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Article: Cameraphone Photography

Introduction

There was a time when not everyone had a camera at their disposal. Certainly back in the 70's and 80's this was the case. This was the era of the 126 and 110 compact cartridge cameras. These cameras, specifically the 110 format, captured images on very small negatives. The image quality was often derided as the quality was at best seemed as only suitable for snapshots. There were attempts to introduce higher quality cameras for the format but in the end the format made way for 35mm compacts.

The initial introduction of cameras on phones was derided by some as pointless as they used tiny image sensors and were initially separate modules that had to be attached to the phone and offer a very limited image resolution of only 1/3 megapixel (or VGA at best) with only fixed focus. It did not help that LCD screens on the phones at that time were also poor in resolution and colour rendition. However with each generation of phone there has been significant improvements in the technology to permit cameras to be built into the phones and the LCD screens offering ever increasing resolution and colours more colours than the eye can perceive.

The mobile phone has become part of everyday life and the fact that most phones now have cameras built in means there is less chance on missing a photo opportunity whether at a social event or just out for a walk.

The Features

Digital cameras have been offering increasing megapixel count with nearly every generate. Despite the tiny image sensors used camera phones have not been exceptions to this rule. Currently top end camera phones offer resolutions up to 8 megapixels but this will be increase to 12 megapixel by the end of the year (2009). Unfortunately there are severe limitations that act against the benefits of the increased pixel count. The Imaging sensor in the typical compact digital camera is measures around 1/2" (diagonal). By comparison the typical sensor used in a camera phone is even smaller, measuring 1/4". As the physical size of a pixel reduces its ability to collect light also declines. The reduction in captured light means the digital representation drops in amplitude bringing it closer to the noise floor (as dictated by component and general system noise) making image noise more obvious. Sophisticated image processing is the order of the day with all digital cameras but with camera phones more effort is required to keep image noise under control. Strong noise reduction helps but at the same time introduces artifacts which will likely make the final image look artificial. A compromise has to be made between image noise levels and final image quality. The camera phone has not been designed to tackle demanding photographic situations but for casual use.

Despite the limitations of current camera phones their use is increasing with some people using it as their main camera whilst on holiday. No doubt as use increases there will be more demands for improved image quality. The low end low budget compact digital camera may be consigned to the history books. 

The features provided within camera phones are expanding. Although you won't find full manual exposure control (or even aperture priority for that matter) a number of controls are increasingly being provided to give added flexibility. The features you can typically expect are as follows:

  • Exposure Compensation
  • White Balance
  • Metering mode
  • Flash (Xenon or LED)
  • Focus Mode
  • Focus aid light
  • Timer Standby
  • Digital zoom
  • Face Detection
  • High quality LCD or AMOLED screen

The main missing feature is optical zoom but the phone size is no doubt the constraining factor here.

Autofocus

Very few camera phones are fixed focus now. The implementation of autofocus varies from camera to camera. Some show a discrete focusing point where others may not show a focus point at all and use any part of the screen to focus with a particular focusing bias towards the central area. The more recent AF systems are now employing face detection to minimise the occurrence of mis-focus when attempting to take a portrait of someone. With the growing popularity of touch screen phones, touch focus has been introduced as a quicker way of specifying where the camera should focus. 

The Flash System

Just like the digital compact cameras, the flash systems on camera phones have a tendencyCameraphone Xenon Flash to be under powered and as a result provide only sufficient illumination for close subjects. This may not be an issue if all you are taking is portraits of people (mainly head and shoulder shots) but full length shots may be a struggle for the flash system due to the extra distance.

There are generally two types of flash systems employed on camera phones; the Xenon flash, and the LED flash. The Xenon flash is as close to what is employed on standard cameras. It produced a very brief but intense flash of light. The LED flash on the over hand produces a bright light of longer duration. Most modern camera phones will feature dual LED flash system as a single LED flash provides very short range illumination. Doubling up the LEDs increases the overall brightness in an attempt to match the xenon flash systems.

