Digital Images
There are four most common image files which are used in Web Design today, these being ? JPEG, GIF, TIFF and PNG. These image files have their own individual ways of storing colour modes. A JPEG image using RGB mode will store 24 bits per pixel or 8 bits per pixel in Grayscale mode. A GIF image file provides indexed colour at 1 or 8 bits per pixel. A TIFF image using RGB mode will store 24 or 48 bits per pixel or 8 or 16 bits in grayscale mode and at indexed colour holds 1 or 8 bits per pixel. A PNG image file using RGB mode will store 24 or 48 bits, grayscale 8 or 16 bits and indexed colour 1 or 8 bits.
Photographic images usually have continuous tones within the image, this means that pixels that are positioned close together usually have similar colours, and for example, a photo of green grass will contain numerous shades of green. A JPEG photographic image is usually 24-bit RGB colour, or 8 bit grayscale, and a typical colour photograph may contain around 100,000 colours, out of the possible set of 16 million colours in 24-bit RGB colour.
Website Design UK pages require JPG, GIF or PNG image types, because that is all that online browsers can show. JPG is the best choice on the web for photo images as it is the smallest sized file and website pages tend to use the GIF format for any graphic images e.g. logos or line art.
Graphic images do not normally have a continuous tone unless a gradient has been used within the graphic. Graphics are drawings are not like photos plus they usually use few colours, less than 16 colours in the whole image. In a colour graphic cartoon, a particular area of colour will use one shade, where as in a photograph there may be numerous shades of one colour. A map is produced using graphics and only uses 4 - 5 map colours plus 1 - 2 colours of text and then blue water and white paper, so these types of graphics use less than 16 colours, Graphics like this are ideal for Indexed Colour.
The TIFF file format is the best image file to use when best quality is required, and this is why the TIFF is common in professional, commercial printing environments and for Web Design England. High Quality large JPG images are also good too, but they can be ruined if they are made too small.
The 2D digital image is split into two parts, images know as ?bitmapped? are usually used in image making programmes such as Photoshop or painting packages, bitmap images are usually made up of rectangle picture elements known as pixels and each pixel is a colour, if the image is enlarged you can see these pixels and the image appears jagged, this can be improved by increasing the number of pixels per inch, known as a higher resolution image.
The other part is known as a ?vector? image and these are used in drawing and illustration programmes like Adobe Illustrator, a vector image is made up using lines and shapes, if the vector image is enlarged the quality will not degrade and the smoothness of the final image is only determined by the output device used to print the image.
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