image construction

see also about JPG files

Picture elements - known as pixels


Digital pictures consist of small square elements called pixels

Perhaps the easiest way to consider a digital image is to think of a tapestry, made up from thousands of stitches, in a digital image these are called 'pixels'

The temple picture used 6 million pixels in the original from a digital camera

This version modified for the web has only 26,000 which is plenty for the size shown

Each pixel has an individual colour stored by the computer
This star and crescent is a 100x100 pixel section from the top of the central minaret in the original picture This is a further magnification showing just the star. The square pixels can now be seen. Digital manipulation allows a single pixel to have it's colour changed, in this case to pink! An even greater magnification shows the detail

colour
Computer screens rely on a varying mix of red , green and blue to derive the wide range of different colours required to make a picture
Magazines and other printed items using traditional methods use 4 inks - cyan , magenta , yellow and 'black'

Pictures produced by digital cameras and printed on an inkjet printer typically use RGB which can resolve a slightly wider range of colours than CMYK

Digital manipulation programs can convert from RGB to CMYK and back again. However once a picture has lost some colour detail when converting from RGB to CMYK it cannot be recovered

At the we use RGB with it's wider gamut unless requested by the client

resolution


This term is used to describe the number of pixels in a digital image

To produce high quality printed pictures, the digital file must have the necessary pixels and not be a heavily compressed .jpg file - to see how many you can get on a CD-ROM

Programs which indicate the size of a picture as inches or cm rely on the pixels/inch stored in the file

For high quality magazine printing, the usual standard is 300dpi (dots per inch)


To produce a good picture 1" square in National Geographic requires a computer file of 300x300 pixels since each pixel becomes one dot in the printing process

Computer screens are usually 72 or 96 pixels per inch

The same 1" square image requires less than 100x100 pixels for screen use

If a digital picture is 3000 pixels wide it should be possible to reproduce it in any size up to 10" wide on paper - if it is printed larger the quality will decline as the result is made bigger

Digital manipulation programs can both reduce and increase the number of pixels in an image BUT if the number is reduced the real resolution cannot be regained unless a copy of the original picture is used.

(Programs which increase the number of pixels in an image always make some kind of approximation)

At the we use the best standard off the camera unless requested by the client