Taken from here.

For many digitisation projects the choice of digital camera will be from among the high-end professional cameras. These digital cameras, although very expensive to buy, can now offer quality equal to that available from film, within a production workflow that is easier to manage and, with a large enough throughput, can often be cheaper too.

However, many projects either do not have the budget for a high-end camera, or find that they still have a pragmatic need for 'cheap and easy' capture of a range of subjects, for which they do not need the highest quality.

For these projects, one of the vast range of low-end or consumer digital compact cameras can often provide enough quality to fulfil their needs.

The development of these digital compacts is fuelled by the consumer market, which has lead to a very fast growth in quality and functionality in the last few years. Although they are still comparably much more expensive than film cameras with roughly equal quality and functionality, the 'ease of use' and 'born digital' nature of the images makes the additional cost worthwhile for many users.

When you pick up a digital compact for the first time, you will see that, with a few exceptions, their design is largely based on their traditional film counterpart. In fact within normal use there are far more similarities between digital and traditional cameras than there are differences and it is quite easy to forget that the camera is 'digital' at all. The skills you need to get good images out of a digital camera are essentially identical to those that you need for a film camera.

This document looks at some of the common factors and skills needed for both digital and film cameras, and then looks at some of the things that make them different. Of course we don't intend to go into the individual workings of the camera, for that you will need to read the instructions.
How analogue and digital compacts are alike...

All cameras need light

All cameras, whether digital or film, rely on light to make their images and, within reason, in normal use, the more light the better. If you are trying to improve the quality of your images, then first of all make sure you have enough light.

Of course, the quality of the light will also make a fundamental difference to the look and feel of your image - although an internal flash, daylight and tungsten studio lighting all give ample light and fine quality, the resulting images will all look different. It is up to you to make a 'creative' choice as to which best represents how you want the image to look.

As a general rule, unless you have a creative reason not to, put the main light source behind you and try to avoid shooting into any bright lights (sun, window, etc.)

When lighting your subject remember that the more directly behind you the light source is, the flatter the lighting will be. The more 'side-lit' the subject is, the longer the shadows will be and the more feeling of depth will be conveyed.

If a point light source is used (sun, lamp, etc.) the shadows will be hard edged with little detail within them. However if the light source is large and broad (sky, lighting umbrella, etc.) the shadows will have soft edges.
Remember to use good basic camera skills

To get good results with any camera (digital or film) you will still have to master the same range of basic photographic skills:

* Keep the camera steady
One of the best ways to ruin your photos with any camera is to move it whilst you are taking the shot, so remember to keep the camera as still as you can. Unless you have lots of light, consider using a tripod to keep the camera stable. Using a tripod will not only make your photos sharper, but it can also help you to concentrate on the content of your image, which will lead to the shots being more reliably framed and focused.
* Remember that long (telephoto) lenses are harder to use
Long lenses give only a small angle of view, and any small movement of the camera will easily be exaggerated, possible harming the quality of the image. They also have less depth of field and are less efficient at transmitting light.

This is less of an issue for compacts than it is for SLRs, but still applies if your compact has a zoom lens. The longer the lens, the more important it becomes to make sure you have enough light, and also that you keep the camera nice and steady (preferably using a tripod).
* Problems with flash
If you can adjust the flash, make sure it is angled in such a way that the light it casts does not cause unwanted reflections, glare or shadows. Of course, if the camera uses a built-in flash you might not be able to adjust anything. On the other hand, it might still allow you to capture an image that would otherwise be impossible.
* Composition - think about what you are shooting
An old adage of professional photography states: "There are only four important things in an image - the top, bottom, and both sides." It is easy to get carried away with the excitement of what you are shooting, so always make a conscious effort to remember to look around the four edges of your image. Make sure the horizon is straight and nothing important is falling out of the image. After a while this skill becomes second nature and hopefully you will no longer take photos that cut off feet or the tops of heads.
* Be aware of the viewfinder's accuracy
With most compact cameras, checking the content of images is not made any easier by one of their most annoying features: their viewfinders are very inaccurate. This is because the viewfinder is normally offset from the lens itself and therefore cannot give a through-the-lens view. This in turn means it cannot give an accurate visual representation of the image area you are capturing, especially when shooting at a short distance from your subject (in macro-mode).

Some digital compacts overcome this problem by using a LCD screen to preview the image from the CCD, although even these have a habit of losing the outer edges of the image (showing approx 90-95%). However in most cases this is more accurate than the offset viewfinder. This problem can be overcome by using an SLR (Single Lens Reflex) type camera (also normally allowing interchangeable lenses), although they are substantially more expensive and not normally found within the typical digital compact camera.

Looking after the image once you have shot it

With a traditional analogue camera, it is important to look after the camera film both before and after you have exposed it (protecting it from light, heat and even x-rays). With a digital camera it is still imperative to protect our shot images, although it is now the memory cards that must be handled with care.

