Xara Webster - Creating GIF Files
GIFs and JPEGs
GIFs are best for graphics produced by an illustration package such as Webster unless you
use complex color graduations and shading. It is particularly suitable for simple graphics with
only a few colors. JPEGs are best for photographs and graphics with complex color
graduations. The JPEG format uses 16million colors (GIFs have a maximum of 256 colors)
and so graphics with a lot of colors look better in high color screen modes. However these are
only recommendations - you may need to try both formats to find which is best for your graphic.
GIF files can be interlaced. An interlaced GIF is shown on the screen at very low resolution as soon as it starts to download. A normal GIF is only shown on the page once the whole file has been downloaded.
Xara Webster provides three types of dithering. None means there is no dithering, Ordered uses an ordered (regular) dithering pattern and Error Diffusion uses a more complex dithering technique. In general, Error Diffusion gives the best results, but many images don't need dithering to give acceptable results. Using dithering increases file size (see the examples on this page).
GIFs can contain up to 256 colors but most images require far fewer colors. Reducing the number of colors makes the file size smaller and hence the GIF downloads quicker. Often you need to try a few experiments to find the minimum number of colors that's suitable for a particular image.
GIFs have three basic formats of 2 color, 16 color or 256 color. Confusingly you can create a 256 color GIF that only uses 16 colors. (Or a 16 color GIF that only uses 2 colors.) However this creates a larger file size than a true 16 color or 2 color GIF.
If you use GIF transparency, the transparency counts as one of the colors so a 16 color GIF with transparency can contain up to 15 colors.
You can choose between using the standard Netscape/Internet Explorer browser palette or an optimized palette. An optimized palette contains a range of colors best suited for the display of this image and gives excellent results. It is particularly useful when reducing the color depth to create small file sizes. Our advice is to generally use Optimized Palette.
Add system colors
Selecting this option adds 28 colors to the palette. These colors are the normal Windows system colors and a number of primary colors. This ensures the palette includes a spread of colors and may improve the quality of the image, particularly if you use dithering. You may need to experiment with this option to get the best results.
Without transparency, GIFs appear in the browser as a solid rectangle. Often by making parts of the GIF see-through, you produce eye catching graphics. To create see through areas, select those parts of the drawing you want to appear solid and then create the GIF with Transparency enabled. Areas not covered by selected objects are transparent in the GIF.
Note that if you create a transparent GIF file, one of the palette colors is used as the transparency. This means (for example) that a 2 color GIF contains one color and transparency.
Note that GIF transparency has a different meaning to Webster transparency. GIF transparency means that the background behind objects appears totally transparent. Webster transparency means that objects appear partly or completely transparent. Any area that has Webster transparency applied is always exported as though it was solid.
You can combine several individual GIFs into an animated GIF file. (Like the flashing
arrow next to the heading.) Creating animated GIFs is covered on another page.
Making GIFs download quickly over the Internet
GIFs compress the data in the file so the complexity of
the graphic matters more than the physical size. A simple graphic
with large areas of flat color compresses very well. Complex shading
and lots of colors compress less well. These are things to consider
as you create your graphic.
You can minimize the file size when you save the graphic by:
- Exporting the bitmap at 96 dpi, the resolution of the monitor
screen on a PC. Saving at a higher resolution increases the file size
without increasing quality.
- Using an optimized palette and reducing the number of colors.
You can type a number into the text field on the Export dialog
box. The minimum number of colors you need varies from image to
image. A simple graphic may need very few colors; a complex graphic
- Not including the system colors. These are a complete spectrum
of 28 basic colors which can often improve the appearance of dithering
(used to improve the appearance of shading).
- Not using dithering often gives acceptable results. Dithering
improves the appearance of shading but on-screen the difference
may not be noticeable.
Gray lines around the edge of the bitmap
An exported bitmap may show gray lines on one or more sides. This happens when the original drawing is not pixel aligned in Webster and the edge of the bitmap anti-aliases to the background.
To get rid of the gray line:
Snapping to the grid ensures your drawing is perfectly pixel aligned. By default, points on the grid are 10 pixels apart. You can change this spacing using Options on the Utilities menu.
- turn on Grid Snapping (on the Window menu
- move or resize the drawing so it snaps to the nearest points on the grid
- re-export the bitmap
Also see Creating Smooth Bitmap Edges.
Examples of GIFs with different options
These examples use Scroll 10. The GIFs are shown half their original size.
|4 colors with dithering. Size 1.96 KB
Not enough colors for this image as you can see from the white areas on the folds.
|8 colors with dithering. Size 2.51 KB
Better results but with some obvious color steps on the folds.
|16 colors with no dithering. Size 2.75 KB
Obvious banding on the folds. Worse than 8 colors with dithering.
|10 colors with dithering. Size 2.77 KB
Almost the same results as 16 colors with no dithering but produces a slightly larger file size.
|16 colors with dithering. Size 3.22 KB
Dithering doesn't give any improvement but produces a larger file size.
|32 colors with no dithering. Size 4.17 KB
Much better results. You can see that adding only another 16 colors gives a big improvement in appearance.
|64 colors with no dithering. Size 4.77 KB
Only you can decide which of 32, 64 or 128 colours gives acceptable results.
|128 colors with no dithering. Size 5.30 KB
The largest file size but relatively little improvement over 32 or 64 colors.
Checking the saved file in a browser
The easiest way to check the graphic is to drag-and-drop the saved
file onto a browser window. This loads the graphic and displays
it in the window. This method is simple to use and lets you quickly
choose between several different files.
The IMG HTML command
If the IMG command includes the width and height of the graphic,
the browser can load the text first and than load the graphics.
This doesn't load the page faster but it lets the viewer start
reading the text whilst the graphics download. It just seems quicker.
The IMG command should look like this
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page last updated 28 Apr 1997
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