Webquest

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Webquest

  1. 1. Webquest Katie Greenhalgh Jake Beaumont Louise Ansell
  2. 2. What is the difference between a vector based image and a bitmap (or raster) based image? <ul><li>A vector image uses geometrical formulas to represent images. The other way of representing graphical images is through bit-maps in which the image is made up of a pattern of dots (note that bit-maps are often referred to as raster graphics). Programs that allow you to create and manipulate vector graphics are called draw programs and programs that manipulate bit-map images are called paint programs. </li></ul><ul><li>Vector graphics are more flexible than bit-maps because they can be easily re-sized. In addition, images stored as vectors look better when displayed on high resolution printers and monitors. Bit-map images look the same, regardless of the resolution of the display. Another advantage of a vector graphic is that they often require less memory than bit-maps do. </li></ul><ul><li>Note that most output devices including dot matrix printers, laser printers and display monitors are raster devices (wide format printers being the exception). This means that all objects, even vector graphics, must be translated into bit-maps (or rasterised) before being output. </li></ul><ul><li>Vector graphics do not need to be translated in to bit-maps until the last possible minute, after all sizes and resolutions have been specified. </li></ul>
  3. 3. What is the difference between a GIF formatted file and a JPEG? Why are these different and to what different purposes are they suitable for? <ul><li>JPEG is a standardised image compression mechanism. JPEG is designed for compressing either full-colour (24 bit) or grey-scale digital images of &quot;natural&quot; (real-world) scenes. </li></ul><ul><li>The Graphics Interchange Format was developed in 1987 at the request of Compuserve, who needed a platform independent image format that was suitable for transfer across slow connections. It is a compressed (lossless) format (it uses the LZW compression) and compresses at a ratio of between 3:1 and 5:1 </li></ul><ul><li>JPEG is not going to displace GIF entirely. For some types of images, GIF is superior in image quality, file size, or both. One of the first things to learn about JPEG is which kinds of images to apply it to. </li></ul><ul><li>Generally speaking, JPEG is superior to GIF for storing full-color or grey-scale images of &quot;realistic&quot; scenes; that means scanned photographs and similar material. Any continuous variation in color, such as occurs in highlighted or shaded areas, will be represented more faithfully and in less space by JPEG than by GIF. </li></ul><ul><li>GIF does significantly better on images with only a few distinct colors, such as line drawings and simple cartoons. Not only is GIF lossless for such images, but it often compresses them more than JPEG can. For example, large areas of pixels that are all exactly the same color are compressed very efficiently indeed by GIF. JPEG can't squeeze such data as much as GIF does without introducing visible defects. (One implication of this is that large single-color borders are quite cheap in GIF files, while they are best avoided in JPEG files.) </li></ul><ul><li>Computer-drawn images (ray-traced scenes, for instance) usually fall between photographs and cartoons in terms of complexity. The more complex and subtly rendered the image, the more likely that JPEG will do well on it. The same goes for semi-realistic artwork (fantasy drawings and such). </li></ul><ul><li>JPEG has a hard time with very sharp edges: a row of pure-black pixels adjacent to a row of pure-white pixels, for example. Sharp edges tend to come out blurred unless you use a very high quality setting. Edges this sharp are rare in scanned photographs, but are fairly common in GIF files: borders, overlaid text, etc. The blurriness is particularly objectionable with text that's only a few pixels high. If you have a GIF with a lot of small-size overlaid text, don't JPEG it. </li></ul><ul><li>Plain black-and-white (two level) images should never be converted to JPEG; they violate all of the conditions given above. You need at least about 16 grey levels before JPEG is useful for grey-scale images. It should also be noted that GIF is lossless for grey-scale images of up to 256 levels, while JPEG is not. </li></ul>
  4. 4. What is the difference between and embedded graphic and a linked graphic in a Word or Powerpoint document? Which is the default and why is this important? How did you find out? <ul><li>Embedded graphics (the default image) are used when working on an imported file independently, whereas link graphic images remain independent of the illustrator file. • With embedded images the file size does not matter, whereas with linked images, the size can be altered. Embedded images are important as the file size does not matter and can be constantly moved between different files </li></ul>
  5. 5. What is a 'colour palette'? <ul><li>A colour palette is a set of colours defined for use within an image. Small palette files Eg. GIF files store a 4 or 8 bit index for each pixel. Image is a lot smaller than that of 24 bits. Large palette files Eg. TIF and JPG files store a 24 bit index for each of the millions of image pixels. </li></ul>
  6. 6. What is lossless compression? Do JPEG format files normally use this? Why is it important? <ul><li>Reducing file size without loss in image quality. JPEG files do not usually use this. This is important to reduce the artefacts in the image. </li></ul>
  7. 7. What does the FBS skills wiki say about using PNG files? Are there other new file formats to keep an eye on? <ul><li>Portable Network Graphics, a bitmapped image that employs lossless data compression Overcomes problems with GIF and JPEG files. It does not support animations </li></ul>
  8. 8. What is BAD about using .bmp format files in your work? Why should you try to avoid this? <ul><li>These files don’t support compression = very large files. The files are not supported by web browsers This should be avoided so that the files are not huge. </li></ul>
  9. 9. What is Flickr? Why might someone use this resource? Does it have an academic use or is it purely recreational? <ul><li>Flickr is a photo sharing website and web services suite. Allows photos to be tagged. Recreational: Photo sharing Academic: Bloggers as a photo repository. Allows categorizations of photos. </li></ul>

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