These cards (Compact Flash, SmartMedia, Sony Memory Stick, Microdrives, etc.), can all be easily damaged by magnetism, physical knocking, high frequency transmission from walkie-talkies or mobile phones, and even by the electron beam irradiation used by the US postal office to search for Anthrax!

However, without doubt the biggest danger to memory cards are the camera operators themselves. It is only too easy to mistakenly delete images before you have safely moved them onto a secure long-term storage device. It is therefore very important to establish a safe workflow that enables you to reliably back up your images from the camera.
...and how digital cameras are different

Although, as discussed above, there are more fundamental similarities between film and digital cameras, there are still some important differences:
Image area

With all cameras it is good practice to make sure that you fill your frame with your subject: there is no point in using image area if you are just going to crop it out afterwards. With a digital camera the quality (and therefore cost) is directly related to number of pixels and you really do not want to throw any away, therefore this good practice becomes an imperative demand.

Of course, you can easily crop a digital image, but a digital image does not offer the same amount of surplus quality that you have on film. Each line of pixels is important and valuable, so it is important not to shoot more than you need, only to crop it away later - all those pixels are very expensive and there is no point in paying for them if you are not going to use them.

Power

Digital cameras are crammed with electronics undertaking a vast amount of processing, which tends to drain the camera's batteries very quickly. This is particularly true with the more common CCD-based cameras, however the new generation of CMOS-based cameras undertake more processing on the chip, making them less power-hungry. For further information on CCD and CMOS see TASI's report on Digital Cameras.

Camera manufacturers are trying hard to develop cameras that are less power-hungry, whilst also developing more powerful batteries. Until this happens, there is not a great deal you can do except to buy the best and most powerful batteries you can, and to always make sure you carry spares with you. Remember that two of the biggest users of power within the camera are the LCD viewing screen and the zoom function, so if you are worried about power, it is normally best to avoid using these functions any more than you have to.

It also makes good sense to use re-chargeable NiCd (Nickel Cadmium) or NiMH (Nickel Metal Hydride) batteries - they are designed for the purpose, and will soon work out cheaper than buying normal alkaline batteries. Always charge them according to the manufacturer's instructions, as it is easy to damage them by incorrect charging.

Some cameras now take Lithium-Ion (LiON) batteries, which provide more capacity than NiMH, but are more expensive and require their own charger - while NiCd and NiMH can be bought as AA batteries, LiON AA batteries are not as yet available.

Expense and fragility

One of the biggest differences you notice immediately (even before you buy one) is just how expensive digital cameras can be. Not only that, but they are crammed full of electronics, which tend to be temperamental, unreliable and horribly fragile. However, camera design is moving fast towards providing more functionality 'on-the-chip' (mainly using CMOS image receptors), which should provide both more reliable and cheaper cameras.

No matter how cheap or robust a camera may seem, do make sure it is properly insured and fully covered by the manufacturer's guarantee. Look after cameras carefully - don't leave them anywhere wet or humid, and don't leave them in direct sunlight, in a car, or anywhere in sight of a potential thief.

Digital cameras in operation

* Shooting speed
Digital cameras are generally slower to operate than their film-based siblings. Firstly because there is often an annoying delay (or 'shutter lag') between pushing the shutter button and the camera taking the shot, and secondly because there can be a long wait between taking one shot and the next, while the camera processes and saves the image. These delays are less of an issue with newer compacts, and have already been practically removed within the more professional digital SLR cameras.
* Functionality and menus
Digital compacts tend not to have many physical switches. Most functions and controls are found within a hierarchical menu system accessible via a small LCD control screen. Although these menus often provide a lengthy list of special functions, navigation around them can be both frustrating and very time-consuming.

This can make the camera painfully slow to use as you find yourself hopelessly lost within a myriad of interlocking menu systems. Normally the length of time taken to get to grips with the menu system will be just a few weeks short of purchasing an updated model, which will of course have a completely different menu system!

Special skills required for digital compacts

* Shutter lag
As mentioned above, shutter lag is an effect common with older and cheaper digital compact cameras, where there is found to be a delay between the shutter button being pushed and the shot being taken. The effects of shutter lag can be very annoying, especially if you are shooting a moving subject, but there are a few things you can do to help minimise the delay.

Shutter lag occurs while the camera is focussing, setting white balance and exposure metering, so if you can set some of these functions before you push the button, you should reduce the lag. Most cameras will pre-focus if you depress the shutter button halfway.

Once you have got used to the way your camera works, you can try to pre-empt shutter lag and push the button just before you want the picture to be taken, although this is still pretty hit-and-miss. Luckily technical advances in digital cameras will hopefully soon make shutter lag a thing of the past, but at the present, this is certainly something that should be considered when deciding which model of compact to buy.

