Pixels and photography

Camcorder / Digital Still Photography - Gordon Sutton

Many digital video cameras now have the capability to double up as digital still cameras (DSCs) with the images being stored on a removable memory card. Two types of still images are therefore possible from video cameras - those from tape and those from an image card. Older cameras with cards capture 640 x 480 pixels (light sensitive picture elements) so better stills were available from dv tape which has 720 x 568 (408,960 pixels per frame). In modern DV cameras there are more image sensors on the charged couple device (CCD) than are used to generate the video image so card stills are now better than tape stills. A typical miniDV video camera has a 1/4 inch sensor with a possible moving image pixel count of 690,000. On cameras with electronic stabilisation, the extra pixels are used in the stabilisation process. The still image capability however, can now be in excess of 1 mega pixel. In effect, the higher the number of pixels the larger the size of print which can be made before blurriness/pixelation degrades picture quality too much. Images from cameras with 1 to 2 mega pixel start to improve dramatically but the image will still look a little course and nowhere as good as even a throwaway film camera. Image sensor; with more than 2 mega pixels start to give near photo quality results. For a sensor with more than mega pixels it will be difficult to tell the difference from those shot on photographic film. The number of picture elements or pixels that make up a picture are measured in dots per inch (dpi) - 72dpi is enough for web images / documents and 300 dpi plus for good photographic prints. A lot also depends on your printer and you won’t go far wrong with models with at leas 2400 dpi A USB cable is the likely means for the transfer of digital stills from the camera to the PC. The alternative is to use a card reader that allows the PC to treat the card as an extra hard disc drive (it’s much faster and saves socket wear and battery power). A multi-format memory card be reader is regarded as a good buy and can be from many web sites at around £20, and gives you the option of accommodating six different types of cards. When zooming, stick to using the optical range only. In camera digital zooms, although apparently impressive in number terms, simply enlarge the image electronically and therefore have a degrading effect on quality. Get in close if you want the object larger. Similarly, its well worth capturing still images at the highest possible resolution to give maximum choice of use afterwards. You can always reduce the file size in a copy of your original for email purposes, but you can’t put back lost detail. Most cameras save in JPEG format on their image cards, which gives the smallest file size. Every time you save an image in JPEG format you degrade the picture a little because JPEG throws away information to keep the file size down. It is better, therefore, to copy the JPEG file image onto the PC and keep it unchanged as the original. Save any changes you might make to a loss less format like BMP, TIF or PSD from then on that way best quality is preserved.