Cameraphone LED FlashAssuming parity between the Xenon and LED flash systems there are significant differences that affect how best the flash can be used. The xenon flash with it's very brief but intense light output provides a means of freezing any subject motion. The flash light only has a during of say 50µs. The LED flash on the other hand cannot produce such a short duration of light (shortest duration typically in milliseconds rather than microseconds). As a result should the subject move it is likely the resultant image would be blurred even though illuminated. The LED flash does have the benefit that it can make a decent video light as it can produce a continuous light source (where as the xenon flash cannot). Some cameras have been known to employ both systems but the LED flash is the system mostly used.

 

Taking Photos

With the various elements that conspire to degrade image quality the camera phone is still capable of taking acceptable quality photos in the right conditions. As with any camera, it is important to use the correct settings to ensure the best quality.

All camera phones are storing their images in the JPEG format. Image compression has an obvious effect on the final quality of the image. If memory space is not an issue (and it should not be if images are saved to a memory card rather than the phones internal memory) and there is a facility to adjust the quality level, then it should be set to its highest setting. This represents the least amount of compression that the camera phone will allow. The effects of data compression are unlikely to be obvious when just viewing a captured image on the phones screen (with the whole image displayed) but magnifying the images and the artifacts become apparent. If prints are intended then the highest quality setting is a must.

With no aperture or shutter speed adjustments to be concerned about the user can just concentrate on getting the right composition. The camera phones responsiveness (or in many cases the lack of) can dampens a persons enthusiasm for taking photos. The shutter release on the typical camera phone is not responsive. Pressing the shutter half way to achieve a focus lock can be slow and then the response to pressing the shutter all the way down to make the exposure seems to impose another delay. If the subject remains still or is not likely to be going anywhere (i.e. a landscape) then slow autofocus and camera response may not be an issue. Sports on the other hand become more of a challenge. By the time the camera phone has focused and released the shutter the sports subject may be long gone. Some phones provide a facility to set the AF to infinity. With a camera phones typical wide depth of field the infinite setting effectively means subjects will be sharp from about 3 metres and beyond. With the focus fixed there is no pre-focus delay time which makes the phone feel that bit more responsive.

Depth of field is not an issue unless the subject is especially close to the camera. It comes into play when taking macro photos and can add a bit of dimension to the overall photo.

As the focusing system is using the contrast level presented on the image sensor, if light levels are too high focus errors may happen resulting in blurry images. Sometimes it is useful to focus on a different part of a subject (at a similar distance) to ensure good focus.

The exposure metering is usually linked to where the focus is. There is very little that can be done here. Exposure compensation if available should be applied where necessary (either for a better exposure or as a form of special effect).

All camera phones will automatically try to determine the correct white balance. On the whole they do a respectable job but they can be fooled. If preset white balance settings are available they should be used to ensure a more consistent set of results across a set of images.

The JPEG image files are always sharpened. Unfortunately some are over sharpened but this is to be expected for a camera that is aimed at the general consumer. It does mean that decent prints should be possible without any further user intervention.

At the end of the day, the camera phone is all about fun and having a method of recording those unexpected events at any time. With more phones now having GPS modules built in it is possible to geotag images so the location a photo was taken will never be forgotten.

 

Mini News

22 November 2012: Sigma 18-250mm now available in Sony's A-Mount

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17 October 2012: Firmware update for Sony NEX 7 v1.01

Sony NEX firmware update provides the following;

  • Addition of capability to enable or disable the MOVIE button
  • Addition of exposure settings of bracket shooting (three frames /1.0EV,2.0EV, 3.0EV)
  • Improvement of response for showing auto review image.
  • Improvement of image quality when using a wide angle lens
  • Improvement of indication when setting “Flexible Spot”.

Visit the link: http://www.sony.co.uk/support/en/product/NEX-7/updates

Firmware updates are also available for the a77, a65, and a57.

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