AWeb JFIF plugin

General

• Optional progressive display of loading images
• Support for scaling
• Support for CyberGraphics

Installation

1. Run the supplied Installer script. It will copy the necessary files to a drawer awebplugins in the drawer where the AWeb-II program is located.

   The installer script might ask you for a location to store temporary swap files during decoding of large images. You should select a drawer on your hard disk.
   
   

2. Run the .

Manual Installation

1. Copy the file named awebjfif.awebplugin to a location of your choice. The recommended location for plugins like this is a drawer awebplugins in the drawer where the AWeb-II program is located.
   
   
2. Select a drawer on your hard disk for the temporary swap files. These files may be needed during decoding of large images. Add the following assign to your S:User-Startup file if it isn't already there:

   assign JPEGTMP: swap_drawer

   where swap_drawer is the drawer you selected.
   
   
3. Start AWeb-II, open the browser settings and bring up the Viewers page. Select the entry for MIME type IMAGE/JFIF and change the following settings:
   • Action: "AWeb Plugin (A)"
   • Name: the location where you copied the file awebjfif.awebplugin
   • Arguments: leave blank or supply optional parameters, see below
   
   
   
4. Don't forget to save your settings.

Parameters

PROGRESS=0|number

Specifies the number of image scan lines to decode before the display is updated. A higher number is faster but results in chunkier building of the image. PROGRESS=1 gives the smoothest progressive display but is relatively slow. The default value is 4, which is a good compromise between speed and visual attractiveness.

If you specify PROGRESS=0, progressive display is disabled. The image is not displayed until decoding is ready.

DITHER=0|1|2

A number specifying the dither mode if colourmapped images are generated. This option takes only effect on screens with 256 colours or less. On CyberGraphics screens with more than 256 colours, true colour images are produced and no dithering is performed.

The number specifies the type of dithering as follows:

number	dither mode
0	No dithering (fast but low quality)
1	Ordered (compromise between no dithering and Floyd-Steinberg)
2	Floyd-Steinberg (best quality but slow). This is the default.

GRAYSCALE

Produce grayscale images. This is faster than colour images.

MAXMEM=number

Specifies the maximum amount of scratch memory (in kB) to be used for the decoding process of each image. Large images may take quite a lot of memory during decoding. If an image needs more memory than the specified maximum, a virtual memory system is used. After the image has been decoded, the scratch memory is released, even if the image is still displayed.

Default for this parameter is 1024 (= 1 megabyte). Note that the maximum is used on a per-image basis, not for all images together.

LOWPRI

The LOWPRI argument will run the decoder at a lower priority than default. If you are using your Amiga for other tasks while AWeb is downloading images, this feature helps you to keep the GUI responsive when many images are being decoded. However, if you are running CPU intensive tasks this argument could stop images from being processed alltogether.

Note that the LOWPRI argument might not be effective when you use a custom task scheduler like Executive. Use task name "AWebJFIF decoder" to configure the decoder task in custom schedulers.

Support

Disclaimer

Copyright

History

• Added LOWPRI argument.

• Removed possible decoder stalls.
• Much faster progressive display of scaled images.

• Didn't support progressive JPEGs (used old library version)
• Didn't support grayscale JPEGs.

• Initial version