Microsoft Active Server Pages is a programming language that works on a Windows webserver.

Amongst other things it allows information from a database to be added to a webpage.

Information you submit from a webpage can also be added to a database with ASP.

On Linux servers a language called php performs the same function.

There are three types of colour receptors (cones) in the retina of the human eye, each receptive to a different frequency range of light; broadly red, green, and blue (the primary colours).

Television and computer screens utilise this fact and transmit only three colours, each intended to stimulate a particular cone type.

A computer screen can transmit 256 different intensities of each of the three primary colours. In this way it is possible for each pixel on a computer screen to display any one of 16,777,216 different colours (256 x 256 x 256).

HTML and cascading style sheets describe colours using hex.

You can mix any one of the 16,777,216 colours here.

Enter your own values for red, green and blue to mix a colour.

Red Green Blue

Cascading style sheets are generally used to catalogue the various styles of text required on a website.

The style can define the font name, colour, size and weight used for a particular area of text, amoungst other things.

Each style is given a unique name which the HTML can refer to whenever that style is required.

Dithering generally occures in image formats with a fixed or limited range of colours, for example a GIF.

If an area of an image contains a colour that is not available (e.g. a colour not included in the palette of a GIF) the colour is "dithered" between two or more colours that are available.

Dithered and undithered images magnified. The dithered image is on the left.

Every website on the internet has a unique address; in the case of this site, someonelocal.co.uk.

This is often referred to as a URL (Uniform Resource Locator).

In the context of website hosting, it is generally called a domain.

In other words, someonelocal.co.uk is a web address, a URL, and a domain. They all refer to the same thing.

When you visit a website, files are downloaded from a webserver to your PC. You may also have the option to download additional files.

Most internet traffic involves downloading. See upload

Website layout falls into two categories - fixed-width and fluid.

As the name implies, a webpage with a fixed-width layout stays the same regardless of screen resolution or size of the web browser window.

This has the advantage of making pages predictable, and allows you to place the web content in exact positions on the page.

The main disadvantage of a fixed-width layout is that one size does not fit all.

If a page is made narrow enough to display properly on a low-resolution screen, it will have large unused spaces to one or both sides of the content when viewed on a higher resolution screen.

If the page is made wide enough to display well on high-resolution screen, it will produce a horizontal scroll bar on low-resolution screens.

Because fixed-width pages do not expand to fill the width of a page, they tend to be taller, and require a bigger vertical scroll bar than a fluid-layout page with the same content.

Website layout falls into two categories - fixed-width and fluid.

Fluid-layout webpages stretch and contract to fit the size of the web-browser window, and need less horizontal or vertical scrolling than fixed-width pages to view the full content of the page.

The elements of a fluid page are given relative positions, rather than absolute coordinates.

Some web-design software is not able to create this kind of layout

File Transfer Protocol. This language is used to transfer files from a PC to a webserver, also known as uploading files.

Files are downloaded to your PC using another languge, http

Graphics Interchange Format

This image format is restricted to a maximum of 256 colours, optionally including one transparent colour which allows any background image or colour to show through the transparent pixels.

The actual colours used are defined in a palette held within the GIF.

GIFs are generally preferred to JPEGs for simple images involving few colours, such as logos and text, as they are lossless.

JPEG rendering of this type of image can introduce "smudges" by its lossy compression.

The GIF format also supports animation, where several frames are stored within an image and displayed sequentially.

Short for hexadecimal, meaning base-16. It is mostly used on the internet to describe colours.

A hexadecimal character has a value between 0 and 15. Values 0 to 9 are the same as in decimal, 10 to 15 use letters (A = 10, B = 11, C = 12, D = 13, E = 14, F = 15)

A two character hexadecimal number can have a value anywhere between 0 and 255 (the left hand character represents multiples of 16, the right hand character multiples of 1). So 'FF' represents 255, i.e. 15x16 + 15x1.

The colours on a computer screen also use the range 0 to 255.

Each primary colour (red, green and blue) can have an intensity between 0 and 255, with 255 being maximum brightness.

On the internet colours are described using two characters of hex for the intensity of each primary colour. The format is '#RRGGBB' (# here means hex. RR = Red, GG = Green, BB = Blue).

Here are a few examples of hex codes for colour...
small = #000000
business = #1810CC
websites = #882288

For a website to be available on the internet it needs to exist on a webserver.

This is called hosting. The webserver hosts the website.

Hypertext Markup Language. This is a very extravagent name for the language used to create web pages.

Hypertext is intended to imply that the text is more than just words, it can contain links to other webpages and information about how the page should be displayed for example.

Any images on a webpage remain as separate files. They are downloaded and arranged on your screen by your web browser according to the instructions of the HTML.

Hypertext Transfer Protocol. This is the language used when you download webpages from a webserver.

This is generally included as the first part of the address when you visit a website, e.g. "http://www.someonelocal.co.uk/help.htm".

Web developers use a different language for transfering files from a PC to a webserver, i.e. uploading. see FTP.

