When registering a picture you will be given the option of reducing the file size with the default being that it will be reduced. This page explains why.
You can find more on image file formats and sizes here.
For the time being SpaceForMyArt only accepts JPEG images.
You can find out more about the image formats at Wikipedia. JPEG is the most popular image file format and is supported by most, if not all, cameras and scanners and so you shouldn't have any problem generating the format. If you can't generate a JPEG format for your file it is possible to change it using other software packages. If you are still having difficulty contact Simon.
The reason JPEG files have become the standard for the web is that even relatively small ones, have an acceptable quality and resolution for viewing on screen. However, when they are downloaded and enlarged for printing the image is of low quality. This helps to protect your copyright.
When a file comes out of the camera or scanner it is very large, typical 5MByte (5 Mega Byte) or larger. Whilst this file size is needed for photographic prints when being placed on the web it has two problems:
As mentioned above when a visitor views a picture they can download it and it will be the same size as the orginal. This means that they can reproduce it as a high quality print . Downloading the image is very easy, most browsers just allow you to right click the image and give an option to download.
You could provide a watercolour copyright on the image if you have a suitable package, but that will spoil your visitors' enjoyment of your pictures and website.
Large files can spoil the visitors experience by making them wait for long periods while the image is downloaded, especially if they have a slow Internet connection, with no real benefit in seeing a better image on screen. The experience is made worse if the page contains multiple large images because they download simultaneously and in no particular order.
To give you an idea of how long it can take, and without using too much jargon:
A typical internet speed claims to be 2Mb (2,000,000 bits per second), in reality the user is lucky to get 500kb (500,000 bits per second) on average and may be slower in busy periods. It should be noted that these speeds include all the overhead information needed to control the download as well as any other management and application data, but for this explanation the overhead data will be ignored for ease of calculation.
A typical picture from a modern compact camera will be around 8MByte (8,000,000 bytes) and 1 byte = 8 bits ie it will be 64,000,000 bits in size. So at a download speed of 500,000 bits per second it will take:
Download time (Full size) = 64,000,000/500,000 = 128 seconds at 500kbps download speed and 32 seconds at 2Mbps download speed.
Whilst this may be just about acceptable for 1 picture on the main screen the viewer could be waiting for 9 pictures to download.
In comparison, this programme can reduce this typical file to around 180kB, depending on the richness of the picture. This file will take:
Download time (File size reduced) = 180,000/500 = 0.36 seconds at 500kbps download and 0.09 seconds at 2Mbps download speed.
To fully understand this you need to understand pixels, pixel(colour) depth and screen resolution. However, in brief a typical large computer screen is around 1600 x 1200 pixels, but much smaller for laptops, and not always used at that size anyway.
A typical photograph direct from a modern compact camera will be around 4,000 x 3,000 pixels.
This programme scales the picture to a maximum of 1200 pixels wide or 800 pixels high, depending on the image orientation.
This doesn't mean you lose information from the edge, it means you lose detail evenly across the whole picture. This isn't normally noticed on screen because your visitors will see the picture scaled, without loss of detail, to a maximum of 800 pixels wide or 600 pixels high, depending on the image orientation. Where it may be noticeable is if your visitor zooms in to look at fine detail.
Here is an example using one of Sue Fawthrop's Durdle Door pictures.
The original file is 4.9MB and 3,276 x 2213 pixels and has been constrained to a size of 800 x 540 for on screen display. You may have noticed it downloading slowly when you opened this page.
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This version has had its file size reduced to 171kB by scaling it to 1200 x 800 pixels. It has then been constrained to 800x 600 pixels for display.
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As you can see there is little, if any, difference to the naked eye between the two pictures, but the user will have a much better experience viewing your poictures and navigating around your website. For this reason the default is is file size reduction when you register a picture.