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Compression & File ShrinkingThis tutorial will guide you through some of the many different methods of reducing your images and other documents in file size making it easier to send via email and distribute using the Internet. Image Compression Jpeg saved at 80% compression, 28k  Jpeg saved at 60% compression, 16k .jpg) Jpeg saved at 20% compression, 7k  GIF saved with 256 colour's, 36k  GIF saved with 64 colour's, 21k  GIF saved with 8 colour's, 9k Jpeg is the most widely used image compression technique, but depending on your original image, it may not be the most suitable. The jpeg compression is best used for colour or grayscale photographs or images which can be described as real life or high in detail, such as a photograph of a landscape or your family and friends, the jpeg compression isn't really suitable for cartoons, outline drawings or images with a small number of colour's - such as text. It works by splitting you image into a grid, each pixel within each smaller grid is then converted into numbers, and it is the relationship between these pixel numbers that is saved. So the closer the colour's of 2 adjacent pixels, the smaller the relationship and therefore the smaller the file size. You can adjust the level of compression when saving (or exporting as a) jpeg and this reduces the gap between adjacent pixels in colour, so if you compress an image by a lot, the result can look blurred, which the example on the right demonstrates, as the compression gets lower, the file size also reduces, but so does the quality of the image. When saving a jpeg you need to decide what is important, the file size or the quality of the final image, it is also important to know how you are going to use the image, this will help you choose what level of compression to use. If you intend to make additional edits / changes to an image then you need to save it with the best possible quality, because each time you edit and save a jpeg, the image will deteriorate. There are some very good free applications that will allow you to resize, crop and save jpegs, here are just a couple; • Irfan View [www.irfanview.com] You can of course use Adobe Photoshop, PaintshopPro and any other image editor. The gif file format is perfect for images that don't have many colour's - such as graphics, cartoons or plain text. A GIF (Graphics Interchange Format) is a bitmap format that is restricted to only 256 colour's from the palette of 16.5 million colour's available to a 24bit image. Because a gif will only use 256 colour's, they are unsuitable for photographs and other images with large amounts of colour and detail, such as the example on the right. Gif's are commonly used for logo's and design elements within website's where images used sharp lines, and are of limited colour. Gif's also have a transparent attribute, where any colour within the pallet of 256 colour's (or less) can be turned transparent. Finally, gif's can also be animated, by building up a series of frames, a file can cycle through these frames to create a animation or movie which can be displayed on a web page or within the body of an email. Gif's are saved by listing each pixel used in the image, from the top left hand corner in rows reading from left to right. This is also how bitmaps are saved, but gif's work slightly differently as when 2 or more pixels adjacent are the exact same colour, then they are listed as 2 x red instead of red red, or 5 x blue instead of blue blue blue blue blue. So this will dramatically reduce the file size as less information is having to be saved. Both the programs featured above will save gif's. File CompressionCompressing or zipping up a file will, depending on the type of file, reduce the size dramatically and make it far more efficient to send via the Internet and email.
An A4 300dpi bitmap image of the beach scene above is approximately 25mb, but compressed as a zip the file size is reduced to approximately 11.5mb. The same image saved as a jpeg with the maximum quality - so very little compression, is just 2.5mb, but when 'zipped up' the file is only reduced down to 2.4mb as saving it as a jpeg has already reduced the file size considerably, using it's own compression method. More Tutorials
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Windows XP now comes with file compression built in, previously you would of needed a program such as winzip to create zip files. Within the Windows environment, right click on the file that you want to compress and select 'add to compressed folder' this will place your selected file in a compressed folder with the file extension .zip.