How does it work?

Unlike traditional cameras that use film to capture an image, digital cameras use a image sensor called a CCD. These sensors contain millions of photosensitive diodes called photosites. When the shutter opens, each photosite records the intensity or brightness of the light that falls onto it by accumulating a charge; the more light, the higher the charge. The brightness recorded by each photosite is then stored as a set of numbers that can then be used to set the colour and brightness of dots on the screen or ink on the printed page to reconstruct the image.  You have heard of a 3 Megapixel  or 6 Megapixel camera. This term is an indication of the number of photosites on the CCD. These photosites typically varies in size between 5 microns (0.005mm) to 20 microns (0.02mm). The smaller the size of the photosites, the more photosites can be fitted on a CCD. Thus the higher the resolution. This means that a 6 megapixel will have more and smaller photosites than a 3 megapixel camera.

Now for the catch. These photosites can only record scales of grey. In order for these photosites to record different colours (red, green, blue) filters are placed over them. So, on a 1.2 megapixel sensor you might have 300 thousand red, 300 thousand blue and 600 thousand green photosites. All three colours have to be recorded to make up a colour photo. So the question now is " do you still have 1.2 megapixel capability?"

 The background of the picture above will give you an idea of what the CCD will look like if magnified. 

A company called Foveon developed a three CCD system, each recording a colour. This results in much higher real resolution. With this system a 3 megapixels might really be a 3 megapixel camera. See illustration below:

Resolution?

A digital image is made up from thousands of different colour pixels. A pixel is a small square block. Have a look at the images below. The image on the right is a magnification of a portion of the image on the left. The small square blocks you see in the image on the right is called pixels.

The CCD can only record the amount of information collected by its photosites. Each dataset recorded by a photosite represents one pixel. Some manufacturers claim that their 3 megapixel cameras can deliver a 6 megapixel image. This can only be achieved by interpolation and is not the true data recorded. Interpolation is also used to magnify a image and for so called digital zoom system.

What is interpolation?

Some cameras have the option to save the image in the original TIFF format. This is wonderful. The TIFF file will be much bigger that the JPEG  files but the quality is much better. No interpolation or compression had taken place. If one want to edit any image, whether you scanned it or recorded it with a digital camera, the ideal is to have your original in TIFF format. You can then edit it and after you are completely done, save it as a JPEG. If one attempt to edit a JPEG image you will loose a lot of quality. IT DOES NOT WORK, DON'T EDIT A JPEG.

The table below shows print sizes obtained from different image sizes:

From above table it is clear that if you own a 1 megapixel camera, you can not print your images larger than 100x150mm. If you attempt to print an image larger than this it will have jagged edges like the photo below.

Light

With digital cameras we have the same problem with colour casts as with ordinary film. Where we use different types of film or filters for different type of light, a digital camera have build in white balance feature. Some cameras balances for white light automatically and with other cameras you can choose between "outside", "tungsten light" or "fluorescent light" conditions.

Cost effectiveness?

In the beginning film cameras still outperformed digital cameras on quality. But this is not the case anymore. You can have your ditial photographs printed at just about any photo lab. The advantage is that you only pay for the prints. You do not have to buy film anymore and you do not have to pay for the development of the film anymore.

Thus digital is more cost effective than film.

Conclusion

• If you are into taking good quality pictures, go for a camera with the ability to record a RAW file. Go for at least a 3 Megapixel camera.

• If you only take snapshots during holiday, do not be intimidated by the so called resolution of the camera. From the table above you can determine according to the print size you need, what megapixel size camera you need. If the brochure tells you the camera have a 3000x3600ppi ability, chances are that this is a interpolated resolution and not a true solution. The Megapixels are a indication of the quantity of photosites on the CCD.

• Rather go for a optical zoom than a digital zoom as far as possible. The digital zoom function can be performed on your PC as well and is not really an advantage. The optical zoom is the good one, that zoom is perfomed by the lens. Thus an enlarged image is recorded.

• Batteries are becoming un-affordable these days. If you can find a camera you like which use penlight, other standard batteries or rechargeable batteries it will be a great benefit. Even some of the modern professional digital SLR cameras like the Pentax K110D use rechargeable penlight batteries.

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