Chapter 2 - How to Do
This
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| Chapter 2 -- How
to Do This It goes on to describe how to add value to images for educational purposes looking at enhancing, highlighting, and labelling. The choice of appropriate image file types is discussed, with links to more detailed material. Downloadable worksheets, template
and example files are provided for further learning. |
2.05 - Image file formatsThe need for compressionWeb pages and their image information need to be as small as possible because they need to travel over networks and telephone lines which can be slow. As a result of this, the image file types in use for Internet pages use different ways of compressing the image data.
File types in current useAlthough there are several interesting and potentially useful new file types in the pipeline, there are only two in current common use.
Choosing the right file typeWithout going into unnecessary complexity, GIF's are good for relatively simple graphics and diagrams -- especially those which have large areas of uniform colour. The top image on the right would compress well as a GIF. This map from the Mapping Social Capital tutorial shows limited numbers of colours and large blocks of uniform colour. The JPEG format is best for photorealistic images
and those with colour gradients. The image on the right would compress well as a JPEG. This photorealistic image from the Biomed image archive has multiple colours and gradients. Compression softwareThere are a number of software packages available -- (Macromedia FireworksTM is one which I use). These packages facilitate the alteration of detailed image parameters to reduce file size without causing unacceptable deterioration in appearance. The automation built into these packages which reduces the number of decisions that have to be made is also excellent. Once I have an image with which I am satisfied, it usually only takes me 20 seconds or less to export it at an optimum size. Page file sizeIn terms of attracting the surfer, collective wisdom says that a page file (including its images) should be less than 40 kB. However this comes from research involving the use of the Web as a sales medium. When providing learning material for students who are committed to the learning process, I believe we can afford to tolerate larger page sizes. This should not be a licence to kill students with boredom as they wait for pages to load! Page design can improve the situation by engaging the student with material to read and see while the remainder of the page loads -- preferably in an invisible way. This is one of the design criteria for this work. Finally, if the student must wait for large images to download, describe the image in the ALT text so they have some idea of what they are about to see. You should be doing this for accessibility reasons in any case. Link to more information There is much more useful information on image file formats at the |
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Using Images in E-learning
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