Digital Camera Info

Technical Information

Image Size

Digital cameras typically state their resolution in "Megapixels". This is the number of millions of individual pixels – or dots of color – that are captured. Considering that most images are rectangular (4:3 ratio), this translates into a few thousand pixels both horizontally and vertically (the exact numbers of which can vary from camera to camera).

Print Size

The printed size depends on the chosen print resolution in pixels per inch (ppi). Fewer pixels will produce less detailed printouts, while more pixels (up to a certain point) will produce sharper printouts. The table shows achievable print sizes based on printing at low resolution (200ppi), medium resolution (300ppi) and high resolution (400ppi).

Which Resolution?

Many glossy magazines, jewellery catalogues and other materials that we would consider "sharp" are produced with the images printed at 300ppi. Images can be printed at a lower resolution if they will be viewed from a distance (eg. when hung on a wall) or at a higher resolution if finer detail is needed. For example:

• 100ppi = Billboards on city streets;
• 200ppi = Posters, draft prints;
• 300ppi = Glossy magazines, general personal prints;
• 400ppi = Fine art books, high detailed prints;
• 500ppi = Finest detail (beyond many people's eyesight)

Printer Resolution

Don't confuse the above image printing resolutions in ppi (pixels per inch) with print resolutions in dpi (dots per inch). Most printers need several dots of print resolution to reproduce a single pixel of image resolution. This is because printers typically use only four colors: Cyan, Magenta, Yellow and Black. These colors are "mixed" on the page to simulate the whole spectrum of colors required for reproducing photographic images.

For example, take a typical four-color inkjet printer. To print a single "tan" pixel from a digital photo of someone's face may require one dot of Cyan ink, two dots of Magenta ink, three dots of Yellow ink and one dot of Black ink.

A tried-and-tested rule-of-thumb for sharp printouts is to print images at around 1/4 the resolution of the printer. Thus a typical four-color laser printer, which may have a print resolution of 1200dpi, can produce sharp printouts from images printed at 300ppi. Printing at any higher density (eg. 400ppi) would simply lose those extra pixels in the "gaps".

Other Considerations

According to the above table, a camera of five megapixels is about the minimum needed to produce sharp prints and decent enlargements. Why would anyone need more megapixels?

Reducing Moiré

One type of moiré is the geometric pattern that appears when looking through two mesh screens (such as flyscreens) in front of each other. Basically, it's because the holes in the front mesh don't line up exactly with those in the rear mesh (due to perspective). One hole lining up with the hole behind will appear light, while another hole lining up with the mesh behind will appear dark.

Another type of moiré is the wavy lines that can appear when taking a digital photo of someone wearing a patterned material (eg. houndstooth, fine checker, even a coarse weave). This is due to the camera's pixels lining up with either dark or light parts of the pattern in the cloth.

Having a higher resolution digital camera will reduce the chances of moiré patterns.

Zooming and Cropping

Sometimes it is necessary or desirable to zoom in on a portion of an image or to crop something unwanted from an image. For example:

• Printing one or two faces out of a group shot;
• Zooming in on the detail of a tiny insect;
• Adjusting a sunset scene so that the sun is centered.

All of these examples are effectively discarding a portion of the image. Having plenty of megapixels to begin with means that there will still be sufficent pixels for the remaining image to be sharp.