Javascript is a language that enables web developers to add functionality to webpages. Javascript can make changes to a page you are viewing without having to refresh the page from the webserver.

If you have Javascript enabled and you hover your mouse here, the word will turn red. This is done using Javascript.

The effect of an image or text changing when the mouse hovers over it is often called a rollover.

Joint Photographic Experts Group

This format is almost universally preferred for photographic images. There are no restrictions on the number of colours used, unlike the GIF, and it is more compact than a PNG.

The format is lossy, but if the level of compression is controlled properly the loss of acuracy is not generally noticable for photographic images.

There are two types of webserver, Microsoft Windows and Linux.

The type of webserver makes no difference to the visitor of a website. In fact, most people run Windows on their computers, but most webservers run Linux.

Windows webservers use ASP as the language for developing advanced webpages, Linus webservers use php

This website is running on a Linux webserver.

An image saved in a lossy format, such as a JPEG, may not retain the original colour of every pixel. This form of compression is designed to reduce the file size of photographic images. Providing moderate compression is used the loss of quality is not noticable.

Lossless compression retains the exact colour of each pixel, and only reduces file size by using short-hand to refer to repeated sequences of pixels. Photographs saved in this format take more space. One lossless format, the GIF, is restricted to 256 colours and unsuitable for most photographs.

Very simple images, such as text, saved in JPEG format may show a noticable loss of definition, and produce effects like "smudging".

A magnified JPEG image showing "smudged" grey pixels on what should be a pure white background.

In the same way that ASP is used on a Windows webserver to interact with databases etc., php is used on Linux webservers.

It is a powerful, flexible language that allows web developers to do far more than is possible with HTML alone.

The word pixel is used in a number of ways, but always refers to a tiny segment of an image, and is always a single colour.

A computer screen is made up of regular dots of each of the three primary colours - red, green and blue. These are sometimes referred to as pixels, particularly when describing faulty dots that don't light up, i.e. "dead pixels", but are better thought of as sub-pixels.

On a screen a pixel is a collection of neighbouring sub-pixels, with at least one sub-pixel of each of the colours.

Depending on it's screen resolution a monitor may typically display a grid of between 480,000 pixels (800x600) and 1,310,720 pixels (1280x1024) or more.

A digital photograph or image is similarly made of a grid of pixels.

An image or text is said to be pixalated when the pixels it is made of are too obvious. This can happen for a number of reasons.

A common cause is a lack of mid-tones. Even a black shape on a white background will require grey pixels at its edge to appear smooth.

A JPEG saved with too much compression may lose mid-tones to compress the image.

An image with many colours saved as a GIF will lose mid-tones, as a GIF can only have 256 colours. A GIF can also suffer pixelation due to dithering.

Some images may be deliberately pixelated to avoid showing detail.

Portable Network Graphic. This image format has advantages over both JPEGs and GIFs.

The JPEG is lossy and the GIF is restricted to 256 colours.

The PNG is not lossy, or restricted to a fixed number of colours. It is, however, often larger than equivalent JPEG and GIF images.

The term rollover is used to describe text or images changing when the mouse hovers over them.

If you hover your mouse over the green pointer for a few seconds it should change to a red pointer, then return to green when you move the mouse away.

A computer screen is made up of a fixed number of regular dots of each of the three primary colours - red, green and blue.

Each coloured dot is called a sub-pixel, and in turn is part of a pixel.

Pixels are always arranged in a regular grid of rows and columns, but the actual number of rows and columns can be altered by the user. This is called the screen resolution.

As each pixel must contain at least one sub-pixel of each colour, the highest screen resolution available on any particular screen is determined by the number of sub-pixels it has for each colour

Your screen resolution is currently x (columns x rows)

Your screen contains a total of  pixels.

When files are copied from a PC to a webserver they are uploaded. This is a common part of web development.

Sites are generally created on someone's computer and then copied up to a webserver to make them available on the internet. See download

A web browser is software that can request and send files between the machine it resides on and other computers connected through the internet, typically webservers.

It can construct webpages by reading code written in HTML and displaying words and images as instructed by the code.

Standards define how a web browser should interpret HTML, though some follow the standards more closely than others, and different web browsers may use different default values for settings where none are defined in the HTML.

Web browsers include...

Internet Explorer	Firefox	Netscape	Safari	Opera

A webserver is a computer that is always connected to the internet and runs software that allows it to respond to requests to view websites.

A webserver can host many websites, and control the space and traffic allocated to each separately.

Most webservers run on one of two types of computer, those running Apache on Linu servers, and those running Microsoft Internet Information Services on Microsoft Windows servers.

The type of webserver used makes no difference to people visiting the site.

A website is one or more webpages. To be accessed from the internet the website needs to be hosted on a webserver.

Each webpage is a page of HTML plus any other files that are required to render the page.

These files include images, such as JPEGs and GIFs, as well as cascading style sheets (CSS), and Javascript.