200ppi |
Print Size
@ 300ppi |
Print Size
@ 400ppi |
| 1.0 |
1155 x 866 |
5.77" x 4.33" |
3.85" x 2.89" |
2.89" x 1.87" |
| 2.0 |
1633 x 1225 |
8.16" x 6.12" |
5.44" x 4.08" |
4.08" x 3.06" |
| 3.0 |
2000 x 1500 |
10.00" x 7.50" |
6.67" x 5.00" |
5.00" x 3.75" |
| 4.0 |
2309 x 1732 |
11.55" x 8.66" |
7.70" x 5.77" |
5.77" x 4.33" |
| 5.0 |
2582 x 1936 |
12.91" x 9.68" |
8.61" x 6.45" |
6.45" x 4.84" |
| 6.0 |
2828 x 2121 |
14.14" x 10.61" |
9.43" x 7.07" |
7.07" x 5.30" |
| 7.0 |
3055 x 2291 |
15.28" x 11.46" |
10.18" x 7.64" |
7.64" x 5.73" |
| 8.0 |
3266 x 2449 |
16.33" x 12.25" |
10.89" x 8.16" |
8.16" x 6.12" |
| 9.0 |
3464 x 2598 |
17.32" x 12.99" |
11.55" x 8.66" |
8.66" x 6.50" |
| 10.0 |
3651 x 2739 |
18.26" x 13.69" |
12.17" x 9.13" |
9.13" x 6.85" |
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Above Table Explained
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What Is "Standard" Resolution?
The commercial printing industry has a tried & tested calculation for printing sharp colour images. Your source
image needs to be around 1/3 to 1/4 of the resolution of the printer. Typical printing presses run at about 1200
dots per inch (dpi), thus they commonly print images at 300 pixels per inch (ppi). This is the case for the
jewellery catalogues that I produced for a jewellery company.
The Wrong Resolution:
Using images of a higher resolution will produce little or no visible increase in quality, as the extra pixels
of detail are lost in the "gaps" between the printed dots. However, too low a resolution will produce blurry
printouts, or ones where pixels start to show up as individual "blocks" and angled lines appear jagged ("staircase"
effect).
Higher Resolution Printers:
Today's inkjet and dye sublimation printers can typically print at resolutions of 2000 dpi or more. If you observe
the same rule of ensuring that your images are 1/3 to 1/4 of that printed resolution, this means that they should
be of higher resolution than 300ppi, more like 400 to 500ppi. However, above a certain point, you won't notice the
individual dots, so 400ppi is probably sufficient.
Conclusion:
I figured that if I wanted to replace my current film camera with a high-res digital camera, it would have to be
able to print a sharp 6" x 4" (150mm x 100mm) standard sized photo and a clear 8" x 6"
(200mm x 150mm) enlargement.
By my calculations, this means that a 5MP camera would be adequate, and in fact would be suitable for most people.
So that's what I bought, and it's working out exactly as I predicted.
Postscript:
One limitation that I did notice recently, and one that I've never heard mentioned in camera stores, is something
called "moiré". This is the weird checkerboard patterning effect you notice when looking through two mesh
screens (like flyscreens) in front of each other. Without getting too technical, it's because the holes in the
front mesh will never line up exactly with those in the back mesh because of perspective.
Well, try taking a digital photo of someone wearing a houndstooth patterned suit, or any fine checked pattern, or
even a coarse weave. The result may have quite a noticeable moiré pattern due to the camera's pixels lining
up with either dark or light parts of the pattern. The only solution to this is an even higher resolution digital
camera.
Finally, having a higher resolution shot allows you to use a portion of a photo and still have enough remaining
pixels to get a sharp print. You could zoom in on a small amount of detail, or crop an image to remove something
unwanted or improve the composition. For example, you could print one or two faces out of a group shot, or print
a portion of a sunset shot so that the sun is centred. Having more megapixels obviously gives you more original
detail and therefore allows you to choose to print smaller portions of any photo.
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This page last updated: 01-Mar-2008. Copyright © 1999-2008 by
Ian W. Fieggen. All rights reserved.
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