* White balance
All cameras (film and digital) attempt to give an honest and objective interpretation of the colour they see in front of them. However, in reality the colours of everything we see are continually changing depending upon the colour temperature of the light that is illuminating them.

When we see these things with our eyes, our brains do a fine job in hiding the differences and providing colours which our brain 'knows' are right (so white paper appears white even if we are viewing it under candle light - when it is in reality bright orange).

With a film camera this effect can be counteracted by either choosing film that is optimised for a particular type of light (such as Tungsten balanced film for use under film lighting), or by making changes to the colours of the print when it is printed.

With a digital camera we can of course always correct the colour of the image after we have shot it during image optimisation, but it is much better to make sure that the colours are as correct as we can make them before we start.

This is done by establishing the 'white balance' or 'doing the greys'. In both cases this means pointing the camera at something white or grey, which allows the camera to read the colour of the light it sees and neutralise it to a white or grey, thereby correcting all the other colours at the same time.

* Compression
There was a time when computer memory was very expensive. Indeed, with early digital cameras one of the main production costs was the memory used to store the images within the camera. This led to camera manufacturers trying to cram as many images as possible onto the expensive memory cards. To do this they had to use quite heavy JPEG compression, which unfortunately tended to have a rather detrimental effect on image quality.

Most digital compacts are better these days, providing a better quality file at a slightly larger file size. But on the whole, the biggest single reason for low quality in images from digital compacts is the over-zealous use of JPEG compression.

There are three possible ways around this:

1. If the camera allows you (and you have enough space on your memory card) save the image as an uncompressed TIFF file. This will preserve all the original image information and is the best option if you want the finest quality. There are a few snags though: it uses up storage space much quicker; processing and saving that amount of data takes much longer giving slower operation; only the more expensive models allow you to do this.

2. Some cameras, again the more expensive and newest, allow you to save the image data in the raw form in which it was captured. This gives you all the image quality (exactly as it was captured) but with a smaller file size than TIFF. You can then use the RAW file at a later date to make your TIFF file. This approach is commonly available amongst the more professional digital SLRs, but is expected to become an option amongst compacts shortly.

One snag with this approach is that you cannot view or use this file (which is at this stage in a proprietary form) until you have processed it and created (by interpolation) the full image file within a standard file format. Of course best practice would still suggest that you should archive the image in a non-proprietary format such as TIFF.

3. Most cameras allow you to choose from a range of quality/compression levels when you shoot. Remember that compression will allow you to store more images but will also throw away your image quality, so use with care.

Image management

One of the fundamental differences between digital and film cameras is caused by the form the created images take. A film camera gives you some form of physical 'real-world' image (e.g. print, transparency, negative), while a digital camera creates a virtual image that does not physically exist (until it is outputted to print or monitor).

This difference has implications when it comes to image management. Physical 'real world' images can be stored easily in physical 'real world' containers but a digital image must be stored within some 'virtual' container, which is much harder to visualise and organise. It is important for physical images to be carefully indexed and filed, but for the digital images it is not only important but absolutely imperative if you are ever going to be able to find the 'virtual' images from the depths of your hard-drives. Your ability to find any image once it has been removed from the camera will depend almost entirely on the metadata that you record for it.

In its most rudimentary form the metadata may simply be the filename given to each image. If the file naming system you choose is of the descriptive kind (see TASI's File Naming document for further information), the filename alone may provide enough information to navigate around a small collection of images. However, additional metadata becomes key (while the filename takes on less significance) once the images are stored in an image management system.

Most digital compact cameras now automatically capture a range of useful metadata within the image as it is created. Technical details, such as the time the shot was taken, exposure settings, camera make and lens information, can be automatically collated and stored within EXIF (EXchangeable Image File) 'tags' on the header of the image file itself. Further information can also be held within a similar range of tagged metadata fields defined by the IPTC (International Press and Telecommunications Council).

This approach to storing metadata might appear to be the answer to the problem of identifying images, however, as ever there are problems with this approach. It is unwise to rely on image tags alone - while some applications may fully support EXIF and IPTC data, others do not. More importantly, tags can be wiped completely if an image is opened and saved in a non-supporting program.

Conclusion

Digital compact cameras are getting cheaper by the day, and advances in camera technology are giving us gains in quality and functionality. Providing you are clear about your project's requirements, and use the guidelines outlined here, getting to grips with a digital compact should be quick and easy.

Although it is common knowledge that the high-end professional digital camera can easily provide quality on a par with traditional film cameras, it is also evident that a digital compact camera, if used correctly, can provide easy and pragmatic capture of digital images at an acceptable cost. The quality will not match what is available from high-end cameras, but will often provide an image of sufficient quality for many uses.